U.S. patent application number 15/996236 was filed with the patent office on 2018-10-04 for microfluidic devices.
The applicant listed for this patent is Raindance Technologies, Inc.. Invention is credited to Darren Roy Link, David Marran, Jonathan M. Rothberg, Michael Weiner.
Application Number | 20180280897 15/996236 |
Document ID | / |
Family ID | 38529633 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180280897 |
Kind Code |
A1 |
Link; Darren Roy ; et
al. |
October 4, 2018 |
MICROFLUIDIC DEVICES
Abstract
The present invention provides novel microfluidic substrates and
methods that are useful for performing biological, chemical and
diagnostic assays. The substrates can include a plurality of
electrically addressable, channel bearing fluidic modules
integrally arranged such that a continuous channel is provided for
flow of immiscible fluids.
Inventors: |
Link; Darren Roy;
(Lexington, MA) ; Weiner; Michael; (Guilford,
CT) ; Marran; David; (Durham, CT) ; Rothberg;
Jonathan M.; (Guilford, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Raindance Technologies, Inc. |
Billerica |
MA |
US |
|
|
Family ID: |
38529633 |
Appl. No.: |
15/996236 |
Filed: |
June 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15886212 |
Feb 1, 2018 |
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15996236 |
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15480739 |
Apr 6, 2017 |
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15886212 |
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13779943 |
Feb 28, 2013 |
9981230 |
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15480739 |
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11803104 |
May 11, 2007 |
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13779943 |
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60920337 |
Mar 26, 2007 |
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60904293 |
Feb 28, 2007 |
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60903153 |
Feb 23, 2007 |
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60899258 |
Feb 2, 2007 |
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60876209 |
Dec 20, 2006 |
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60874640 |
Dec 12, 2006 |
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60874561 |
Dec 12, 2006 |
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60873766 |
Dec 8, 2006 |
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60860665 |
Nov 22, 2006 |
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60858279 |
Nov 8, 2006 |
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60858278 |
Nov 8, 2006 |
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60856540 |
Nov 3, 2006 |
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60856440 |
Nov 3, 2006 |
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60843374 |
Sep 8, 2006 |
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60843327 |
Sep 8, 2006 |
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60841716 |
Sep 1, 2006 |
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60837871 |
Aug 14, 2006 |
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60837695 |
Aug 14, 2006 |
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60834987 |
Jul 31, 2006 |
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60833151 |
Jul 24, 2006 |
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60819733 |
Jul 7, 2006 |
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60819734 |
Jul 7, 2006 |
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60815097 |
Jun 19, 2006 |
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60808614 |
May 25, 2006 |
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60799833 |
May 11, 2006 |
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60799834 |
May 11, 2006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01L 3/502784 20130101;
C12N 15/1068 20130101; C12Q 1/00 20130101; Y10T 137/87571 20150401;
C12Q 1/6806 20130101; C12Q 2565/628 20130101; G01N 21/05 20130101;
G01N 21/64 20130101; G01N 2035/00237 20130101; C12Q 1/6844
20130101; C12Q 1/6874 20130101; B01F 3/0807 20130101; B01L 3/502746
20130101; B01L 3/565 20130101; G01N 2201/024 20130101; B01L
3/502715 20130101; G01N 27/3275 20130101; G01N 35/08 20130101; B01L
2200/0673 20130101; B01L 2300/0861 20130101; B01L 2200/027
20130101; B01L 2200/10 20130101; B01L 2400/086 20130101; C12Q
1/6846 20130101; Y10T 137/87652 20150401; B01L 2400/0487 20130101;
C12Q 2565/629 20130101; C12Q 1/6855 20130101; C12Q 1/6869 20130101;
B01J 19/0093 20130101; Y10T 137/87619 20150401; B01L 2300/0864
20130101; B01F 13/0062 20130101; B01L 2200/0647 20130101; B01L
2300/0636 20130101; G01N 2021/0346 20130101; B01L 7/525 20130101;
B01L 2300/0867 20130101; B03C 5/005 20130101; G01N 2035/00326
20130101; B01L 2400/0415 20130101; B01L 2300/0816 20130101; B01L
2300/165 20130101; C12N 15/1086 20130101; B01L 2200/0636 20130101;
C12Q 1/6837 20130101; G01N 15/147 20130101; B01L 9/527 20130101;
B01L 2400/0424 20130101; B03C 5/026 20130101; C12Q 1/6806 20130101;
C12Q 2525/191 20130101; C12Q 2563/159 20130101; C12Q 2565/629
20130101; C12Q 1/6806 20130101; C12Q 2535/101 20130101; C12Q
2563/159 20130101; C12Q 2565/629 20130101; C12Q 1/6874 20130101;
C12Q 2563/149 20130101; C12Q 2563/159 20130101; C12Q 2565/629
20130101; C12Q 1/6844 20130101; C12Q 2563/159 20130101; C12Q
2565/629 20130101; C12Q 1/6806 20130101; C12Q 2531/113 20130101;
C12Q 2563/159 20130101; C12Q 2565/629 20130101; C12Q 1/6806
20130101; C12Q 2525/191 20130101; C12Q 2535/122 20130101; C12Q
2563/159 20130101; C12Q 2565/629 20130101; C12Q 1/6844 20130101;
C12Q 2525/191 20130101; C12Q 2535/122 20130101; C12Q 2563/159
20130101; C12Q 2565/629 20130101 |
International
Class: |
B01F 3/08 20060101
B01F003/08; C12Q 1/6869 20060101 C12Q001/6869; C12N 15/10 20060101
C12N015/10 |
Claims
1. A method for detecting a nucleic acid, the method comprising:
providing a nucleic acid and a microbead; encapsulating the nucleic
acid and the microbead into a droplet; conducting an amplification
reaction on the nucleic acid in the droplet in a manner that the
nucleic acid becomes bound to the microbead; and moving the
amplified bead-bound nucleic acid to a detection module comprising
an electrical sensor configured to detect an electrical
characteristic arising from the bead-bound nucleic acid.
2. The method of claim 1, wherein the electrical characteristic
comprises an electrical field emitted by the bead-bound nucleic
acid.
3. The method of claim 1, wherein the electrical characteristic
comprises capacitance or inductance.
4. The method of claim 1, wherein the electrical sensor is
connected to a processor.
5. The method of claim 4, wherein the processor causes the
bead-bound nucleic acids to be sorted.
6. The method of claim 1, wherein the electric sensor is embedded
within a wall of the detection module.
7. The method of claim 1, wherein the nucleic acid comprises DNA or
RNA.
8. The method of claim 1, wherein the nucleic acid comprises an
adaptor.
9. The method of claim 1, wherein the droplets comprise
primers.
10. The method of claim 9, wherein the primers are coupled to the
microbeads.
11. The method of claim 1, further comprising shearing the nucleic
acid
12. The method of claim 1, wherein the droplets are surrounded by
an immiscible carrier fluid.
13. The method of claim 1, wherein the amplification reaction
comprises a polymerase chain reaction.
14. The method of claim 1, wherein the amplification reaction
comprises flowing the droplets through a microfluidic device to
expose the droplets to thermocycling.
15. The method of claim 5, wherein sorting comprises distinguishing
droplets comprising amplified bead-bound nucleic acid fragments
from droplets that do not comprise amplified bead-bound nucleic
acid fragments.
Description
RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S.
Nonprovisional application Ser. No. 15/886,212, filed Feb. 1, 2018,
which is a continuation of U.S. Nonprovisional application Ser. No.
15/480,739, filed Apr. 6, 2017, which is a continuation of U.S.
Nonprovisional application Ser. No. 13/779,943, filed Feb. 28, 2013
(now U.S. Pat. No. 9,981,230), which is a continuation application
of U.S. Nonprovisional application Ser. No. 11/803,104, filed May
11, 2007, which claims priority to, and the benefit of, U.S.
Provisional Application Nos. 60/799,833 filed on May 11, 2006;
60/799,834 filed on May 11, 2006; 60/808,614 filed on May 25, 2006;
60/815,097 filed on Jun. 19, 2006; 60/819,733 filed on Jul. 7,
2006; 60/819,734 filed on Jul. 7, 2006; 60/841,716 filed on Sep. 1,
2006; 60/843,374 filed on Sep. 8, 2006; 60/833,151 filed on Jul.
24, 2006; 60/834,987 filed on Jul. 31, 2006; 60/837,871 filed on
Aug. 14, 2006; 60/837,695 filed on Aug. 14, 2006; 60/843,327 filed
on Sep. 8, 2006; 60/856,540 filed on Nov. 3, 2006; 60/856,440 filed
on Nov. 3, 2006; 60/874,561 filed on Dec. 12, 2006; 60/858,279
filed on Nov. 8, 2006; 60/858,278 filed on Nov. 8, 2006; 60/874,640
filed on Dec. 12, 2006; 60/860,665 filed on Nov. 22, 2006;
60/873,766 filed on Dec. 8, 2006; 60/876,209 filed on Dec. 20,
2006; 60/899,258 filed on Feb. 2, 2007; 60/903,153 filed on Feb.
23, 2007; 60/904,293 filed on Feb. 28, 2007; 60/920,337 filed on
Mar. 26, 2007. The contents of each of these applications are
incorporated herein by reference in their entirety.
FIELD OF INVENTION
[0002] The present invention generally relates to systems and
methods for the formation and/or control of fluidic species, and
articles produced by such systems and methods. More particularly,
the present invention relates to the development of high throughput
microfluidic devices for precision fluid handling and use of such
systems in various biological, chemical, or diagnostic assays.
BACKGROUND
[0003] The manipulation of fluids to form fluid streams of desired
configuration, discontinuous fluid streams, droplets, particles,
dispersions, etc., for purposes of fluid delivery, product
manufacture, analysis, and the like, is a relatively well-studied
art. For example, highly monodisperse gas bubbles, less than 100
microns in diameter, have been produced using a technique referred
to as capillary flow focusing. In this technique, gas is forced out
of a capillary tube into a bath of liquid, where the tube is
positioned above a small orifice, and the contraction flow of the
external liquid through this orifice focuses the gas into a thin
jet which subsequently breaks into equal-sized bubbles via a
capillary instability. A similar arrangement can be used to produce
liquid droplets in air.
[0004] Microfluidic systems have been described in a variety of
contexts, typically in the context of miniaturized laboratory
(e.g., clinical) analysis. Other uses have been described as well.
For example, International Patent Application Publication No. WO
01/89788 describes multi-level microfluidic systems that can be
used to provide patterns of materials, such as biological materials
and cells, on surfaces. Other publications describe microfluidic
systems including valves, switches, and other components.
[0005] Precision manipulation of streams of fluids with
microfluidic devices is revolutionizing many fluid-based
technologies. Networks of small channels are a flexible platform
for the precision manipulation of small amounts of fluids. The
utility of such microfluidic devices depends critically on enabling
technologies such as the microfluidic peristaltic pump,
electrokinetic pumping, dielectrophoretic pump or electrowetting
driven flow. The assembly of such modules into complete systems
provides a convenient and robust way to construct microfluidic
devices. However, virtually all microfluidic devices are based on
flows of streams of fluids; this sets a limit on the smallest
volume of reagent that can effectively be used because of the
contaminating effects of diffusion and surface adsorption. As the
dimensions of small volumes shrink, diffusion becomes the dominant
mechanism for mixing leading to dispersion of reactants; moreover,
surface adsorption of reactants, while small, can be highly
detrimental when the concentrations are low and volumes are small.
As a result current microfluidic technologies cannot be reliably
used for applications involving minute quantities of reagent; for
example, bioassays on single cells or library searches involving
single beads are not easily performed. An alternate approach that
overcomes these limitations is the use of aqueous droplets in an
immiscible carrier fluid; these provide a well defined,
encapsulated microenvironment that eliminates cross contamination
or changes in concentration due to diffusion or surface
interactions. Droplets provide the ideal microcapsule that can
isolate reactive materials, cells, or small particles for further
manipulation and study. However, essentially all enabling
technology for microfluidic systems developed thus far has focused
on single phase fluid flow and there are few equivalent active
means to manipulate droplets requiring the development of droplet
handling technology. While significant advances have been made in
dynamics at the macro- or microfluidic scale, improved techniques
and the results of these techniques are still needed. For example,
as the scale of these reactors shrinks, contamination effects due
to surface adsorption and diffusion limit the smallest quantities
that can be used. Confinement of reagents in droplets in an
immiscible carrier fluid overcomes these limitations, but demands
new fluid-handling technology.
[0006] Furthermore, the underlying physics of the influence of
electric fields on fluids is well known. The attractive and
repulsive forces produced by an electric field on positive or
negative charges give rise to the forces on charged fluid elements,
the polarization of non-polar molecules, and the torque on polar
molecules which aligns them with the field. In a non-uniform field,
because the force on the positively charged portion of the
distribution is different than the force on the negatively charged
portion, polar molecules will also experience a net force toward
the region of higher field intensity. In the continuum limit, the
result is a pondermotive force in the fluid. In the limit of high
droplet surface tension, it is useful to describe the net
pondermotive force on a droplet as if it were a rigid sphere:
F=qE+2.pi.(.epsilon..sub.m)r.sup.3(K).DELTA.E.sup.2.
where the first term is the electrophoretic force on the droplet (q
is the net droplet charge and E is the electric field), and the
second term is the dielectrophoretic force (r is the radius of the
sphere, R(K) is the real part of the Clausius-Mossotti factor
K=(.epsilon.*.sub.p-.epsilon.*.sub.m)/(.epsilon.*.sub.p+2.epsilon.*.sub.-
m),
and .epsilon.*.sub.p and .epsilon.*.sub.m are the complex
permittivities of the droplet and carrier fluid).
[0007] Although utility of electrophoretic control of droplets is
great, it does have significant limitations. First, the charging of
droplets is only effectively accomplished at the nozzle. Second,
the discharge path required to eliminate screening effects also
discharges the droplets. Third, finite conductivity of the carrier
fluid, however small, will eventually discharge the droplets.
Therefore, once the droplet is formed, there is essentially only
one opportunity to perform any pondermotive function which relies
on the droplet's charge density (such as coalescing oppositely
charged droplets through their mutual Coulombic attraction, or
electrophoretically sorting a droplet), and that function can only
be performed as long as sufficient charge has not leaked off of the
droplet.
[0008] Thus, it would be desirable to develop an electrically
addressable emulsification system that combines
compartmentalization and electrical manipulation, which allows for
multi-step chemical processing, including analysis and sorting, to
be initiated in confinement with exquisite timing and metering
precision, for use in a variety of chemical, biological, and
screening assays, in which the cost and time to perform such assays
would be drastically reduced. It would also be desirable to develop
a device using dielectrophoretic force (which does not rely on
charge density) to manipulate droplets so that more than one
electrical pondermotive function can be carried out following a
significantly long delay from droplet formation.
SUMMARY OF THE INVENTION
[0009] The present invention provides substrates having individual
fluid handling modules that can be combined into fluid processing
systems so as to perform multi-step processing of isolated
components, which is essential to perform biological, chemical and
diagnostic applications, quickly, effectively and inexpensively.
Using principles based on the electrical manipulation of droplets,
the microfluidic substrates of the present invention can
encapsulate reagents into droplets, which can be combined,
analyzed, and sorted.
[0010] The present invention provides a microfluidic substrate. The
substrate can include a plurality of Microfluidic modules
integrally arranged with each other so as to be in fluid
communication. The substrate can include, for example, (i) at least
one inlet module having at least one inlet channel adapted to carry
at least one dispersed phase fluid, (ii) at least one main channel
adapted to carry at least one continuous phase fluid, wherein the
inlet channel is in fluid communication with the main channel at a
junction, wherein the junction includes a fluidic nozzle designed
for flow focusing such that the dispersed phase fluid is immiscible
with the continuous phase fluid and forms a plurality of highly
uniform, monodisperse droplets in the continuous phase fluid. The
flow of the dispersed phase and continuous phase can be pressure
driven, for example. The dispersed phase (e.g. droplets) can be
neutral or have no charge and these droplets can be manipulated
(e.g., coalesced, sorted) within a electric field in the continuous
phase fluid.
[0011] The inlet module can further include at least one
self-aligning fluidic interconnect apparatus to connect the inlet
channel to a means for introducing a sample fluid to the channel,
wherein the apparatus forms a radial seal between the microfluidic
substrate and the means for introducing sample. The means can
include, for example, a well or reservoir, which can be temperature
controlled. The well or reservoir can optionally include an
acoustic actuator.
[0012] The microfluidic substrate can include one or more
additional modules, including but not limited to, coalescence
module, detection module, sorting module, collection module, waste
module, delay module (e.g., heating and cooling modules), droplet
spacing module, mixing module, UV-release module, division module
and/or reordering module. These modules are in fluid communication
with the main channel. There may be zero, one, or more of each of
the modules.
[0013] The substrate can further include at least one coalescence
module downstream from and in fluid communication with the inlet
module via the main channel including a coalescence apparatus,
wherein two or more droplets passing there through are coalesced to
form a nanoreactor.
[0014] The substrate can further include at least one detection
module downstream from and in fluid communication with the
coalescence module. The detection module can include, for example,
a detection apparatus for evaluating the contents and/or
characteristics of the nanoreactor. The detection apparatus can
include an optical or electrical detector.
[0015] The substrate can further include a sorting module
downstream from and in fluid communication with the detection
module. The sorting module can include, for example, a sorting
apparatus adapted to direct the nanoreactor into or away from a
collection module in response to the contents or characterization
of the nanoreactor evaluated in the detection module. The channels
in the sorting module can include an asymmetric bifurcation
geometry or an asymmetric bifurcation flow.
[0016] The coalescence apparatus and the sorting apparatus can
include one or more electrodes, or a patterned electrically
conductive layer, which are capable of generating an electric
field. The electrodes can be made from electrically conductive
materials, and can be integrally contained in one or more channels
isolated from the main and inlet channels of the substrate. The
electrically conductive materials can be metal alloy components or
organic materials. The electrically conductive material can be an
epoxy resin including one or more electrically conductive
particles. The electrically conductive particles can be silver
particles.
[0017] The coalescence module can further include an expanded
portion of the main channel between the electrodes to bring
successive droplets into proximity, whereby the paired droplets are
coalesced within the electric field. The coalescence module can
further include a narrowed portion of the main channel to center
droplets within the main channel prior to the expanded portion of
the main channel between the electrodes.
[0018] The channels of the microfluidic substrate can be coated
with an anti-wetting or blocking agent for the dispersed phase. The
anti-wetting or blocking agent can include, for example, a silica
primer layer followed by a perfluoroalkylalkylsilane compound, an
amorphous soluble perfloropolymer, BSA, PEG-silane or fluorosilane.
The channels of the microfluidic substrate can include well-like
indentations to slow, stop or react contents of droplets.
[0019] The substrate can further include a collection module
connected to a means for storing a sample from the substrate and a
waste module connected to a means for collecting a sample discarded
from the substrate. The means can be a well or reservoir, which can
be temperature controlled.
[0020] The substrate can further include a delay module in fluid
communication with the main channel downstream of the coalescence
module and upstream of the detection module. The delay module can
be a delay line, serpentine channel, a buoyant hourglass, or an
off-chip volume. Preferably, a serpentine channel is used to time
delays less than 1 hour. Preferably, an off-chip volume is used to
time delays longer than 1 hour. The delay module can further
include heating and cooling regions.
[0021] The substrate can further include a mixing module in fluid
communication with the main channel downstream of the coalescence
module and upstream of the detection module.
[0022] The substrate can further include a UV-release module in
fluid communication with the main channel downstream of the inlet
module and upstream of the coalescence module.
[0023] The substrate can further include a droplet spacing module
in fluid communication with the main channel downstream of the
inlet module to allow appropriate droplets to come with proximity
for coalescence.
[0024] The continuous phase used in the channels of the
microfluidic substrate can be a non-polar solvent such as, for
example, a fluorocarbon oil. The continuous phase can further
include one or more additives such as a surfactant or
fluorosurfactant in order to stabilize the droplets. The
fluorosurfactant can be a perfluorinated polyether, for
example.
[0025] The dispersed phase of the microfluidic substrate can
include a library of droplets of the same or different sizes (i.e.,
an emulsion stream) or a continuous aqueous stream. The library of
droplets can include, for example, a biological or chemical
material such as tissues, cells, particles, proteins, antibodies,
amino acids, nucleotides, small molecules, and pharmaceuticals. The
biological/chemical material can include a label such as a DNA tag,
dye, a quantum dot or a radio frequency identification tag. The
library of library of droplets can include a label such as a change
in viscosity, a change in opacity, a change in volume, a change in
density, a change in pH, a change in temperature, a change in
dielectric constant, a change in conductivity, a change in the
amount of beads present in the droplets, a change in the amount of
flocculent in the droplets, a change in the amount of a selected
solvent within the droplets or the change in the amount of any
measurable entity within the droplets, or combinations thereof. A
label can be detected by fluorescence polarization, fluorescence
intensity, fluorescence lifetime, fluorescence energy transfer, pH,
ionic content, temperature or combinations thereof.
[0026] The present invention also provides a microfluidic substrate
including, for example, (i) at least one inlet module having at
least one inlet channel adapted to carry at least one dispersed
phase fluid; (ii) at least one main channel adapted to carry at
least one continuous phase fluid, wherein the inlet channel is in
fluid communication with the main channel at a junction, wherein
the junction includes a fluidic nozzle designed for flow focusing
such that the dispersed phase fluid is immiscible with the
continuous phase fluid and forms a plurality of highly uniform,
monodisperse droplets in the continuous phase fluid; (iii) at least
one nanoreactor division module downstream from the inlet module
wherein the main channel is divided into at least two division
channels and the nanoreactor is split into at least two daughter
nanoreactors; (iv) at least one second inlet channel adapted to
carry at least one second dispersed phase fluid wherein the inlet
channel is in fluid communication with at least one of the
divisional channels at a junction, wherein the junction includes a
fluidic nozzle designed for flow focusing such that the second
dispersed phase fluid is immiscible with the continuous phase fluid
and forms a plurality of highly uniform, monodisperse droplets in
the continuous phase fluid; (v) at least one coalescence module
downstream from and in fluid communication with the inlet module
via the main channel including a coalescence apparatus, wherein at
least one droplet from step (ii) and at least one droplet from step
(iv) passing there through are coalesced; (vi) at least one reorder
module downstream from the dividing module such that the daughter
nanoreactors from the division channel are reordered in proximity
but not coalesced; and (vii) at least one detection module
downstream from the reorder module, the detection module including
a detection apparatus for evaluating the contents or
characteristics of at least one of nanoreactors or droplets in
proximity.
[0027] The microfluidic substrate can also include a sorting module
in proximity to and in fluid communication with the detection
module, the sorting module including a sorting apparatus adapted to
direct the droplet or nanoreactor into or away from a collection
module in response to the contents or characterization of the
droplet or nanoreactor evaluated in the detection module.
[0028] The detection module can evaluate the contents of two
nanoreactors or droplets in proximity and the sorting module can
direct the droplets or nanoreactors into or away from a collection
module in response to the ratio of the contents or characterization
of the droplets or nanoreactors evaluated in the detection
module.
[0029] The present invention also provides a method of producing
microfluidic substrate including, for example, (i) providing a base
plate, wherein the base plate comprises a flat surface; (ii)
providing a master including the pattern of the channels and
electrodes of a microfluidic substrate; (iii) providing a molding
cavity, wherein the molding cavity comprises an opening for molding
an elastomeric substrate; (iv) assembling the base plate, master
and molding cavity, such that the master is placed between the base
plate and molding cavity and wherein the master pattern is located
directly under and aligned to the opening for molding an
elastomeric substrate; (v) providing a top plate containing one or
more sliding molding pins used to form one or more fluid and/or
electrical interconnects; (vi) assembling the top plate onto the
molding cavity of step d, such that the sliding molding pins
contact points on the pattern of channels and electrodes on the
master; (vi) introducing a liquid elastomeric polymer into the
opening on the molding cavity such that it contacts the master;
(vii) solidifying the elastomeric polymer within the molding
cavity; (viii) removing the solidified elastomeric polymer
substrate from the top plate, bottom plate and molding cavity
assembly; and (ix) bonding the solidified elastomeric polymer
substrate to compatible polymeric or non-polymeric media. The
sliding molding pins can be surrounded by an elastomeric sleeve.
The present invention also provides a microfluidic device produces
by the methods provided.
[0030] The master is generated by photolithography,
photolithography and converted to a durable metal master,
micromachining or by rapid prototyping methods such as
stereolithography. The master can be a silicon or glass substrate
patterned with photoresist. Preferably, the master is a silicon or
glass substrate patterned with SU-8.
[0031] The elastomeric polymer can be a silicone elastomeric
polymer. Preferably, the silicone elastreric polymer is
polydimethylsiloxane. The elastomeric polymer can be solidified by
curing. The elastomeric polymer can be treated with high intensity
oxygen or air plasma to permit bonding to the compatible polymeric
or non-polymeric media. The polymeric and non-polymeric media can
be glass, silicon, silicon oxide, quartz, silicon nitride,
polyethylene, polystyrene, glassy carbon, or epoxy polymers.
[0032] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. All
publications, patent applications, patents, and other references
mentioned herein are incorporated by reference in their entirety.
In the case of conflict, the present specification, including
definitions, will control. In addition, the materials, methods, and
examples are illustrative only and not intended to be limiting.
[0033] Other features and advantages of the invention will be
apparent from the following detailed description and claims.
BRIEF DESCRIPTION OF DRAWINGS
[0034] Non-limiting embodiments of the present invention will be
described by way of example with reference to the accompanying
drawings, which are schematic and are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component illustrated is typically represented by a single numeral.
For the purposes of clarity, not every component is labeled in
every drawing, nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. In the
drawings:
[0035] FIG. 1 is an schematic illustrating the interacting modules
of a microfluidic device of the present invention.
[0036] FIGS. 2A-B show dual and single oil versions of the nozzle
concept using a small ferrule for the nozzle section. FIGS. 2C-D
show the same nozzles made directly out of small bore tubing (the
"nozzle" runs the entire length of the tubing).
[0037] FIG. 3 shows the expansion of the nozzle ferrule concept
shown in FIGS. 2A and 2B.
[0038] FIG. 4 shows the expansion of the nozzle section contained
in the ferrule.
[0039] FIG. 5A shows the operation of the nozzle in Aspiration Mode
and 5B shows the operation of the nozzle in Injection Mode.
[0040] FIGS. 6A-D show a reservoir based sample emulsification.
FIG. 6A shows where the well is initially filled with a fluid with
lower density than the sample to be introduced. 6B-6D show a more
dense sample droplet being introduced to the well and settling to
the bottom of the well and being transported to the nozzle. 6E
shows that the oil lines would begin flowing at their prescribed
rates, while the collection or waste port would begin withdrawing
at a rate.
[0041] FIGS. 7A-E illustrate a sample introduction when the sample
is less dense than the fluid in the sample port, which is an
alternative scheme used to introduce samples that are less dense
than the oil used to emulsify the sample. 7A shows that the sample
port could be filled with the emulsification oil through backflow
from the nozzle prior to introduction of the sample. 7B-7D show a
sample tip connected to a pump capable of driving the sample into
the device. The pump is started up as the tip is inserted into the
device, injecting sample in to the port. 7E shows that the oil
lines would begin flowing at their prescribed rates, while the
collection or waste port would begin withdrawing at a rate.
[0042] FIG. 8 illustrates a nozzle that formed directly into the
fitting used to connect the collection syringe to a syringe tip
(e.g. capillary tubing) in order to create a monodisperse emulsion
directly from a library well. Step 1 shows the aspiration of the
sample can be accomplished by running the collection syringe in
withdrawal mode at a flow rate (Q3) above the flow rate of the two
oil syringes. Step 2 shows the appropriate volume of sample loaded
into the capillary tubing, and the capillary tubing would be
removed from the sample well, an air bubble, and possibly a
cleaning solution would be aspirated. Step 3 shows when almost all
of the sample has been emulsified, the collection syringe
withdrawal rate would either be reduced below the oil flow rates,
stopped, or set to infuse at some nominal rate.
[0043] FIGS. 9A-C illustrate a two phase system where the reagent
is injected on top of the 2nd, immiscible phase. (FIG. 9A) During
injection, prior to transition from 1st phase to 2nd phase. (FIG.
9B) 2nd phase just entering the transfer lines. (FIG. 9C) 2nd phase
has completely filled the transfer line and pushed the entire
volume of reagent through the system.
[0044] FIG. 10 illustrates sandwiching an ultra-small volume of
fluid (i.e., sub-nanoliter) between two solutions having different
densities.
[0045] FIG. 11 illustrates possible interconnect designs for use
with PDMS devices.
[0046] FIG. 12 illustrates self-alignment of fluidic interconnect
FIG. 13 illustrates the interconnects needed for each tube molded
into a single monolithic self-aligned part.
[0047] FIG. 14 shows a schematic of a molding tool based on this
concept. The pins (orange) are captured within an elestomeric
molded sleeve and a compression plate made from a rigid backer
plate and foam rubber is used to apply gentle even pressure to the
pins and generate the force needed to make the pins uniformly
contact the master.
[0048] FIG. 15 is a schematic diagram of an improved coalescence
module that shows an optional small constriction (neckdown) just
before this expansion can be used to better align the droplets on
their way into the coalescence point.
[0049] FIG. 16 illustrates that fluorescence polarization (FP)
measures the tumbling rate of a compound in solution and is a
function of it's volume (in most cases, volume is correlated with
MW)
[0050] FIG. 17 shows the fluorescence polarization of three
different compounds. Results of reading polarization in 18,000
drops containing 3 distinct species (FC, BTFC, and BTFC bound to
SA). Ideal for reading results of drug screening assays, protein
interactions, or DNA hybridization.
[0051] FIG. 18A illustrates encoding a liquid solution using both
overall fluorescence polarization and overall dye intensity within
droplets; FIG. 18B shows that multiple colors of fluorescence
polarization and FI increases the number of possible labels. Ten
intensity levels with ten fluorescence polarization levels on two
colors yields 10,000 labels.
[0052] FIG. 19 illustrates FPcoding using dyes having different
fluorescence lifetimes. These were made one element at a time,
stored in a single syringe overnight and then loaded back on chip.
The codes were made by using a ratio of two different dyes, one
with a short lifetime and hence high FP and one with a long
lifetime and correspondingly low FP. The mixtures have intermediate
FP signals. The intensity is tuned by controlling the overall
concentration of the two dyes.
[0053] FIG. 20A-20D illustrate the sorting and/or splitting of
droplets in accordance with another embodiment of the invention
FIG. 21A-F shows the possible flow geometries used in an asymmetric
sorting application.
[0054] FIGS. 22A-E show the possible electrode geometries used in
an asymmetric sorting application. FIG. 22A shows the design using
sharp tipped electrodes. FIG. 22B shows broad tipped electrodes to
increase the interaction time between the droplets and the electric
field (the tips could be many drop diameters long). FIG. 22C shows
electrodes straddling the collection line. FIG. 22D shows
electrodes on opposite sides of the main channel. FIG. 22E shows an
Asymmetric Electrode Pair (the asymmetry may be present on any of
the other electrode pair layouts as well).
[0055] FIG. 23 shows a schematic of a device that split droplets,
performs different experiments on the two daughter droplets and
then reorders so that they pass sequential through the detector
[0056] FIG. 24A, shows geometric parameters defining the obstacle
matrix. FIG. 24B shows three fluid streams. FIG. 24C shows a
particle with a radius that is larger than lane 1 follows a
streamline passing through the particle's center (black dot).
[0057] FIG. 25 shows high-resolution separation of fluorescent
microspheres with diameters of 0.80 um (green), 0.90 um (red), and
1.03 um (yellow), with a matrix of varying gap size.
[0058] FIG. 26 is a schematic illustrating the separation by
deterministic lateral displacement in an array of microposts, with
an example row shift fraction of one-third.
[0059] FIG. 27 shows a dideoxynucleotide sequencing on a
microfabricated chip. Shown is one embodiment for a DNA sequencing
chip design. Template DNA and primers are combined at step `add 1`
and the reaction is incubated at 95.degree. C. for a hot start
(position 1). The reaction then cycles 20-30 times (position 2)
before the addition of SAP and Exol at `add 2.` The reaction is
incubated at 37.degree. C. for a pre-defined time-period and then
the SAP and Exol enzymes are inactivated at 95.degree. C. (position
`4`). The SAP/Exol procedure degrades nucleotides and
single-stranded DNA (primers) remaining after PCR. The universal
sequencing primers, ddNTPs and buffers are added at `add 3,` and
the PCR sequencing reaction is allowed to proceed at position `5.`
The final reaction product is collected and can be stored
off-chip.
[0060] FIG. 28A, shows a schematic of the TempliPhi amplification
process using rolling circle amplification. FIG. 28B illustrates a
transcription mediated reaction. FIG. 28C illustrates
strand-displacement amplification. FIG. 28D shows a schematic
diagram of helicase-dependent amplification.
[0061] FIGS. 29A-D illustrate emulsion-based sample preparation,
sample preparation and DNA sequencing. Random libraries of DNA
fragments are generated by shearing an entire genome and isolating
single DNA molecules by limiting dilution. In FIG. 29A, genomic DNA
is isolated, fragmented, ligated to adapters and separated into
single strands. FIG. 29B shows microscope photograph of emulsion
showing droplets containing a bead and empty droplets. FIG. 29C
shows a scanning electron micrograph of a portion of a fiber-optic
slide, showing fiber-optic cladding and wells before bead
deposition. FIG. 29D shows the sequencing instrument and its
sub-systems.
[0062] FIG. 30 shows one method for isolating antibodies on a
microfluidic device.
[0063] FIG. 31 shows an alternate method for isolating antibodies
on a microfluidic device.
[0064] FIG. 32 shows the method of the present invention for
isolating antibodies on the microfluidic device. The right panel is
a diagram of individual steps proposed to amplify signal of
interacting antibody and antigen. The left panel is a schematic as
would be designed for a chip to be used on microfluidic device.
[0065] FIG. 33 shows the genetic selection for full length antibody
clones. A genetic selection can be used to enrich for full-length
antibody clones by transforming E. coli and selecting for clones
able to grow on medium in which a suitable sugar is the only carbon
source.
[0066] FIG. 34 is a schematic representation of a multi-step chip
according to the invention. 1.sup.st stage: droplets are sent into
C2, the collection port; 2.sup.nd stage: 1.sup.st stage emulsion
collected into C2 is reinjected back into the chip and merged with
the droplets formed in the second stage nozzle.
[0067] FIG. 35 shows karyotyping using spectral probes that allow
all 23 pairs of human chromosomes to be seen at one time, with each
pair of chromosomes painted in a difference fluorescent color.
[0068] FIG. 36 shows the future BioBased Economy with six building
blocks based on renewable 30 biomass.
[0069] FIG. 37 shows the 8 non-renewable building blocks based on
petroleum.
DETAILED DESCRIPTION
[0070] The microfluidic devices and methods of use described herein
are based on the creation and electrical manipulation of aqueous
phase droplets completely encapsulated by an inert immiscible oil
stream. This combination enables precise droplet generation, highly
efficient, electrically addressable, droplet coalescence, and
controllable, electrically addressable single droplet sorting. The
microfluidic devices include one or more channels and modules. A
schematic illustrating one example of interacting modules of a
microfluidic substrate is shown in FIG. 1. The integration of these
modules is an essential enabling technology for a droplet based,
high-throughput microfluidic reactor system.
[0071] The microfluidic devices of the present invention can be
utilized for numerous biological, chemical, or diagnostic
applications, as described in further detail herein.
Substrates
[0072] The microfluidic device of the present invention includes
one or more analysis units. An "analysis unit" is a microsubstrate,
e.g., a microchip. The terms microsubstrate, substrate, microchip,
and chip are used interchangeably herein. The analysis unit
includes at least one inlet channel, at least one main channel, at
least one inlet module, at least one coalescence module, and at
least one detection module. The analysis unit can further includes
one or more sorting modules. The sorting module can be in fluid
communication with branch channels which are in fluid communication
with one or more outlet modules (collection module or waste
module). For sorting applications, at least one detection module
cooperates with at least one sorting module to divert flow via a
detector-originated signal. It shall be appreciated that the
"modules" and "channels" are in fluid communication with each other
and therefore may overlap; i.e., there may be no clear boundary
where a module or channel begins or ends. A plurality of analysis
units of the invention may be combined in one device. The analysis
unit and specific modules are described in further detail
herein.
[0073] The dimensions of the substrate are those of typical
microchips, ranging between about 0.5 cm to about 15 cm per side
and about 1 micron to about 1 cm in thickness. A substrate can be
transparent and can be covered with a material having transparent
properties, such as a glass coverslip, to permit detection of a
reporter, for example, by an optical device such as an optical 25
microscope. The material can be perforated for functional
interconnects, such as fluidic, electrical, and/or optical
interconnects, and sealed to the back interface of the device so
that the junction of the interconnects to the device is leak-proof.
Such a device can allow for application of high pressure to fluid
channels without leaking.
[0074] A variety of materials and methods, according to certain
aspects of the invention, can be used to form any of the described
components of the systems and devices of the invention. In some
cases, the various materials selected lend themselves to various
methods. For example, various components of the invention can be
formed from solid materials, in which the channels can be formed
via molding, micromachining, film deposition processes such as spin
coating and chemical vapor deposition, laser fabrication,
photolithographic techniques, etching methods including wet
chemical or plasma processes, and the like. See, for example,
Scientific American, 248:44-55, 1983 (Angell, et al). At least a
portion of the fluidic system can be formed of silicone by molding
a silicone chip. Technologies for precise and efficient formation
of various fluidic systems and devices of the invention from
silicone are known. Various components of the systems and devices
of the invention can also be formed of a polymer, for example, an
elastomeric polymer such as polydimethylsiloxane ("PDMS"),
polytetrafluoroethylene ("PTFE") or Teflon.RTM., or the like.
[0075] The channels of the invention can be formed, for example by
etching a silicon chip using conventional photolithography
techniques, or using a micromachining technology called "soft
lithography" as described by Whitesides and Xia, Angewandte Chemie
International Edition 37, 550 (1998). These and other methods may
be used to provide inexpensive miniaturized devices, and in the
case of soft lithography, can provide robust devices having
beneficial properties such as improved flexibility, stability, and
mechanical strength. When optical detection is employed, the
invention also provides minimal light scatter from molecule, cell,
small molecule or particle suspension and chamber material.
[0076] Different components can be formed of different materials.
For example, a base portion including a bottom wall and side walls
can be formed from an opaque material such as silicone or PDMS, and
a top portion can be formed from a transparent or at least
partially transparent material, such as glass or a transparent
polymer, for observation and/or control of the fluidic process.
Components can be coated so as to expose a desired chemical
functionality to fluids that contact interior channel walls, where
the base supporting material does not have a precise, desired
functionality. For example, components can be formed as
illustrated, with interior channel walls coated with another
material. Material used to form various components of the systems
and devices of the invention, e.g., materials used to coat interior
walls of fluid channels, may desirably be selected from among those
materials that will not adversely affect or be affected by fluid
flowing through the fluidic system, e.g., material(s) that is
chemically inert in the presence of fluids to be used within the
device.
[0077] Various components of the invention when formed from
polymeric and/or flexible and/or elastomeric materials, and can be
conveniently formed of a hardenable fluid, facilitating formation
via molding (e.g. replica molding, injection molding, cast molding,
etc.). The hardenable fluid can be essentially any fluid that can
be induced to solidify, or that spontaneously solidifies, into a
solid capable of containing and/or transporting fluids contemplated
for use in and with the fluidic network. In one embodiment, the
hardenable fluid comprises a polymeric liquid or a liquid polymeric
precursor (i.e. a "prepolymer"). Suitable polymeric liquids can
include, for example, thermoplastic polymers, thermoset polymers,
or mixture of such polymers heated above their melting point. As
another example, a suitable polymeric liquid may include a solution
of one or more polymers in a suitable solvent, which solution forms
a solid polymeric material upon removal of the solvent, for
example, by evaporation. Such polymeric materials, which can be
solidified from, for example, a melt state or by solvent
evaporation, are well known to those of ordinary skill in the art.
A variety of polymeric materials, many of which are elastomeric,
are suitable, and are also suitable for forming molds or mold
masters, for embodiments where one or both of the mold masters is
composed of an elastomeric material. A non-limiting list of
examples of such polymers includes polymers of the general classes
of silicone polymers, epoxy polymers, and acrylate polymers. Epoxy
polymers are characterized by the presence of a three-membered
cyclic ether group commonly referred to as an epoxy group,
1,2-epoxide, or oxirane. For example, diglycidyl ethers of
bisphenol A can be used, in addition to compounds based on aromatic
amine, triazine, and cycloaliphatic backbones. Another example
includes the well-known Novolac polymers. Non-limiting examples of
silicone elastomers suitable for use according to the invention
include those formed from precursors including the chlorosilanes
such as methylchlorosilanes, ethylchlorosilanes,
phenylchlorosilanes, etc.
[0078] Silicone polymers are preferred, for example, the silicone
elastomer polydimethylsiloxane. Non-limiting examples of PDMS
polymers include those sold under the trademark Sylgard by Dow
Chemical Co., Midland, Mich., and particularly Sylgard 182, Sylgard
184, and Sylgard 186. Silicone polymers including PDMS have several
beneficial properties simplifying formation of the microfluidic
structures of the invention. For instance, such materials are
inexpensive, readily available, and can be solidified from a
prepolymeric liquid via curing with heat. For example, PDMSs are
typically curable by exposure of the prepolymeric liquid to
temperatures of about, for example, about 65.degree. C. to about
75.degree. C. for exposure times of, for example, about an hour.
Also, silicone polymers, such as PDMS, can be elastomeric and thus
may be useful for forming very small features with relatively high
aspect ratios, necessary in certain embodiments of the invention.
Flexible (e.g., elastomeric) molds or masters can be advantageous
in this regard.
[0079] The present invention provides improved methods of bonding
PDMS to incompatible media. Normal methods of bonding various
materials (plastic, metals, etc) directly to materials such as
PDMS, silicone, Teflon, and PEEK using traditional bonding
practices (adhesives, epoxies, etc) do not Work well due to the
poor adhesion of the bonding agent to materials such as PDMS.
Normal surface preparation by commercially available surface
activators has not worked well in microfluidic device
manufacturing. This problem is eliminated by treating the PDMS
surface to be bonded with high intensity oxygen or air plasma. The
process converts the top layer of PDMS to glass which bonds
extremely well with normal adhesives. Tests using this method to
bond external fluid lines to PDMS using a UV-cure adhesive (Loctite
352, 363, and others) resulted in a bond that is stronger than the
PDMS substrate, resulting in fracture of the PDMS prior to failure
of the bond. The present method combines high radiant flux,
wavelength selection, and cure exposure time to significantly
enhance the bond strength of the adhesive.
[0080] One advantage of forming structures such as microfluidic
structures of the invention from silicone polymers, such as PDMS,
is the ability of such polymers to be oxidized, for example by
exposure to an oxygen-containing plasma such as an air plasma, so
that the oxidized structures contain, at their surface, chemical
groups capable of cross-linking to other oxidized silicone polymer
surfaces or to the oxidized surfaces of a variety of other
polymeric and non-polymeric materials. Thus components can be
formed and then oxidized and essentially irreversibly sealed to
other silicone polymer surfaces, or to the surfaces of other
substrates reactive with the oxidized silicone polymer surfaces,
without the need for separate adhesives or other sealing means. In
most cases, sealing can be completed simply by contacting an
oxidized silicone surface to another surface without the need to
apply auxiliary pressure to form the seal. That is, the
pre-oxidized silicone surface acts as a contact adhesive against
suitable mating surfaces. Specifically, in addition to being
irreversibly sealable to itself, oxidized silicone such as oxidized
PDMS can also be sealed irreversibly to a range of oxidized
materials other than itself including, for example, glass, silicon,
silicon oxide, quartz, silicon nitride, polyethylene, polystyrene,
glassy carbon, and epoxy polymers, which have been oxidized in a
similar fashion to the PDMS surface (for example, via exposure to
an oxygen-containing plasma). methods useful in the context of the
present invention, as well as overall molding techniques, are
described in the art, for example, in an article entitled "Rapid
Prototyping of Microfluidic Systems and Polydimethylsiloxane,"
Anal. Chem., 70:474-480, 1998 (Duffy et al.), incorporated herein
by reference.
[0081] Another advantage to forming microfluidic structures of the
invention (or interior, fluid contacting surfaces) from oxidized
silicone polymers is that these surfaces can be much more
hydrophilic than the surfaces of typical elastomeric polymers
(where a hydrophilic interior surface is desired). Such hydrophilic
channel surfaces can thus be more easily filled and wetted with
aqueous solutions than can structures comprised of typical,
unoxidized elastomeric polymers or other hydrophobic materials.
[0082] In one embodiment, a bottom wall is formed of a material
different from one or more side walls or a top wall, or other
components. For example, the interior surface of a bottom wall can
comprise the surface of a silicon wafer or microchip, or other
substrate. Other components can, as described above, be sealed to
such alternative substrates. Where it is desired to seal a
component comprising a silicone polymer (e.g. PDMS) to a substrate
(bottom wall) of different material, the substrate may be selected
from the group of materials to which oxidized silicone polymer is
able to irreversibly seal (e.g., glass, silicon, silicon oxide,
quartz, silicon nitride, polyethylene, polystyrene, epoxy polymers,
and glassy carbon surfaces which have been oxidized).
Alternatively, other sealing techniques can be used, as would be
apparent to those of ordinary skill in the art, including, but not
limited to, the use of separate adhesives, thermal bonding, solvent
bonding, ultrasonic welding, etc.
Channels
[0083] The microfluidic substrates of the present invention include
channels that form the boundary for a fluid. A "channel," as used
herein, means a feature on or in a substrate that at least
partially directs the flow of a fluid. In some cases, the channel
may be formed, at least in part, by a single component, e.g., an
etched substrate or molded unit. The channel can have any
cross-sectional shape, for example, circular, oval, triangular,
irregular, square or rectangular (having any aspect ratio), or the
like, and can be covered or uncovered (i.e., open to the external
environment surrounding the channel). In embodiments where the
channel is completely covered, at least one portion of the channel
can have a cross-section that is completely enclosed, and/or the
entire channel may be completely enclosed along its entire length
with the exception of its inlet and outlet.
[0084] An open channel generally will include characteristics that
facilitate control over fluid transport, e.g., structural
characteristics (an elongated indentation) and/or physical or
chemical characteristics (hydrophobicity vs. hydrophilicity) and/or
other characteristics that can exert a force (e.g., a containing
force) on a fluid. The fluid within the channel may partially or
completely fill the channel. In some cases the fluid may be held or
confined within the channel or a portion of the channel in some
fashion, for example, using surface tension (e.g., such that the
fluid is held within the channel within a meniscus, such as a
concave or convex meniscus). In an article or substrate, some (or
all) of the channels may be of a particular size or less, for
example, having a largest dimension perpendicular to fluid flow of
less than about 5 mm, less than about 2 mm, less than about 1 mm,
less than about 500 microns, less than about 200 microns, less than
about 100 microns, less than about 60, less than about 50 microns,
less than about 40 microns, less than about 30 microns, less than
about 25 microns, less than about 10 microns, less than about 3
microns, less than about 1 micron, less than about 300 nm, less
than about 100 nm, less than about 30 nm, or less than about 10 nm
or less in some cases. Of course, in some cases, larger channels,
tubes, etc. can be used to store fluids in bulk and/or deliver a
fluid to the channel. In one embodiment, the channel is a
capillary.
[0085] The dimensions of the channel may be chosen such that fluid
is able to freely flow through the channel, for example, if the
fluid contains cells. The dimensions of the channel may also be
chosen, for example, to allow a certain volumetric or linear flow
rate of fluid in the channel. Of course, the number of channels and
the shape of the channels can be varied by any method known to
those of ordinary skill in the art. In some cases, more than one
channel or capillary may be used. For example, two or more channels
may be used, where they are positioned inside each other,
positioned adjacent to each other, etc.
[0086] For particles (e.g., cells) or molecules that are in
droplets (i.e., deposited by the inlet module) within the flow of
the main channel, the channels of the device are preferably square,
with a diameter between about 2 microns and 1 mm. This geometry
facilitates an orderly flow of droplets in the channels. Similarly,
the volume of the detection module in an analysis device is
typically in the range of between about 0.1 picoliters and 500
nanoliters.
[0087] A "main channel" is a channel of the device of the invention
which permits the flow of molecules, cells, small molecules or
particles past a coalescence module for coalescing one or more
droplets, a detection module for detection (identification) or
measurement of a droplet and a sorting module, if present, for
sorting a droplet based on the detection in the detection module.
The main channel is typically in fluid communication with the
coalescence, detection and/or sorting modules, as well as, an inlet
channel of the inlet module. The main channel is also typically in
fluid communication with an outlet module and optionally with
branch channels, each of which may have a collection module or
waste module. These channels permit the flow of molecules, cells,
small molecules or particles out of the main channel. An "inlet
channel" permits the flow of molecules, cells, small molecules or
particles into the main channel. One or more inlet channels
communicate with one or more means for introducing a sample into
the device of the present invention. The inlet channel communicates
with the main channel at an inlet module.
[0088] The microfluidic substrate can also comprise one or more
fluid channels to inject or remove fluid in between droplets in a
droplet stream for the purpose of changing the spacing between
droplets.
[0089] The channels of the device of the present invention can be
of any geometry as described. However, the channels of the device
can comprise a specific geometry such that the contents of the
channel are manipulated, e.g., sorted, mixed, prevent clogging,
etc.
[0090] A microfluidic substrate can also include a specific
geometry designed in such a manner as to prevent the aggregation of
biological/chemical material and keep the biological/chemical
material separated from each other prior to encapsulation in
droplets. The geometry of channel dimension can be changed to
disturb the aggregates and break them apart by various methods,
that can include, but is not limited to, geometric pinching (to
force cells through a (or a series of) narrow region(s), whose
dimension is smaller or comparable to the dimension of a single
cell) or a barricade (place a series of barricades on the way of
the moving cells to disturb the movement and break up the
aggregates of cells).
[0091] To prevent material (e.g., cells and other particles or
molecules) from adhering to the sides of the channels, the channels
(and coverslip, if used) may have a coating which minimizes
adhesion. Such a coating may be intrinsic to the material from
which the device is manufactured, or it may be applied after the
structural aspects of the channels have been microfabricated.
"TEFLON" is an example of a coating that has suitable surface
properties. The surface of the channels of the microfluidic device
can be coated with any anti-wetting or blocking agent for the
dispersed phase. The channel can be coated with any protein to
prevent adhesion of the biological/chemical sample. For example, in
one embodiment the channels are coated with BSA, PEG-silane and/or
fluorosilane. For example, 5 mg/ml BSA is sufficient to prevent
attachment and prevent clogging. In another embodiment, the
channels can be coated with a cyclized transparent optical polymer
obtained by copolymerization of perfluoro (alkenyl vinyl ethers),
such as the type sold by Asahi Glass Co. under the trademark Cytop.
In such an embodiment, the coating is applied from a 0.1-0.5 wt %
solution of Cytop CTL-809M in CT-Solv 180. This solution can be
injected into the channels of a microfluidic device via a plastic
syringe. The device can then be heated to about 90.degree. C. for 2
hours, followed by heating at 200.degree. C. for an additional 2
hours. In another embodiment, the channels can be coated with a
hydrophobic coating of the type sold by PPG Industries, Inc. under
the trademark Aquapel (e.g., perfluoroalkylsilane surface treatment
of plastic and coated plastic substrate surfaces in conjunction
with the use of a silica primer layer) and disclosed in U.S. Pat.
No. 5,523,162, which patient is hereby incorporated by reference.
By fluorinating the surfaces of the channels, the continuous phase
preferentially wets the channels and allows for the stable
generation and movement of droplets through the device. The low
surface tension of the channel walls thereby minimizes the
accumulation of channel clogging particulates.
[0092] The surface of the channels in the microfluidic device can
be also fluorinated to prevent undesired wetting behaviors. For
example, a microfluidic device can be placed in a polycarbonate
dessicator with an open bottle of
(tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane. The
dessicator is evacuated for 5 minutes, and then sealed for 20-40
minutes. The dessicator is then backfilled with air and removed.
This approach uses a simple diffusion mechanism to enable facile
infiltration of channels of the microfluidic device with the
fluorosilane and can be readily scaled up for simultaneous device
fluorination.
Fluids
[0093] The microfluidic device Of the present invention is capable
of controlling the direction and flow of fluids and entities within
the device. The term "flow" means any movement of liquid or solid
through a device or in a method of the invention, and encompasses
without limitation any fluid stream, and any material moving with,
within or against the stream, whether or not the material is
carried by the stream. For example, the movement of molecules,
beads, cells or virions through a device or in a method of the
invention, e.g. through channels of a microfluidic chip of the
invention, comprises a flow. This is so, according to the
invention, whether or not the molecules, beads, cells or virions
are carried by a stream of fluid also comprising a flow, or whether
the molecules, cells or virions are caused to move by some other
direct or indirect force or motivation, and whether or not the
nature of any motivating force is known or understood. The
application of any force may be used to provide a flow, including
without limitation, pressure, capillary action, electro-osmosis,
electrophoresis, dielectrophoresis, optical tweezers, and
combinations thereof, without regard for any particular theory or
mechanism of action, so long as molecules, cells or virions are
directed for detection, measurement or sorting according to the
invention. Specific flow forces are described in further detail
herein.
[0094] The flow stream in the main channel is typically, but not
necessarily, continuous and may be stopped and started, reversed or
changed in speed. A liquid that does not contain sample molecules,
cells or particles can be introduced into a sample inlet well or
channel and directed through the inlet module, e.g., by capillary
action, to hydrate and prepare the device for use. Likewise, buffer
or oil can also be introduced into a main inlet region that
communicates directly with the main channel to purge the device
(e.g., or "dead" air) and prepare it for use. If desired, the
pressure can be adjusted or equalized, for example, by adding
buffer or oil to an outlet module.
[0095] As used herein, the term "fluid stream" or "fluidic stream"
refers to the flow of a fluid, typically generally in a specific
direction. The fluidic stream may be continuous and/or
discontinuous. A "continuous" fluidic stream is a fluidic stream
that is produced as a single entity, e.g., if a continuous fluidic
stream is produced from a channel, the fluidic stream, after
production, appears to be contiguous with the channel outlet. The
continuous fluidic stream is also referred to as a continuous phase
fluid or carrier fluid. The continuous fluidic stream may be
laminar, or turbulent in some cases.
[0096] Similarly, a "discontinuous" fluidic stream is a fluidic
stream that is not produced as a single entity. The discontinuous
fluidic stream is also referred to as the dispersed phase fluid or
sample fluid. A discontinuous fluidic stream may have the
appearance of individual droplets, optionally surrounded by a
second fluid. A "droplet," as used herein, is an isolated portion
of a first fluid that completely surrounded by a second fluid. In
some cases, the droplets may be spherical or substantially
spherical; however, in other cases, the droplets may be spherical
or substantially spherical; however, in other cases, the droplets
may be non-spherical, for example, the droplets may have the
appearance of "blobs" or other irregular shapes, for instance,
depending on the external environment. As used herein, a first
entity is "surrounded" by a second entity if a closed loop can be
drawn or idealized around the first entity through only the second
entity. The dispersed phase fluid can include a biological/chemical
material. The biological/chemical material can be tissues, cells,
particles, proteins, antibodies, amino acids, nucleotides, small
molecules, and pharmaceuticals. The biological/chemical material
can include one or more labels known in the art. The label can be a
DNA tag, dyes or quantum dot, or combinations thereof.
[0097] Droplets
[0098] The term "emulsion" refers to a preparation of one liquid
distributed in small globules (also referred to herein as drops,
droplets or NanoReactors) in the body of a second liquid. The first
and second fluids are immiscible with each other. For example, the
discontinuous phase can be an aqueous solution and the continuous
phase can a hydrophobic fluid such as an oil. This is termed a
water in oil emulsion. Alternatively, the emulsion may be a oil in
water emulsion. In that example, the first liquid, which is
dispersed in globules, is referred to as the discontinuous phase,
whereas the second liquid, is referred to as the continuous phase
or the dispersion medium. The continuous phase can be an aqueous
solution and the discontinuous phase is a hydrophobic fluid, such
as an oil (e.g., decane, tetradecane, or hexadecane). The droplets
or globules of oil in an oil in water emulsion are also referred to
herein as "micelles", whereas globules of water in a water in oil
emulsion may be referred to as "reverse micelles".
[0099] The fluidic droplets may each be substantially the same
shape and/or size. The shape and/or size can be determined, for
example, by measuring the average diameter or other characteristic
dimension of the droplets. The "average diameter" of a plurality or
series of droplets is the arithmetic average of the average
diameters of each of the droplets. Those of ordinary skill in the
art will be able to determine the average diameter (or other
characteristic dimension) of a plurality or series of droplets, for
example, using laser light scattering, microscopic examination, or
other known techniques. The diameter of a droplet, in a
non-spherical droplet, is the mathematically-defined average
diameter of the droplet, integrated across the entire surface. The
average diameter of a droplet (and/or of a plurality or series of
droplets) may be, for example, less than about 1 mm, less than
about 500 micrometers, less than about 200 micrometers, less than
about 100 micrometers, less than about 75 micrometers, less than
about 50 micrometers, less than about 25 micrometers, less than
about 10 micrometers, or less than about 5 micrometers in some
cases. The average diameter may also be at least about 1
micrometer, at least about 2 micrometers, at least about 3
micrometers, at least about 5 micrometers, at least about 10
micrometers, at least about 15 micrometers, or at least about 20
micrometers in certain cases.
[0100] As used herein, the term "NanoReactor" and its plural
encompass the terms "droplet", "nanodrop", "nanodroplet",
"microdrop" or "microdroplet" as defined herein, as well as an
integrated system for the manipulation and probing of droplets, as
described in detail herein. Nanoreactors as described herein can be
0.1-1000 .mu.m (e.g., 0.1, 0.2 . . . 5, 10, 15, 20, 25, 30, 35, 40,
45, 50 . . . 1000), or any size within in this range. Droplets at
these dimensions tend to conform to the size and shape of the
channels, while maintaining their respective volumes. Thus, as
droplets move from a wider channel to a narrower channel they
become longer and thinner, and vice versa.
[0101] The microfluidic substrate of this invention most preferably
generate round, monodisperse droplets. The droplets can have a
diameter that is smaller than the diameter of the microchannel;
i.e., preferably 15 to 100 .mu.m when cells are used; or 10 to 75
.mu.m when reagents or other chemical or biological agents are
used; or 100 to 1000 .mu.m when droplets are used for sequencing
reactions such that droplets will be removed and dispensed into
other collection apparatuses, such as microtiter plates or utilized
in sequencing devices. Monodisperse droplets are particularly
preferably, e.g., in high throughput devices and other embodiments
where it is desirable to generate droplets at high frequency and of
high uniformity.
[0102] The droplet forming liquid is typically an aqueous buffer
solution, such as ultrapure water (e.g., 18 mega-ohm resistivity,
obtained, for example by column chromatography), 10 mM Tris HC1 and
1 mM EDTA (TE) buffer, phosphate buffer saline (PBS) or acetate
buffer. Any liquid or buffer that is physiologically compatible
with the population of molecules, cells or particles to be analyzed
and/or sorted can be used. The fluid passing through the main
channel and in which the droplets are formed is one that is
immiscible with the droplet forming fluid. The fluid passing
through the main channel can be a non-polar solvent, decane (e.g.,
tetradecane or hexadecane), fluorocarbon oil, silicone oil or
another oil (for example, mineral oil).
[0103] The dispersed phase fluid may also contain
biological/chemical material (e.g., molecules, cells or other
particles) for combination, analysis and/or sorting in the device.
The droplets of the dispersed phase fluid can contain more than one
particle or can contain no more than one particle. For example,
where the biological material comprises cells, each droplet
preferably contains, on average, no more than one cell. However, in
some embodiments, each droplet may contain, on average, at least
1000 cells. The droplets can be detected and/or sorted according to
their contents.
[0104] The concentration (i.e., number) of molecules, cells or
particles in a droplet can influence sorting efficiently and
therefore is preferably optimized. In particular, the sample
concentration should be dilute enough that most of the droplets
contain no more than a single molecule, cell or particle, with only
a small statistical chance that a droplet will contain two or more
molecules, cells or particles. This is to ensure that for the large
majority of measurements, the level of reporter measured in each
droplet as it passes through the detection module corresponds to a
single molecule, cell or particle and not to two or more molecules,
cells or particles.
[0105] The parameters which govern this relationship are the volume
of the droplets and the concentration of molecules, cells or
particles in the sample solution. The probability that a droplet
will contain two or more molecules, cells or particles
(P.sub..ltoreq.2) can be expressed as
P.sub..ltoreq.2=1-{1+[cell]xV}x e.sup.-[cell]x V
[0106] where "[cell]" is the concentration of molecules, cells or
particles in units of number of molecules, cells or particles per
cubic micron (.mu.m.sup.3), and V is the volume of the droplet in
units of .mu.m.sup.3.
[0107] It will be appreciated that P.sub..ltoreq.2 can be minimized
by decreasing the concentration of molecules, cells or particles in
the sample solution. However, decreasing the concentration of
molecules, cells or particles in the sample solution also results
in an increased volume of solution processed through the device and
can result in longer run times. Accordingly, it is desirable to
minimize to presence of multiple molecules, cells or particles in
the droplets (thereby increasing the accuracy of the sorting) and
to reduce the volume of sample, thereby permitting a sorted sample
in a reasonable time in a reasonable volume containing an
acceptable concentration of molecules, cells or particles.
[0108] The maximum tolerable P.sub..ltoreq.2 depends on the desired
"purity" of the sorted sample. The "purity" in this case refers to
the fraction of sorted molecules, cells or particles that posses a
desired characteristic (e.g., display a particular antigen, are in
a specified size range or are a particular type of molecule, cell
or particle). The purity of the sorted sample is inversely
proportional to P.sub..ltoreq.2. For example, in applications where
high purity is not needed or desired a relatively high
P.sub..ltoreq.2 (e.g., P.sub..ltoreq.2=0.2) may be acceptable. For
most applications, maintaining P.sub..ltoreq.2 at or below about
0.1, preferably at or below about 0.01, provides satisfactory
results.
[0109] The fluids used to generate droplets in microfluidic devices
are typically immiscible liquids such as oil and water. These two
materials generally have very different dielectric constants
associated with them. These differences can be exploited to
determine droplet rate and size for every drop passing through a
small section of a microfluidic device. One method to directly
monitor this variation in the dielectric constant measures the
change in capacitance over time between a pair of closely spaced
electrodes. This change in capacitance can be detected by the
change in current measured in these electrodes:
i = V dC dt ##EQU00001##
[0110] Where i is the current, V is the voltage applied across the
electrodes, and dC/dt is the change in capacitance with time.
Alternatively, the capacitance can be measured directly if a time
varying voltage is applied to these same electrodes: i=CdV/dt Where
C is the measured capacitance, and dV/dt is the change in voltage
with time. As a first approximation, the electrode pair can be
determined as a parallel plate capacitor:
C = 0 k A d ##EQU00002##
[0111] Where .di-elect cons..sub.0 is the permittivity of free
space, k is the effective dielectric constant (this changes every
time a droplet passes through), A is the area of the capacitor and
d is the electrode separation. The current measured in the device
is then plotted as a function of time.
[0112] The fluidic droplets may contain additional entities, for
example, other chemical, biochemical, or biological entities (e.g.,
dissolved or suspended in the fluid), cells, particles, gases,
molecules, or the like. In some cases, the droplets may each be
substantially the same shape or size, as discussed above. In
certain instances, the invention provides for the production of
droplets consisting essentially of a substantially uniform number
of entities of a species therein (i.e., molecules, cells,
particles, etc.). For example, about 90%, about 93%, about 95%,
about 97%, about 98%, or about 99%, or more of a plurality or
series of droplets may each contain the same number of entities of
a particular species. For instance, a substantial number of fluidic
droplets produced, e.g., as described above, may each contain 1
entity, 2 entities, 3 entities, 4 entities, 5 entities, 7 entities,
10 entities, 15 entities, 20 entities, 25 entities, 30 entities, 40
entities, 50 entities, 60 entities, 70 entities, 80 entities, 90
entities, 100 entities, etc., where the entities are molecules or
macromolecules, cells, particles, etc. In some cases, the droplets
may each independently contain a range of entities, for example,
less than 20 entities, less than 15 entities, less than 10
entities, less than 7 entities, less than 5 entities, or less than
3 entities in some cases. In some embodiments, a droplet may
contain 100,000,000 entities. In other embodiments, a droplet may
contain 1,000,000 entities.
[0113] In a liquid containing droplets of fluid, some of which
contain a species of interest and some of which do not contain the
species of interest, the droplets of fluid may be screened or
sorted for those droplets of fluid containing the species as
further described below (e.g., using fluorescence or other
techniques such as those described above), and in some cases, the
droplets may be screened or sorted for those droplets of fluid
containing a particular number or range of entities of the species
of interest, e.g., as previously described. Thus, in some cases, a
plurality or series of fluidic droplets, some of which contain the
species and some of which do not, may be enriched (or depleted) in
the ratio of droplets that do contain the species, for example, by
a factor of at least about 2, at least about 3, at least about 5,
at least about 10, at least about 15, at least about 20, at least
about 50, at least about 100, at least about 125, at least about
150, at least about 200, at least about 250, at least about 500, at
least about 750, at least about 1000, at least about 2000, or at
least about 5000 or more in some cases. In other cases, the
enrichment (or depletion) may be in a ratio of at least about
10.sup.4, at least about 10.sup.5, at least about 10.sup.6, at
least about 10.sup.7, at least about 10.sup.8, at least about
10.sup.9, at least about 10.sup.10, at least about 10.sup.11, at
least about 10.sup.12; at least about 10.sup.13, at least about
10.sup.14, at least about 10.sup.15, or more. For example, a
fluidic droplet containing a particular species may be selected
from a library of fluidic droplets containing various species,
where the library may have about 100, about 10.sup.3, about
10.sup.4, about 10.sup.5, about 10.sup.6, about 10.sup.7, about
10.sup.8, about 10.sup.9, about 10.sup.10, about 10.sup.11, about
10.sup.12, about 10.sup.13, about 10.sup.14, about 10.sup.15, or
more items, for example, a DNA library, an RNA library, a protein
library, a combinatorial chemistry library, etc. In certain
embodiments, the droplets carrying the species may then be fused,
reacted, or otherwise used or processed, etc., as further described
below, for example, to initiate or determine a reaction.
[0114] Droplets of a sample fluid can be formed within the inlet
module on the microfluidic device or droplets (or droplet
libraries) can be formed before the sample fluid is introduced to
the microfluidic device ("off chip" droplet formation). To permit
effective interdigitation, coalescence and detection, the droplets
comprising each sample to be analyzed must be monodisperse. As
described in more detail herein, in many applications, different
samples to be analyzed are contained within droplets of different
sizes. Droplet size must be highly controlled to ensure that
droplets containing the correct contents for analysis and coalesced
properly. As such, the present invention provides devices and
methods for forming droplets and droplet libraries.
[0115] Devices and Methods for Forming Sample Droplets on a
Microfluidic Substrate
[0116] The present invention provides compositions and methods for
forming sample droplet emulsions on a microfluidic substrate. The
present invention also provides embedded microfluidic nozzles. In
order to create a monodisperse emulsion directly from a library
well, this invention would form a nozzle directly into the fitting
used to connect the storage well/reservoir (e.g. syringe) to a
syringe tip (e.g. capillary tubing), as shown in FIGS. 2-6. FIG. 2,
Panels A and B, show dual and single oil versions of the nozzle
concept using a small ferrule for the nozzle section. FIG. 2,
Panels C and D, show the same Nozzles made directly out of small
bore tubing (the "nozzle" runs the entire length of the tubing).
Both designs can form droplets identically, although the pressure
drop will be higher for the tube based nozzle (bottom). FIG. 3
shows the expansion of the nozzle ferrule concept shown in FIGS. 2A
and 2B. The tube based nozzles (FIG. 2C, 2D) function identically
to this, except the "nozzle" runs the entire length of the tube
instead of having a short transition. The ability to form droplets
is identical in both cases. FIG. 4 shows the expansion of the
nozzle section contained in the ferrule. The tee design in FIG. 2D
has been built and tested, with a cross-section cut of this design
shown in FIG. 5. FIG. 5A shows the operation of the nozzle in
Aspiration Mode and FIG. 5B shows the operation of the nozzle in
Injection Mode. The droplets formed are approximately 45 um in
diameter, and were formed from PCR mix (210 ul/hr) and
SpectraSyn-10 (600 ul/hr). Other tests have been demonstrated with
Spectrasyn-2 and PCR. mix. The droplets are traveling in 300 um
wide.times.260 um deep channels. The Nozzle tube used was 100 um in
diameter, and the fluids used were PCR Mix and Spectrasyn-10 with
surfactant.
[0117] Since the flow is three dimensional, under this design
surface wetting effects are minimized. The nozzle can be made from
one or two oil lines providing constant flow of oil into the
nozzle, a connection to the capillary tubing, and a connection to
the storage well/reservoir (e.g. syringe). The high resolution part
of the nozzle can be made out of a small bore tubing or a small,
simple part molded or stamped from an appropriate material
(Teflon.RTM., plastic, metal, etc). If necessary, the nozzle itself
could be formed into the tip of the ferrule using post mold
processing such as laser ablation or drilling.
[0118] This nozzle design eliminates the surface wetting issues
surrounding the quasi-2D flow associated with typical microfluidic
nozzles made using soft lithography or other standard microfluidic
chip manufacturing techniques. This is because the nozzle design is
fully 3-dimensional, resulting is a complete isolation of the
nozzle section from the continuous aqueous phase. This same design
can also be used for generation of emulsions required for immediate
use, where the aqueous line would be attached directly to a syringe
and the outlet of the nozzle would be used to transport the
emulsion to the point of use (e.g. into a microfluidic PCR chip,
delay line, etc).
[0119] In another embodiment, the present invention provides
compositions and methods to directly emulsify library elements from
standard library storage geometries (e.g. 96 well plates, etc). In
order to create a monodisperse emulsion from fluids contained in a
library well plate, this invention would include microfluidic based
nozzles manufactured simultaneously with an appropriately designed
fluidic interconnect or well. FIGS. 6 and 7 present two possible
approaches to interface with the nozzle.
[0120] FIG. 6 shows a reservoir based sample emulsification. In
FIG. 6, the well is initially filled with a fluid with lower
density than the sample to be introduced. The operation of this
device would be very similar to the device described above, with
the exception that the sample would be introduced into a port
instead of being directly aspirated from a sample well. This could
either be emulsification oil obtained directly from the nozzle, or
a different material that is loaded or flowing into the well
automatically. The oil lines would begin flowing at their
prescribed rates (FIG. 6e), while the collection or waste port
would begin withdrawing at a rate corresponding to the total oil
flow plus the desired sample flow. Once the flow has been
established, the sample would be introduced into the port either
manually (e.g. a pipette) or with a robotic sample handling system.
The sample volume permitted would be dependent on the port volume.
Since the sample is more dense than the fluid in the well, it would
settle into the bottom of the well and be transported to the nozzle
(FIGS. 6a-6d). During this time, either the waste (used during
startup only if transients cause problems) or the collection port
would be withdrawing emulsified sample and stored. When the sample
is completely emulsified the next sample would be introduced and
the process repeated. If washing steps are required between runs,
the washing fluids would be withdrawn into the waste line. If the
pressure drop across the nozzle would cause cavitation on
collection then an optional pressurization of the input well can be
utilized.
[0121] FIG. 7 shows sample introduction when the sample is less
dense than the fluid in the sample port. FIG. 7 depicts an
alternative scheme that could be used to introduce samples that are
less dense than the oil used to emulsify the sample. As with the
concept in FIG. 1, the process of introducing the sample into the
port could be run either manually or with a robotic sampling
system. In this concept, the sample port could be filled with the
emulsification oil through backflow from the nozzle prior to
introduction of the sample (FIG. 7a). If this oil is not
appropriate, the port can be filled from the top with a different
immiscible fluid that might have more desirable properties than the
emulsification oil (e.g. better wetting, less surfactant, etc).
This second immiscible fluid could be introduced during startup and
flow continuously into the port when the sample tip is not
inserted. Keeping the sample port filled with fluid will prevent
air entrainment during startup and should improve transient
performance.
[0122] If the sample tip is connected to a pump capable of driving
the sample into the device, it could be started up as the tip is
inserted into the device (7b-c). When used with this sort of sample
introduction, the device could be run identically to the "normal"
operation of our devices, including having the "transport to waste"
line (7e) not connected to a pump. If the sample tip loading pump
is not capable of accurately forcing the flow (i.e. not connected
to a suitable pump), the back end of the tip could be connected to
a valve that would open to either atmospheric pressure (or possibly
a pressurized gas supply) when the tip is fully inserted into the
port. In order to prevent air entrainment into the sample tip and
device, this connection could be made through a reservoir filled
with the desired immiscible liquid. In either case, the device
would run identically to the one described above and shown in FIG.
6. FIG. 7 also shows another possible configuration of the
aspiration probe assembly used for the device in FIG. 6.
[0123] Methods for Forming Sample Droplet Emulsions Prior to
Injection on a Microfluidic Substrate
[0124] The present invention also provides compositions and methods
for creating emulsion of the sample fluid (e.g. droplets) prior to
the introduction of the sample fluid into the microfluidic devices
of the present invention. More specifically, the methods are
directed to the creating sample droplet emulsions "off chip", for
example in a syringe. In order to create a monodisperse emulsion
directly from a library well, a nozzle is formed directly into the
fitting used to connect the collection syringe to a syringe tip
(e.g. capillary tubing), as shown in FIG. 8. The nozzle can be made
from one or two oil lines providing constant flow of oil into the
nozzle, a connection to the capillary tubing, and a connection to
the collection syringe. Aspiration of the sample can be
accomplished by running the collection syringe in withdrawal mode
at a flow rate (Q3) above the flow rate of the two oil syringes
(Step 1 in FIG. 8). The difference in flow would correspond to the
flow rate aspirated from the sample well. When the appropriate
volume of sample has been loaded into the capillary tubing, the
capillary tubing would be removed from the sample well, an air
bubble, and possibly a cleaning solution would be aspirated (Step 2
in FIG. 8). When almost all of the sample has been emulsified, the
collection syringe withdrawal rate would either be reduced below
the oil flow rates, stopped, or set to infuse at some nominal rate
(Step 3 in FIG. 8). The remaining sample, air, cleaning solution,
etc, left in the capillary would be flushed back out into a
cleaning well and the outside of the capillary would be cleaned at
the "wash station." When the capillary is completely clean, the
process would repeat for the next library element.
[0125] The nozzle can be formed through using small bore tubing
(glass, Teflon.RTM., PEEK tubing or capillaries) or
micro-fabrication or molding processes such as PDMS soft
lithography, glass etching, hot embossing, or similar high
resolution fabrication technology.
[0126] The present apparatus can be readily adapted for clinical
applications or work where cross contamination must be eliminated,
since the region from the nozzle to the syringe are isolated from
the sample stream (e.g., the oil wets these surfaces and keeps the
sample from directly contacting aqueous sample). The aspiration tip
can be designed as a disposable item (like a robotic sampler
aspiration tips) and automatically replaced between samples.
[0127] Multiple nozzle/syringe pairs can be operated in parallel,
thus increasing throughput. This allows simultaneous sampling of
multiple wells/samples during a single process step. Each sample
can be collected into a separate syringe.
[0128] Other methods for forming sample droplet emulsions and
emulsion libraries "off chip" are described in Example 1.
[0129] Methods for Minimizing Sample Volume Loss
[0130] As described herein, a significant problem when working with
very small amounts of reagents comes from the losses associated
with dead volumes found in the storage containers and transport
lines. As an example, if 50 microliters of a material is injected
into a 254 micron internal diameter capillary tube, a 75 cm long
tube would consume about 38 microliters of the material
(.about.75%). To address this problem, the present invention
provides compositions and methods which eliminates the problems
associated with dead volume and reagent waste when working with
extremely small volumes of reagents.
[0131] In one embodiment, the primary reagents (sample) is combined
with a second, immiscible phase in the storage container (e.g. a
syringe or other reservoir). This second phase is used to push the
entire amount of the first phase into the system with no
significant losses. More specifically, when two immiscible fluids
are combined in a reservoir, the two fluids will tend to separate
into layers as long as the densities of the materials are
different. If the fluid of interest (e.g., sample fluid) is closest
to the exit of the reservoir, it will be the first to leave when
the reservoir is emptied (the exit can be on either the top or
bottom, depending on the density difference). Once the reagent has
been pumped out of the reservoir, the second phase will follow.
This second phase will then push the first phase completely through
the system without any sample fluid loss. As an example of this,
oil and water (the reagent) would be combined in a syringe. If the
oil is denser than the water, the syringe would be oriented with
its exit face up, if the oil were less dense, then the syringe
would be face down. The oil would be chosen such that the materials
of interest in the reagent are not soluble in the oil phase. FIG. 9
is one example of this approach when a syringe is used as the
reservoir and the second phase is denser than the reagent phase. If
the reagent were more dense, then the syringe orientation would be
reversed (i.e. the exit would be facing downward in the figure).
Specifically, FIG. 9 shows a two phase system where the reagent is
injected on top of the second, immiscible phase: (A) During
injection, prior to transition from first phase to second phase,
(B) second phase just entering the transfer line, (C) second phase
has completely filled the transfer line and pushed the entire
volume of reagent through the system.
[0132] Alternatively, a sample solution is sandwiched between two
immiscible liquids, wherein one liquid has a density greater than
the sample density, and the second liquid has a density less than
the sample density. Referring to FIG. 10, the sample (density 1.0)
can be layered between perfluorocarbon oil (density 1.8) and
mineral oil (density 0.914). Ideally, when the device is being used
to analyze biological reactions the immiscible solutions do not
inhibit the reactions of the sample, nor are any test molecules in
the sample or the sample itself soluble in either immiscible fluid.
The less dense fluid (in FIG. 10, the mineral oil) can be used to
`prime the pump` and remove any air or dead-space that occurs
during normal injection. The sample then rises to the injection
point after the mineral oil. It is further contemplated that the
methods disclosed herein would also work for gases. The gases
and/or liquids can be miscible, but of different densities such
that they are layered on top each other in a manner that prevents
their mixing.
[0133] Solid or Semi-Solid Phase Droplets
[0134] The present invention also provides solid phase particles
and methods for the forming solid phase particles on a microfluidic
device for downstream analysis. The solid phase particles can be
used for various biological or chemical analysis (e.g., DNA or
protein analyses).
[0135] For DNA analysis, post amplification encapsulation of
amplicons occurs within a gel or polymer matrix prior to breaking
of the droplet emulsion. Amplification reactions within droplets
using one of several amplification type methods (described in
further detail herein), including, but not limited to; PCR, Rolling
Circle Amplification (RCA), Nucleic Acid Sequence Based
Amplification (NASBA), ligase chain reaction, etc. followed by
encapsulation/solidification of the amplified reaction within the
droplets by either polymerizing the droplets using chemical or
physical means.
[0136] A physical means might be termed `gelling` whereby one
incorporates low temperature agarose within the droplet during
formulation and keeping the droplet above the solidification
temperature until one desires the droplet to solidify.
[0137] A chemical means might be termed `polymerization` whereby
one combines (if needed) the droplet with a polymerizing solution
and then polymerizing the droplet using either a polymerization
initiator (for example free radicals) or a means such as UV light.
Some other means of gelling or polymerization include matragel,
polyacrylamide, mixed polysaccharides, etc. Some example initiators
can be temperature, UV irradiation, etc.
[0138] In a further example, one of the DNA primers used for
amplification can be attached to one of the molecules that will
form the polymerized matrix. Attachment can be through a direct
chemical attachment, or through a secondary attachment such as
biotin-streptavidin attachment. In this example, the DNA will
become physically attached to the formed solid-phase that occurs
after solidification of the droplet. Using one of several gelling
or polymerizing methods it should be possible to further manipulate
these droplets.
[0139] One could also either exchange or wash away unincorporated
nucleotides, primers and exchange buffers so as to remove the
initial amplification buffers, polymerases, etc. In an example of
further droplet manipulation wherein one of the strands is
polymerized from an attached DNA amplification primer, one could
treat the polymerized or gelled droplet with a base solution to
disassociate the two DNA strands and elute, from the gelled or
polymerized droplet, the unattached strand.
[0140] For protein analysis, proteins can be either trapped within,
or attached to the gel or polymer matrix. If attached, it can be
through a covalent linkage or through an affinity tag, for example
his6 or avi-tag. The proteins can be added to droplets containing
gel or polymer reagent, or they can be formulated along with the
gel or polymerization reagent. Variations that include both are
also possible. The protein can be added to the droplets.
Additionally, it is possible to add DNA to the droplet and allow in
vitro transcription/translation to synthesize the protein.
[0141] The droplets can be kept in liquid form on the microfluidic
device and either gelled or polymerized upon removal, or can be
gelled or polymerized within the droplets anywhere on the device
after the droplets have been formed.
[0142] In an example, multiple plasmids are formulated into a
droplet along with an in vitro transcription/translation reaction.
Genes, encoded by the plasmids, are translated and transcribed to
protein molecules. The protein molecules attach to the polymer via
an avi-tag, the droplets are allowed to gel and the plasmid
molecules become `fixed` or `trapped` within the gel. The gelled
droplets are collected, the emulsion is broken and the solidified
droplets collected and washed. As an example application, DNA is
amplified within a droplet wherein one primer is physically
attached to a polymer monomer. The droplet is then combined with a
droplet containing the enzymes DNA polymerase, luciferase and
sulfurylase. The merged droplets are allowed to gel or polymerize,
they are collected, and if needed, washed. These washed gelled
droplets can then used for a DNA sequencing reaction.
[0143] Surfactants
[0144] The fluids used in the invention may contain one or more
additives, such as agents which reduce surface tensions
(surfactants). Surfactants can include Tween, Span,
fluorosurfactants, and other agents that are soluble in oil
relative to water. In some applications, performance is improved by
adding a second surfactant to the aqueous phase. Surfactants can
aid in controlling or optimizing droplet size, flow and uniformity,
for example by reducing the shear force needed to extrude or inject
droplets into an intersecting channel. This can affect droplet
volume and periodicity, or the rate or frequency at which droplets
break off into an intersecting channel. Furthermore, the surfactant
can serve to stabilize aqueous emulsions in fluorinated oils from
coalescing.
[0145] The droplets may be coated with a surfactant. Preferred
surfactants that may be added to the continuous phase fluid
include, but are not limited to, surfactants such as sorbitan-based
carboxylic acid esters (e.g., the "Span" surfactants, Fluka
Chemika), including sorbitan monolaurate (Span 20), sorbitan
monopalmitate (Span 40), sorbitan monostearate (Span 60) and
sorbitan monooleate (Span 80), and perfluorinated polyethers (e.g.,
DuPont Krytox 157 FSL, FSM, and/or FSH). Other non-limiting
examples of non-ionic surfactants which may be used include
polyoxyethylenated alkylphenols (for example, nonyl-, p-dodecyl-,
and dinonylphenols), polyoxyethylenated straight chain alcohols,
polyoxyethylenated polyoxypropylene glycols, polyoxyethylenated
mercaptans, long chair carboxylic acid esters (for example,
glyceryl and polyglycerl esters of natural fatty acids, propylene
glycol, sorbitol, polyoxyethylenated sorbitol esters,
polyoxyethylene glycol esters, etc.) and alkanolamines (e.g.,
diethanolamine-fatty acid condensates and isopropanolamine-fatty
acid condensates). In addition, ionic surfactants such as sodium
dodecyl sulfate (SDS) may also be used. However, such surfactants
are generally less preferably for many embodiments of the
invention. For instance, in those embodiments where aqueous
droplets are used as nanoreactors for chemical reactions (including
biochemical reactions) or are used to analyze and/or sort
biomaterials, a water soluble surfactant such as SDS may denature
or inactivate the contents of the droplet.
[0146] The carrier fluid can be an oil (e.g., decane, tetradecane
or hexadecane) or fluorocarbon oil that contains a surfactant
(e.g., a non-ionic surfactant such as a Span surfactant) as an
additive (preferably between about 0.2 and 5% by volume, more
preferably about 2%). A user can preferably cause the carrier fluid
to flow through channels of the microfluidic device so that the
surfactant in the carrier fluid coats the channel walls.
[0147] In one embodiment, the fluorosurfactant can be prepared by
reacting the perflourinated polyether DuPont Krytox 157 FSL, FSM,
or FSH with aqueous ammonium hydroxide in a volatile fluorinated
solvent. The solvent and residual water and ammonia can be removed
with a rotary evaporator. The surfactant can then be dissolved
(e.g., 2.5 wt %) in a fluorinated oil (e.g., Flourinert (3M)),
which then serves as the continuous phase of the emulsion.
[0148] Driving Forces
[0149] The invention can use pressure drive flow control, e.g.,
utilizing valves and pumps, to manipulate the flow of cells,
particles, molecules, enzymes or reagents in one or more directions
and/or into one or more channels of a microfluidic device. However,
other methods may also be used, alone or in combination with pumps
and valves, such as electro-osmotic flow control, electrophoresis
and dielectrophoresis (Fulwyer, Science 156, 910 (1974); Li and
Harrison, Analytical Chemistry 69, 1564 (1997); Fiedler, et al.
Analytical Chemistry 70, 1909-1915 (1998); U.S. Pat. No.
5,656,155). Application of these techniques according to the
invention provides more rapid and accurate devices and methods for
analysis or sorting, for example, because the sorting occurs at or
in a sorting module that can be placed at or immediately after a
detection module. This provides a shorter distance for molecules or
cells to travel, they can move more rapidly and with less
turbulence, and can more readily be moved, examined, and sorted in
single file, i.e., one at a time.
[0150] Positive displacement pressure driven flow is a preferred
way of controlling fluid flow and dielectrophoresis is a preferred
way of manipulating droplets within that flow.
[0151] The pressure at the inlet module can also be regulated by
adjusting the pressure on the main and sample inlet channels, for
example, with pressurized syringes feeding into those inlet
channels. By controlling the pressure difference between the oil
and water sources at the inlet module, the size and periodicity of
the droplets generated may be regulated. Alternatively, a valve may
be placed at or coincident to either the inlet module or the sample
inlet channel connected thereto to control the flow of solution
into the inlet module, thereby controlling the size and periodicity
of the droplets. Periodicity and droplet volume may also depend on
channel diameter, the viscosity of the fluids, and shear
pressure.
[0152] Without being bound by any theory, electro-osmosis is
believed to produce motion in a stream containing ions e.g. a
liquid such as a buffer, by application of a voltage differential
or charge gradient between two or more electrodes. Neutral
(uncharged) molecules or cells can be carried by the stream.
Electro-osmosis is particularly suitable for rapidly changing the
course, direction or speed of flow. Electrophoresis is believed to
produce movement of charged objects in a fluid toward one or more
electrodes of opposite charge, and away from one on or more
electrodes of like charge. Where an aqueous phase is combined with
an oil phase, aqueous droplets are encapsulated or separated from
each other by oil. Typically, the oil phase is not an electrical
conductor and may insulate the droplets from the electro-osmotic
field. In this example, electro-osmosis may be used to drive the
flow of droplets if the oil is modified to carry or react to an
electrical field, or if the oil is substituted for another phase
that is immiscible in water but which does not insulate the water
phase from electrical fields.
[0153] Dielectrophoresis is believed to produce movement of
dielectric objects, which have no net charge, but have regions that
are positively or negatively charged in relation to each other.
Alternating, non-homogeneous electric fields in the presence of
droplets and/or particles, such as cells or molecules, cause the
droplets and/or particles to become electrically polarized and thus
to experience dielectrophoretic forces. Depending on the dielectric
polarizability of the particles and the suspending medium,
dielectric particles will move either toward the regions of high
field strength or low field strength. For example, the
polarizability of living cells depends on their composition,
morphology, and phenotype and is highly dependent on the frequency
of the applied electrical field. Thus, cells of different types and
in different physiological states generally possess distinctly
different dielectric properties, which may provide a basis for cell
separation, e.g., by differential dielecrophoretic forces.
Likewise, the polarizability of droplets also depends upon their
size, shape and composition. For example, droplets that contain
salts can be polarized. According to formulas provided in Fiedler,
et al. Analytical Chemistry 70, 1909-1915 (1998), individual
manipulation of sine, droplets requires field differences
(inhomogeneities) with dimensions close to the droplets.
[0154] The term "dielectrophoretic force gradient" means a
dielectrophoretic force is exerted on an object in an electric
field provided that the object has a different dielectric constant
than the surrounding media. This force can either pull the object
into the region of larger field or push it out of the region of
larger field. The force is attractive or repulsive depending
respectively on whether the object or the surrounding media has the
larger dielectric constant.
[0155] Manipulation is also dependent on permittivity (a dielectric
property) of the droplets and/or particles with the suspending
medium. Thus, polymer particles, living cells show
negative--dielectrophoresis at high-field frequencies in water. For
example, dielectrophoretic forces experienced by a latex sphere in
a 0.5 MV/m field (10 V for a 20 micron electrode gap) in water are
predicted to be about 0.2 piconewtons (pN) for a 3.4 micron latex
sphere to 15 pN for a 15 micron latex sphere (Fiedler, et al.
Analytical Chemistry 70, 1909-1915 (1998)). These values are mostly
greater than the hydrodynamic forces experienced by the sphere in a
stream (about 0.3 pN for a 3.4 micron sphere and 1.5 pN for a 15
micron sphere). Therefore, manipulation of individual cells or
particles can be accomplished in a streaming fluid, such as in a
cell sorter device, using dielectrophoresis. Using conventional
semiconductor technologies, electrodes can be microfabricated onto
a substrate to control the force fields in a microfabricated
sorting device of the invention. Dielectrophoresis is particularly
suitable for moving objects that are electrical conductors. The use
of AC current is preferred, to prevent permanent alignment of ions.
Megahertz frequencies are suitable to provide a net alignment,
attractive force, and motion over relatively long distances. See
U.S. Pat. No. 5,454,472.
[0156] Radiation pressure can also be used in the invention to
deflect and move objects, e.g. droplets and particles (molecules,
cells, particles, etc.) contained therein, with focused beams of
light such as lasers. Flow can also be obtained and controlled by
providing a pressure differential or gradient between one or more
channels of a device or in a method of the invention.
[0157] Molecules, cells or particles (or droplets containing
molecules, cells or particles) can be moved by direct mechanical
switching, e.g., with on-off valves or by squeezing the channels.
Pressure control may also be used, for example, by raising or
lowering an output well to change the pressure inside the channels
on the chip. See, e.g., the devices and methods described U.S. Pat.
No. 6,540,895. These methods and devices can further be used in
combination with the methods and devices described in pending U.S.
Patent Application Publication No. 20010029983 and 20050226742.
Different switching and flow control mechanisms can be combined on
one chip or in one device and can work independently or together as
desired.
[0158] Inlet Module
[0159] The microfluidic device of the present invention includes
one or more inlet modules. An "inlet module" is an area of a
microfluidic substrate device that receives molecules, cells, small
molecules or particles for additional coalescence, detection and/or
sorting. The inlet module can contain one or more inlet channels,
wells or reservoirs, openings, and other features which facilitate
the entry of molecules, cells, small molecules or particles into
the substrate. A substrate may contain more than one inlet module
if desired. Different sample inlet channels can communicate with
the main channel at different inlet modules. Alternately, different
sample inlet channels can communication with the main channel at
the same inlet module. The inlet module is in fluid communication
with the main channel. The inlet module generally comprises a
junction between the sample inlet channel and the main channel such
that a solution of a sample (i.e., a fluid containing a sample such
as molecules, cells, small molecules (organic or inorganic) or
particles) is introduced to the main channel and forms a plurality
of droplets. The sample solution can be pressurized. The sample
inlet channel can intersect the main channel such that the sample
solution is introduced into the main channel at an angle
perpendicular to a stream of fluid passing through the main
channel. For example, the sample inlet channel and main channel
intercept at a T-shaped junction; i.e., such that the sample inlet
channel is perpendicular (90 degrees) to the main channel. However,
the sample inlet channel can intercept the main channel at any
angle, and need not introduce the sample fluid to the channel at an
angle that is perpendicular to that flow. The angle between
intersecting channels is in the range of from about 60 to about 120
degrees. Particular exemplary angles are 45, 60, 90, and 120
degrees.
[0160] Embodiments of the invention are also provided in which
there are two or more inlet modules introducing droplets of samples
into the main channel. For example, a first inlet module may
introduce droplets of a first sample into a flow of fluid in the
main channel and a second inlet module may introduce droplets of a
second sample into the flow of fluid in main channel, and so forth.
The second inlet module is preferably downstream from the first
inlet module (e.g., about 30 .mu.m). The fluids introduced into the
two or more different inlet modules can comprise the same fluid or
the same type of fluid (e.g., different aqueous solutions). For
example, droplets of an aqueous solution containing an enzyme are
introduced into the main channel at the first inlet module and
droplets of aqueous solution containing a substrate for the enzyme
are introduced into the main channel at the second inlet module.
Alternatively, the droplets introduced at the different inlet
modules may be droplets of different fluids which may be compatible
or incompatible. For example, the different droplets may be
different aqueous solutions, or droplets introduced at a first
inlet module may be droplets of one fluid (e.g., an aqueous
solution) whereas droplets introduced at a second inlet module may
be another fluid (e.g., alcohol or oil).
[0161] Droplet Interdigitation
[0162] Particular design embodiments of the microfluidic device
described herein allow for a more reproducible and controllable
interdigitation of droplets of specific liquids followed by
pair-wise coalescence of these droplets, described in further
detail herein. The droplet pairs can contain liquids of different
compositions and/or volumes, which would then combine to allow for
a specific reaction to be investigated. The pair of droplets can
come from any of the following: (i) two continuous aqueous streams
and an oil stream; (ii) a continuous aqueous stream, an emulsion
stream, and an oil stream, or (iii) two emulsion streams and an oil
stream. The term "interdigitation" as used herein means pairing of
droplets from separate aqueous streams, or from two separate inlet
nozzles, for eventual coalescence.
[0163] The nozzle designs described herein enhance the
interdigitation of droplets and further improves coalescence of
droplets due to the better control of the interdigitation and
smaller distance between pairs of droplets. The greater control
over interdigitation allows for a perfect control over the
frequency of either of the droplets. To obtain the optimum
operation, the spacing between droplets and coupling of the
droplets can be adjusted by adjusting flow of any of the streams,
viscosity of the streams, nozzle design (including orifice
diameter, the channel angle, and post-orifice neck of the
nozzle
[0164] Reservoir/Well
[0165] A device of the invention can include a sample solution
reservoir or well or other apparatus for introducing a sample to
the device, at the inlet module, which is typically in fluid
communication with inlet channel. Reservoirs and wells used for
loading one or more samples onto the microfluidic device of the
present invention, include but are not limited to, syringes,
cartridges, vials, eppendorf tubes and cell culture materials
(e.g., 96 well plates). A reservoir may facilitate introduction of
molecules or cells into the device and into the sample inlet
channel of each analysis unit.
[0166] Fluidic Interconnects
[0167] The microfluidic device can include a syringe (or other
glass container) that is treated with a vapor or solution of an
appropriate PEG-silane to effect the surface PEG functionalization.
The purpose for treating the walls of glass containers (e.g.,
syringes) with a PEG functionality is to prevent biological
adhesion to the inner walls of the container, which frustrates the
proper transfer of biological/chemical materials into the
microfluidic device of the present invention. The inlet channel is
further connected to a means for introducing a sample to said
device. The means can be a well or reservoir. The means can be
temperature controlled. The inlet module may also contain a
connector adapted to receive a suitable piece of tubing, such as
liquid chromatography or HPLC tubing, through which a sample may be
supplied. Such an arrangement facilitates introducing the sample
solution under positive pressure in order to achieve a desired
infusion rate at the inlet module.
[0168] The interconnections, including tubes, must be extremely
clean and make excellent bonding with the PDMS surface in order to
allow proper operation of the device. The difficulty in making a
fluidic! connection to a microfluidic device is primarily due to
the difficulty in transitioning from a macroscopic fluid line into
the device while minimizing dead volume.
[0169] In order to minimize contamination and leakage and allow for
greater reproducibility and reliability are improved, tubes and
interconnects for the PDMS slab can be cured in place. The tubes
and interconnects can be placed in position by applying a UV-cured
adhesive to allow for holding the tubes in place on the silicone
wafer. Once the tubes are placed in position, PDMS can be poured
over the wafer and cured. The cured PDMS, along with the tubes in
place, can be peeled off of the silicone wafer easily. This process
can be applied to fluidics channels as well as other connection
channels. Once the adhesive is applied onto the wafer, the process
will allow for quick templating of PDMS slabs with exact
reproducibility of channel locations and cleanliness. Tubes of any
size can be implemented for this process. This process allows for
less stress on the interconnection joints and smaller
interconnection footprints in the device (see, for example,
PCT/US2006/02186 filed on Jun. 1, 2006; PCT/US2006/021280 filed on
Jun. 1, 2006 and PCT/US2006/021380 filed on Jun. 1, 2006, each of
which is incorporated by reference in their entirety for all
purposes).
[0170] The tubing side of the interconnect can be mounted into a
retaining block that provides precise registration of the tubing,
while the microfluidic device can be positioned accurately in a
carrier that the retaining block would align and clamp to. The
total dead volume associated with these designs would be critically
dependent on how accurately the two mating surfaces could be
positioned relative to each other. The maximum force required to
maintain the seal would be limited by the exact shape and
composition of the sealing materials as well as the rigidity and
strength of the device itself. The shapes of the mating surfaces
can be tailored to the minimal leakage potential, sealing force
required, and potential for misalignment. By way of non-limiting
example, the single ring indicated in can be replaced with a series
of rings of appropriate cross-sectional shape.
[0171] Reservoirs and wells used for loading one or more samples
onto the microfluidic device of the present invention, include but
are not limited to, syringes, cartridges, vials, eppendorf tubes
and cell culture materials (e.g., 96 well plates) as described
above. One of the issues to be resolved in loading samples into the
inlet channel at the inlet module of the substrate is the size
difference between the loading means or injection means, e.g.,
capillary or HPLC tubing and the inlet channel. It is necessary to
create an interconnect and loading method which limits leaks and
minimizes dead volume and compliance problems. Several devices and
methods described in further detail herein address and solve these
art problems.
[0172] Self-Aligning Fluidic Interconnects
[0173] The present invention includes one or more inlet modules
comprising self-aligning fluidic interconnects proximate to one or
more inlet channels to improve the efficiency of sample loading
and/or injection.
[0174] The present invention proposes the use of small
interconnects based on creating a radial seal instead of a face
seal between the microfluidic device and interconnect. The inserted
interconnect would have a larger diameter than the mating feature
on the device. When inserted, the stretching of the chip would
provide the sealing force needed to make a leak-free seal between
the external fluid lines and the microfluidic device. FIG. 11
details design possibilities for making this seal.
[0175] Studies were performed with the leftmost design of FIG. 1
using a cast hole in PDMS and 1/32'' PEEK tubing, which showed that
the seal was able to withstand more than 90 PSI of pressure without
leakage.
[0176] In order to handle instrument and chip manufacturing
tolerances, the external interconnect must be self aligning and the
"capture radius" of the molded hole must be large enough to
reliably steer the interconnect to the sealing surfaces. FIG. 12
shows that the entrance to the molded hole is large enough to
guarantee capture but tapers down to the sealing surfaces. The
external interconnect could be made directly out of the tubing
leading up to the microfluidic substrate, thus eliminating
potential leak points and unswept volumes. As seen in FIG. 12, the
interconnect is surrounded by the substrate interconnects or "chip
dock" for most of its length to make certain it is held within the
tolerance stack-up of the system. The external interconnect is made
from a hard but flexible material such as 1/32'' PEEK tubing. The
features in the microfluidic device can be molded directly into it
during the manufacturing process, while the inserted seals can be
molded/machined directly onto the tubing ends or molded as
individual pieces and mechanically fastened to the tubing. The
retaining ferrule shown in FIG. 12 would be attached during
manufacturing and provide good absolute referencing of the tube
length. The ferrule could be an off-the-shelf component or a custom
manufactured part and be made from, for example, a polymer, an
elastomer, or a metal. The tubing end could be tapered on the end
(top most diagram) or squared off (the figure above). The specific
shape of the end will be controlled by how easily the microfluidic
device will gall during insertion.
[0177] Alternatively, it is also possible to mold all the
interconnects needed for each tube into a single monolithic
self-aligned part as detailed in FIG. 13. This may help reduce the
difficulty in maintaining alignment of many external fluidic lines
to the chip.
[0178] Methods for Molding Fluidic Interconnects Directly on the
Substrate
[0179] The present invention also provides methods of direct
molding of fluidic interconnects into a microfluidic device.
Development of a commercial microfluidic platform requires a
simple, reliable fluidic interconnect in order to reduce the chance
of operator error and leaks. Molding these interconnects directly
into the microfluidic device requires precise alignment of the
molding pins to 30 the patterned shim (the "master" manufactured
from Silicon/photoresist or made from some metal) used to form the
microfluidic and electrical channels. The extreme tolerances
required when molding with low viscosity elastomer such as PDMS
requires near perfect sealing of the pin face to the mast r, while
still accommodating imperfections in the master and assembly of the
molding tool. In an embodiment, the present invention provides a
precise and repeatable method of molding of interconnects while
accommodating the imperfections in the molding process by
introducing movable pins captured in an elastomeric sleeve molded
directly into the tool. In order to effectively produce at
relatively low volume and be able to inexpensively prototype
devices, the tool must be able to use masters generated using
standard photolithographic processes (e.g. silicon wafers patterned
with SU- 8).
[0180] FIG. 14 shows a schematic of a molding tool based on this
concept. In FIG. 14, the pins (orange) are captured within an
elestomeric molded sleeve. A compression plate made from a rigid
backer plate and foam rubber is used to apply gentle even pressure
to the pins and generate the force needed to make the pins
uniformly contact the master. The molded sleeve was found to be
necessary to consistently prevent the uncured elastomer from
penetrating the region between the pin and the top plate. Early
designs used pins captured in tight clearance holes, and the pins
would frequently bind in place (even with lubricant), preventing
smooth motion of the pins and improper contact with the master.
This would in turn cause a thin film of the elastomer to form
between the bottom of the pin and the master ("Flash"). This flash
prevents proper operation of the interconnects during chip
operation. The addition of the elastomeric sleeves around each pin
eliminated this problem, and produce consistent, reliable shutoff
between the master and the pins.
[0181] Acoustic Actuator
[0182] The well or reservoir of the inlet module further include an
acoustic actuator. To obtain one droplet comprising a single
element of a specific biological/chemical material (e.g., a cell),
separation of biological/chemical material, and uniformity of the
number density of biological/chemical materials in a microfluidic
channel is desirable. Accordingly, the microfluidic device can
include an acoustic actuator. The loaded sample
(biological/chemical material) can be well mixed and separated in a
small chamber by acoustic wave before sending out to the nozzle
region for encapsulation. The frequency of the acoustic wave should
be fine tuned so as not to cause any damage to the cells. The
biological effects of acoustic mixing have been well studied (e.g.,
in the ink-jet industry) and many published literatures also showed
that piezoelectric microfluidic device can deliver intact
biological payloads such as live microorganisms and DNA.
[0183] The design of the acoustic resonant can use a Piezoelectric
bimorph flat plate located on the side of the carved resonant in
the PDMS slab. The resonant inlet can connect to the cell flow
input channel and the outlet can connect to the cell flow pinching
channel. The piezoelectric driving way form can be carefully
optimized to select the critical frequencies that can separate
cells in fluids. There are five parameters to optimize beyond the
frequency parameter and Lab electronics can be used to optimize the
piezoelectric driving waveform. Afterwards, a low cost circuit can
be designed to generate only the optimized waveform in a preferred
microfluidic device.
Coalescence Module
[0184] The microfluidic device of the present invention also
includes one or more coalescence modules. A "coalescence module" is
within or coincident with at least a portion of the main channel at
or downstream of the inlet module where molecules, cells, small
molecules or particles comprised within droplets are brought within
proximity of other droplets comprising molecules, cells, small
molecules or particles and where the droplets in proximity fuse,
coalesce or combine their contents. The coalescence module can also
include an apparatus, for generating an electric force.
[0185] The electric force exerted on the fluidic droplet may be
large enough to cause the droplet to move within the liquid. In
some cases, the electric force exerted on the fluidic droplet may
be used to direct a desired motion of the droplet within the
liquid, for example, to or within a channel or a microfluidic
channel (e.g., as further described herein), etc.
[0186] The electric field can be generated from an electric field
generator, i.e., a device or system able to create an electric
field that can be applied to the fluid. The electric field
generator may produce an AC field (i.e., one that varies
periodically with respect to time, for example, sinusoidally,
sawtooth, square, etc.), a DC field (i.e., one that is constant
with respect to time), a pulsed field, etc. The electric field
generator may be constructed and arranged to create an electric
field within a fluid contained with a channel or a microfluidic
channel. The electric field generator may be integral to or
separate from the fluidic system containing the channel or
microfluidic channel, according to some embodiments. As used
herein, "integral" means that portions of the components integral
to each other are joined in such a way that the components cannot
be in manually separated from each other without cutting or
breaking at least one of the components.
[0187] Techniques for producing a suitable electric field (which
may be AC, DC, etc.) are known to those of ordinary skill in the
art. For example, in one embodiment, an electric field is produced
by applying voltage across a pair of electrodes, which may be
positioned on or embedded within the fluidic system (for example,
within a substrate defining the channel or microfluidic channel),
and/or positioned proximate the fluid such that at least a portion
of the electric field interacts with the fluid. The electrodes can
be fashioned from any suitable electrode material or materials
known to those of ordinary skill in the art, including, but not
limited to, silver, gold, copper, carbon, platinum, copper,
tungstein, tin, cadmium, nickel, indium tin oxide ("ITO"), etc., as
well as combinations thereof.
[0188] Electrodes
[0189] The device can include channels for use in fluid control and
other channels filled with a metal alloy for casting integrated
metal alloy components (i.e., electrodes). Alternatively, the
electrodes can be manufactured using other technologies (e.g.,
lithographically patterned electrodes made from indium tin oxide or
a metal such as platinum). The microfluidic device can include
metal alloy components useful for performing electrical functions
on fluids, including but not limited to, coalescing droplets,
charging droplets, sorting droplets, detecting droplets and shaking
droplets to mix the contents of coalesced droplets. The device can
contain more than one of the above mentioned components for more
than one of the above mentioned functions.
[0190] The electrodes comprising metal alloy components may either
terminate at fluid channels or be isolated from fluid channels. The
electrodes can be constructed by filling the appropriate channels
with metal alloy. One way this can be accomplished is to use
positive pressure injection of the metal alloy in a melted state,
such as with a syringe, into the channels, and then cool the metal
alloy to a solid form. Another example is to use negative pressure
to draw the metal alloy in a melted state into the channels, and
then cool the metal alloy to a solid form. This can be accomplished
for example by use of capillary forces. Another method of
construction can use any of the above mentioned embodiments, and
then flush out the metal alloy in a melted state with another
liquid to define the geometry of the metal alloy components.
Another example is to use any of the above mentioned embodiments,
and then use a localized cold probe to define a solid termination
point for the metal alloy, and then cool the remaining metal alloy
to a solid form. A further example is to use another material, such
as microscopic solder spheres or UV curable conductive ink, to form
a barrier between fluid and metal alloy channels, to define the
geometry of the metal alloy components.
[0191] The device can include a combination of both integrated
metal alloy components and a patterned electrically conductive
layer. The patterned electrically conductive layer can have
features patterned such that their boundaries are within a
leak-proof seal. The device can have a patterned electrically
conductive feature as one of two charging electrodes and one
integrated metal alloy component as the other of two charging
electrodes.
[0192] The device can include a plurality of electrodes that are
insulated from the fluid present in the device, and the method of
operation including appropriate application of dielectrical signals
and appropriate fluids. In known devices, the electrodes are
typically in contact with the fluids in order to allow discharge of
species that would otherwise screen the applied dielectric field.
Whereas, in devices where the electrodes have been insulated from
the fluid, this screening effect typically arises so quickly that
the device is not useful for any significantly extended period of
time. The drawbacks of electrodes in contact with the fluids vs.
insulated electrodes are (a) degraded reliability against leaking
(since the interface between the electrodes and the other
components of the device may be more difficult to effect a
leak-proof seal), and (b) degraded reliability against electrode
corrosion (whose failure mode effects include failure of
application of dielectric fields, and fluid channel
contamination).
[0193] The device of the present invention comprising a plurality
of electrodes that are insulated from the fluid present in the
device counteracts this screening effect by extending the screening
rise time and including a polarity switch for all of the different
dielectric fields applied in the device. The screening rise time is
extended by using fluids with dielectrical properties. A polarity
switch for all of the different dielectric fields applied in the
device is achieved by using an algorithm for dielectrical control,
which switches the polarity of the dielectrical fields at a
frequency sufficiently high to maintain proper dielectrical
function of the device. This dielectrical control algorithm may
also switch the polarity for the dielectric fields in a cascading,
time controlled manner starting at the fluid origin point and
progressing downstream, so that given fluid components experience
one polarity at every point along their course. The device of the
present invention can be used with metal alloy electrodes or using
a combination of metal alloy electrodes and patterned conductive
film electrodes.
[0194] The invention can provide a microfluidic device using
injected electrodes. The interface between the microscopic
electrode (typically 25 .mu.m thick) and the macroscopic
interconnect can easily fail if the joint between the two is
flexed. The flexing of the joint can be eliminated by securing a
firm material that serves to fasten, support, and re-enforce the
joint (i.e., a grommet) into the interface. In order to prevent
flexing, the mating surface of the device can be manufactured from
a hard material such as glass or plastic. The electrical connection
with the external system can be made by securing the device such
that it connects to a spring loaded contact, which is either offset
from the grommet (thereby minimizing the force applied to the
solder region), or centered on the grommet (as long as the contact
does not touch the solder).
[0195] The metal alloy components are also useful for performing
optical functions on fluids, including but not limited to, optical
detection of droplets in a geometry which may include a mirror.
[0196] To prevent leakage of fluid out of electrodes placed within
microfluidic channels, the microfluidic device can include a layer
patterned with channels for fluid control, and another layer with
patterned electrically conductive features, where the features are
patterned such that their boundaries are within a leak-proof seal.
The leak-proof seal can be achieved at the interface between the
unpatterned areas of the fluid control layer and the unpatterned
areas of the electrically conductive layer. The leak-proof seal can
also be achieved by a third interfacial layer between the fluid
control layer and the unpatterned areas of the electrically
conductive layer. The third interfacial layer can or can not be
perforated at specific locations to allow contact between the fluid
and the electrically conductive layer. Electrical access ports can
also be patterned in the fluid control layer.
[0197] The electrodes and patterned electrically conductive layers
as described can be associated with any module of the device (inlet
module, coalescence module, mixing module, delay module, detection
module and sorting module) to generate dielectric or electric
forces to manipulate and control the droplets and their
contents.
[0198] Effective control of uncharged droplets within microfluidic
devices can require the generation of extremely strong dielectric
field gradients. The fringe fields from the edges of a parallel
plate capacitator can provide an excellent topology to form these
gradients. The microfluidic device according to the present
invention can include placing a fluidic channel between two
parallel electrodes, which can result in a steep electric field
gradient at the entrance to the electrodes due to edge effects at
the ends of the electrode pair. Placing these pairs of electrodes
at a symmetric channel split can allow precise bi-directional
control of droplet within a device. Using the same principle, only
with asymmetric splits, can allow single ended control of the
droplet direction in the same manner. Alternatively, a variation on
this geometry will allow precise control of the droplet phase by
shifting.
[0199] In some cases, transparent or substantially transparent
electrodes can be used. The electric field generator can be
constructed and arranged (e.g., positioned) to create an electric
field applicable to the fluid of at least about 0.01 V/micrometer,
and, in some cases, at least about 0.03 V/micrometer, at least
about 0.05 V/micrometer, at least about 0.08 V/micrometer, at least
about 0.1 V/micrometer, at least about 0.3 V/micrometer, at least
about 0.5 V/micrometer, at least about 0.7 V/micrometer, at least
about 1 V/micrometer, at least about 1.2 V/micrometer, at least
about 1.4 V/micrometer, at least about 1.6 V/micrometer, or at
least about 2 V/micrometer. In some embodiments, even higher
electric field intensities may be used, for example, at least about
2 V/micrometer, at least about 3 V/micrometer, at least about 5
V/micrometer, at least about 7 V/micrometer, or at least about 10
V/micrometer or more.
[0200] As described, an electric field may be applied to fluidic
droplets to cause the droplets to experience an electric force. The
electric force exerted on the fluidic droplets may be, in some
cases, at least about 10.sup.-16 N/micrometer.sup.3. In certain
cases, the electric force exerted on the fluidic droplets may be
greater, e.g., at least about 10.sup.-15 N/micrometer.sup.3, at
least about 10.sup.-14 N/micrometer.sup.3, at least about
10.sup.-13 N/micrometer.sup.3, at least about 10.sup.-12
N/micrometer.sup.3, at least about 10.sup.-11 N/micrometer.sup.3,
at least about 10.sup.-10 N/micrometer3, at least about 10.sup.-9
N/micrometer.sup.3, at least about 10.sup.-8 N/micrometer.sup.3, or
at least about 10.sup.-7 N/micrometer.sup.3 or more. The electric
force exerted on the fluidic droplets, relative to the surface area
of the fluid, may be at least about 10.sup.-15 N/micrometer.sup.2,
and in some cases, at least about 10.sup.-14 N/micrometer.sup.2, at
least about 10.sup.-13 N/micrometer.sup.2, at least about
10.sup.-12 N/micrometer.sup.2, at least about 10.sup.-11
N/micrometer.sup.2, at least about 10.sup.-10 N/micrometer.sup.2,
at least about 10.sup.-9 N/micrometer.sup.2, at least about
10.sup.-8 N/micrometer.sup.2, at least about 10.sup.-7
N/micrometer.sup.2, or at least about 10.sup.-6 N/micrometer.sup.2
or more. In yet other embodiments, the electric force exerted on
the fluidic droplets may be at least about 10.sup.-9 N, at least
about 10.sup.-8 N, at least about 10.sup.-7 N, at least about
10.sup.-6 N, at least about 10.sup.-5 N, or at least about
10.sup.-4 N or more in some cases.
[0201] Channel Expansion Geometries
[0202] In preferred embodiments described herein, droplet
coalescence is presently carried out by having two droplet forming
nozzles emitting droplets into the same main channel. The size of
the nozzles allow for one nozzle to form a large drop that fills
the exhaust line while the other nozzle forms a drop that is
smaller than the first. The smaller droplet is formed at a rate
that is less than the larger droplet rate, which insures that at
most one small droplet is between big droplets. Normally, the small
droplet will catch up to the larger one over a relatively short
distance, but sometimes the recirculation zone behind the large
drop causes the small drop to separate from the large drop
cyclically. In addition, the small drop occasionally does not catch
up with the large one over the distance between the nozzles and the
coalescing electrodes. Thus, in some situations is a need for a
more robust coalescence scheme.
[0203] Geometric alterations in the coalescence module can create a
more robust, reliable coalescence or fusing of droplets over a
wider range of sizes and flows. The solution to improve the
performance is to place an expansion in the main channel between
the electrodes. FIG. 15 is a schematic diagram of the improved
coalescence module. Optionally, a small constriction (neckdown)
just before this expansion can be used to better align the droplets
on their way into the coalescence point (also shown in the FIG.
15). This optional neckdown can help center the small droplet in
the channel stream lines, reducing the chance that it will flow
around the larger droplet prior to coalescing in the expansion. The
electrode pair may be placed on either one side of the channel or
on both sides.
[0204] The expansion in the coalescing region allows for a dramatic
catching up of the small drop to the large drop, as shown through
micrographs taken on an operating device. The volume of the
expansion is big enough to slow the large droplet down so that the
small drop always catches up to the large drop, but doesn't allow
the next large drop to catch up and make contact with the pair to
be coalesced. The electrodes allow for coalescence to take place
when the drops are in contact with each other and passing through
the field gradient.
Detection Module
[0205] The microfluidic device of the present invention can also
include one or more detection modules. A "detection module" is a
location within the device, typically within the main channel where
molecules, cells, small molecules or particles are to be detected,
identified, measured or interrogated on the basis of at least one
predetermined characteristic. The molecules, cells, small molecules
or particles can be examined one at a time, and the characteristic
is detected or measured optically, for example, by testing for the
presence or amount of a reporter. For example, the detection module
is in communication with one or more detection apparatuses. The
detection apparatuses can be optical or electrical detectors or
combinations thereof. Examples of suitable detection apparatuses
include optical waveguides, microscopes, diodes, light stimulating
devices, (e.g., lasers), photo multiplier tubes, and processors
(e.g., computers and software), and combinations thereof, which
cooperate to detect a signal representative of a characteristic,
marker, or reporter, and to determine and direct the measurement or
the sorting action at the sorting module. However, other detection
techniques can also be employed
[0206] The term "determining," as used herein, generally refers to
the analysis or measurement of a species, for example,
quantitatively or qualitatively, and/or the detection of the
presence or absence of species. "Determining" may also refer to the
analysis or measurement of an interaction between more species, for
example, quantitatively or qualitatively, or by detecting the
presence or absence of the interaction. Examples of suitable
techniques include, but are not limited to, spectroscopy such as
infrared, absorption, fluorescence, UV/visible, FTIR ("Fourier
Transform Infrared Spectroscopy"), or Raman; gravimetric
techniques; ellipsometry; piezoelectric measurements; immunoassays;
electrochemical measurements; optical measurements such as optical
density measurements; circular dichroism; light scattering
measurements such as quasielectric light scattering; polarimetry;
refractometry; or turbidity measurements as described further
herein.
[0207] A detection module is within, communicating or coincident
with a portion of the main channel at or downstream of the inlet
module and, in sorting embodiments, at, proximate to, or upstream
of, the sorting module or branch point. The sorting module may be
located immediately downstream of the detection module or it may be
separated by a suitable distance consistent with the size of the
molecules, the channel dimensions and the detection system. Precise
boundaries for the detection module are not required, but are
preferred.
[0208] Detection modules used for detecting molecules and cells
have a cross-sectional area large enough to allow a desired
molecule, cells, bead, or particles to pass through without being
substantially slowed down relative to the flow carrying it. The
dimensions of the detection module are influenced by the nature of
the sample under study and, in particular, by the size of the
droplets, beads. particles, molecules or cells (including virions)
under study. For example, mammalian cells can have a diameter of
about 1 to 50 microns, more typically 10 to 30 microns, although
some mammalian cells (e.g., fat cells) can be larger than 120
microns. Plant cells are generally 10 to 100 microns. However,
other molecules or particles can be smaller with a diameter from
about 20 nm to about 500 nm.
[0209] Waveguides
[0210] The present invention provides self-aligning optical
waveguides and optical elements (lenses, mirrors, interconnects,
etc.) for detection and control of droplets. Such waveguides can be
provide well defined optical access to the fluidic channels to
permit optical scattering, absorption, fluorescence, or any other
optical measurement technique.
[0211] In order to create the waveguides, a separate series of
channels and useful shapes (lenses, mirrors, etc) can be created
either simultaneously within the other channels in the substrate
(i.e. in the same processing step) or in successive steps. The
reusable master created in this way can then used to form the
waveguide components and fluid channels without the need for
special fixturing or careful shipment in subsequent steps. The
extra channels or shapes can then filled with a high index of
refraction liquid (for waveguides) or reflective material (for
mirrors) through injection into the channel or void. The liquid can
either remain as a fluid or be allowed to solidify. UV cure epoxies
used by the telecommunications industry are excellent choices for
the waveguide materials. Possible waveguide geometry can include a
focusing lens and a back-reflecting mirror.
[0212] Sensors
[0213] One or more detections sensors and/or processors may be
positioned to be in sensing communication with the fluidic droplet.
"Sensing communication," as used herein, means that the sensor may
be positioned anywhere such that the fluidic droplet within the
fluidic system (e.g., within a channel), and/or a portion of the
fluidic system containing the fluidic droplet may be sensed and/or
determined in some fashion. For example, the sensor may be in
sensing communication with the fluidic droplet and/or the portion
of the fluidic system containing the fluidic droplet fluidly,
optically or visually, thermally, pneumatically, electronically, or
the like. The sensor can be positioned proximate the fluidic
system, for example, embedded within or integrally connected to a
wall of a channel, or positioned separately from the fluidic system
but with physical, electrical, and/or optical communication with
the fluidic system so as to be able to sense and/or determine the
fluidic droplet and/or a portion of the fluidic system containing
the fluidic droplet (e.g., a channel or a microchannel, a liquid
containing the fluidic droplet, etc.). For example, a sensor may be
free of any physical connection with a channel containing a
droplet, but may be positioned so as to detect electromagnetic
radiation arising from the droplet or the fluidic system, such as
infrared, ultraviolet, or visible light. The electromagnetic
radiation may be produced by the droplet, and/or may arise from
other portions of the fluidic system (or externally of the fluidic
system) and interact with the fluidic droplet and/or the portion of
the fluidic system containing the fluidic droplet in such as a
manner as to indicate one or more characteristics of the fluidic
droplet, for example, through absorption, reflection, diffraction,
refraction, fluorescence, phosphorescence, changes in polarity,
phase changes, changes with respect to time, etc. As an example, a
laser may be directed towards the fluidic droplet and/or the liquid
surrounding the fluidic droplet, and the fluorescence of the
fluidic droplet and/or the surrounding liquid may be determined.
"Sensing communication," as used herein may also be direct or
indirect. As an example, light from the fluidic droplet may be
directed to a sensor, or directed first through a fiber optic
system, a waveguide, etc., before being directed to a sensor.
[0214] Non-limiting examples of detection sensors useful in the
invention include optical or electromagnetically-based systems. For
example, the sensor may be a fluorescence sensor (e.g., stimulated
by a laser), a microscopy system (which may include a camera or
other recording device), or the like. As another example, the
sensor may be an electronic sensor, e.g., a sensor able to
determine an electric field or other electrical characteristic. For
example, the sensor may detect capacitance, inductance, etc., of a
fluidic droplet and/or the portion of the fluidic system containing
the fluidic droplet. In some cases, the sensor may be connected to
a processor, which in turn, cause an operation to be performed on
the fluidic droplet, for example, by sorting the droplet.
[0215] Characteristics
[0216] Characteristics determinable with respect to the droplet and
usable in the invention can be identified by those of ordinary
skill in the art. Non-limiting examples of such characteristics
include fluorescence, spectroscopy (e.g., optical, infrared,
ultraviolet, etc.), radioactivity, mass, volume, density,
temperature, viscosity, pH, concentration of a substance, such as a
biological substance (e.g., a protein, a nucleic acid, etc.), or
the like.
[0217] A corresponding signal is then produced, for example
indicating that "yes" the characteristic is present, or "no" it is
not. The signal may correspond to a characteristic qualitatively or
quantitatively. That is, the amount of the signal can be measured
and can correspond to the degree to which a characteristic is
present. For example, the strength of the signal may indicate the
size of a molecule, or the potency or amount of an enzyme expressed
by a cell, or a positive or negative reaction such as binding or
hybridization of one molecule to another, or a chemical reaction of
a substrate catalyzed by an enzyme. In response to the signal, data
can be collected and/or a control system in the sorting module, if
present, can be activated to divert a droplet into one branch
channel or another for delivery to the collection module or waste
module. Thus, in sorting embodiments, molecules or cells within a
droplet at a sorting module can be sorted into an appropriate
branch channel according to a signal produced by the corresponding
examination at a detection module. The means of changing the flow
path can be accomplished through mechanical, electrical, optical,
or some other technique as described herein.
[0218] A preferred detector is an optical detector, such as a
microscope, which may be coupled with a computer and/or other image
processing or enhancement devices to process images or information
produced by the microscope using known techniques. For example,
molecules can be analyzed and/or sorted by size or molecular
weight. Enzymes can be analyzed and/or sorted by the extent to
which they catalyze chemical reaction of a substrate (conversely,
substrate can be analyzed and/or sorted by the level of chemical
reactivity catalyzed by an enzyme). Cells can be sorted according
to whether they contain or produce a particular protein, by using
an optical detector to examine each cell for an optic indication of
the presence or amount of that protein. The protein may itself be
detectable, for example by a characteristic fluorescence, or it may
be labeled or associated with a reporter that produces a detectable
signal when the desired protein is present, or is present in at
least a threshold amount. There is no limit to the kind or number
of characteristics that can be identified or measured using the
techniques of the invention, which include without limitation
surface characteristics of the cell and intracellular
characteristics, provided only that the characteristic or
characteristics of interest for sorting can be sufficiently
identified and detected or measured to distinguish cells having the
desired characteristic(s) from those which do not. For example, any
label or reporter as described herein can be used as the basis for
analyzing and/or sorting molecules or cells, i.e. detecting
molecules or cells to be collected.
[0219] Fluorescence Polarization
[0220] As described herein, the biological/chemical entity to be
analyzed may itself be detectable, for example by a characteristic
fluorescence, or it may be labeled or associated with a reporter
that produces a detectable signal when the desired protein is
present, or is present in at least a threshold amount.
[0221] Luminescent colloidal semiconductor nanocrystals called
quantum dots or q-dots (QD) are inorganic fluorophores that have
the potential to circumvent some of the functional limitations
encountered by organic dyes. In particular, CdSe--ZnS core-shell
QDs exhibit size-dependent tunable photoluminescence (PL) with
narrow emission bandwidths (FWHM .about.30 to 45 nm) that span the
visible spectrum and broad absorption bands. These allow
simultaneous excitation of several particle sizes (colors) at a
common wavelength. This, in turn, allows simultaneous resolution of
several colors using standard instrumentation. CdSe--ZnS QDs also
have high quantum yields, are resistant to photodegradation, and
can be detected optically at concentrations comparable to organic
dyes.
[0222] Quantum dots are nano-scale semiconductors typically
consisting of materials such as crystalline cadmium selenide. The
term `q-dot` emphasizes the quantum confinement effect of these
materials, and typically refers to fluorescent nanocrystals in the
quantum confined size range. Quantum confinement refers to the
light emission from bulk (macroscopic) semiconductors such as LEDs
which results from exciting the semiconductor either electrically
or by shining light on it, creating electron-hole pairs which, when
they recombine, emit light. The energy, and therefore the
wavelength, of the emitted light is governed by the composition of
the semiconductor material. If, however, the physical size of the
semiconductor is considerably reduced to be much smaller than the
natural radius of the electron-hole pair (Bohr radius), additional
energy is required to "confine" this excitation within the
nanoscopic semiconductor structure leading to a shift in the
emission to shorter wavelengths. Three different q-dots in several
concentrations each can be placed in a microdroplet, and can then
be used with a microfluidic device to decode what is in the drop.
The Q-dot readout extension to the fluorescence station can be
incorporated into the design of the microfluidic device. A series
of dichroic beamsplitters, emission filters, and detectors can be
stacked onto the system, allowing measurement of the required five
emission channels (two fluorescence polarization signals and three
q-dot bands).
[0223] Fluorescence Polarization (FP) detection technology enables
homogeneous assays suitable for high throughput screening assays in
the Drug Discovery field. The most common label in the assays is
fluorescein. In FP-assay the fluorophore is excited with polarized
light. Only fluorophores parallel to the light absorb and are
excited. The excited state has a lifetime before the light emission
occurs. this time the labeled fluorophore molecule rotates and the
polarization of the light emitted differs from the excitation
plane. To evaluate the polarization two measurements are needed:
the first using a polarized emission filter parallel to the
excitation filter (S-plane) and the second with a polarized
emission filter perpendicular to the excitation filter (P-plane).
The Fluorescence Polarization response is given as mP
(milli-Polarization level) and is obtained from the equation:
Polarization (mP)=1000*(S-G*P)/(S+G*P)
[0224] Where S and P are background subtracted fluorescence count
rates and G (grating) is an instrument and assay dependent
factor.
[0225] The rotational speed of a molecule is dependent on the size
of the molecule, temperature and viscosity of the solution.
Fluorescein has a fluorescence lifetime suitable for the rotation
speeds of molecules in bio-affinity assays like receptor-ligand
binding assays or immunoassays of haptens. The basic principle is
that the labeled compound is small and rotates rapidly (low
polarization). When the labeled compound binds to the larger
molecule, its rotation slows down considerably (polarization
changes from low to high polarization). Thus, FP provides a direct
readout of the extent of tracer binding to protein, nucleic acids,
and other biopolymers.
[0226] Fluorescence polarization technology has been used in basic
research and commercial diagnostic assays for many decades, but has
begun to be widely used in drug discovery only in the past six
years. Originally, FP assays for drug discovery were developed for
single-tube analytical instruments, but the technology was rapidly
converted to high-throughput screening assays when commercial plate
readers with equivalent sensitivity became available. These assays
include such well-known pharmaceutical targets such as kinases,
phosphatases, proteases, G-protein coupled receptors, and nuclear
receptors. Other homogeneous technologies based on fluorescence
intensity have been developed. These include energy transfer,
quenching, and enhancement assays. FP offers several advantages
over these. The assays are usually easier to construct, since the
tracers do not have to respond to binding by intensity changes. In
addition, only one tracer is required and crude receptor
preparations may be utilized. Furthermore, since FP is independent
of intensity, it is relatively immune to colored solutions and
cloudy suspensions. FP offers several advantages in the area of
instrumentation. Because FP is a fundamental property of the
molecule, and the reagents are stable, little or no standardization
is required. FP is relatively insensitive to drift in detector gain
settings and laser power.
[0227] The dyes chosen for FP are commonly used in most cell- and
enzyme-based assays and are designated not to overlap significantly
with the q-dots. The dyes are evaluated both independently and
together with the q-dots (at first off-instrument) to assess the
cross-talk. Preferably, the liquid q-dot labels are read outside a
spectral wavelength band currently used in FACS analysis and
sorting (i.e., the dyes flourescein, Cy3, Cy5, etc). This permits
the use of currently-available assays (dependent on these dyes).
Using specific q-dots, crosstalk is minimized.
[0228] Accordingly, the present invention provides methods to label
droplets and/or nanoreactors formed on a microfluidic device by
using only a single dye code to avoid cross-talk with other dyes
during FP. Additionally, the present invention provides methods to
create FP dye codes to label compounds contained within liquids
(including droplets and/or nanoreactors) where the compound is
designed to be differentiated by FP on a microfluidic device. In
this manner, dye codes having the same color, absorption, and
emission could be used to label compounds within liquids.
[0229] In one aspect, the present invention is directed to the use
of fluorescence polarization to label liquids. Droplets can be
labeled using several means. These labeling means include, but are
not limited to, the use of different dyes, quantum dots,
capacitance, opacity, light scattering, fluorescence intensity
(FI), fluorescence lifetime (FL), fluorescence polarization (FP),
circular dichroism (CD), fluorescence correlation and combinations
of all of these previous labeling means. The following disclosure
describes the use of FP and FI as a means to label droplets on a
microfluidic device. In addition, the use of FL as a means to
adjust the overall FP of a solution, and by varying the
concentration of the total FI, to create a 2-dimensional encoding
scheme is demonstrated.
[0230] In general, molecules that take up more volume will tumble
slower than a smaller molecule coupled to the same fluorophore (see
FIG. 16). FP is independent of the concentration of the dye;
liquids can have vastly different concentrations of FITC in them
yet still have identical FP measurements.
[0231] In a preferred embodiment, a FP dye is an organic dye that
does not interfere with the assay dye is used. Furthermore, since
the total intensity of the FP dye can be quantified, a second
dimension in which to label the droplet is provided. Thus, one can
exploit the differences in FP to create an encoding scheme of dye
within a liquid solution, including droplets. An example is shown
in FIG. 17 whereby the droplets are labeled with 3
differently-sized FITC molecules (i.e., three different droplets
contain FITC molecules and FITC coupled to either biotin or
streptavidin, respectively). Therefore, in a single dimension, FP
can be used to create an encoding scheme. However, the present
invention can also use Fluorescence Intensity (FI) of the overall
solution to create even more labels in a second dimension. An
example of labeling droplets in 2 dimensions is shown in FIG.
18.
[0232] Interestingly, the differences of the fluorescence lifetime
(FL) of two dyes with spectral overlap in the detected emission
wavelength to change the overall FP of the combined solution can
also be exploited (see FIGS. 18 and 19).
[0233] Although FIG. 17 discusses the use of multiple compounds to
which a dye molecule is attached to span a range of FP, it is also
possible to span the range using a high and low molecular weight
compound set. As exemplified by FIG. 19, a dye can be attached to a
large compound (for example streptavidin) and kept at a fixed
concentration, to which a smaller compound (for example, a free dye
molecule) would be titrated into the same solution. The FP of the
solution can be adjusted to be in discernable increments from the
value of the large molecule to somewhere slightly greater than the
FP of the smaller molecule. The [total] dye intensity can be varied
by varying the concentration of the mixture of the two dye-attached
compounds. By varying total dye concentration and the FP, two
dimensions can be used to generate the FP dye codes (FPcodes).
Accordingly, many FPcodes can be generated using only two
compounds.
[0234] This could also include use of large fluorescent proteins
such as GFP and the phycobiliproteins combined with a smaller
molecule.
[0235] Examples of dyes commonly used in biological dyes are listed
in the table below.
TABLE-US-00001 Excitation Emission Examples of Wavelength
Wavelength Compatible Dyes 450 500 Cyan 500 483 533 SYBR Green, FAM
523 568 HEX, VIC 558 610 RED 610 615 640 RED 640 650 670 CY5
[0236] In another aspect, the present invention is directed
labeling solids using properties other than dye emission and dye
concentration. In one embodiment the solid can include, for
example, a bead or location on a solid support or chip. As
demonstrated above for liquids, FI and FL can be two of many
dimensions of characteristics used as labels. By way of
non-limiting example, it is possible to use two dyes with different
FL to change the overall FP for a solid such as a bead or other
mobile solid support.
[0237] In another embodiment, a linker can be used to couple the
dye to the bead. The linker can be varied so as to allow the dye to
have differing degrees of freedom in which to rotate (i.e.,
tumble). Varying the linker in this manner can change the FP of the
attached dye, which in unique combinations can be used as a label.
In some embodiments, the beads can be swollen in organic solvent
and the dyes held in place by hydrophobic forces. In this case, the
FP, FI, FL methods described above for liquid labeling can also be
used as a means for labeling the beads. A quenching molecule can
also be used to change the characteristics of a dye. Such quenching
can be continuous or brought about through the interaction of a
molecule, such as a peptide or nucleic acid linker, with differing
means of bringing molecules together depending on the strength of
linker-internal interaction (e.g., a nucleotide stem loop structure
of varying lengths).
[0238] The reactions analyzed on the virtual, random and non-random
arrays (discussed briefly below) can be also increased beyond the
two (cy3 and cy5 intensities) commonly used for multiplexing. For
example, different FP, FI, etc can be used as a read-out.
[0239] Random array decoding: Beads of the prior art use one or
more pre-attached oligonucleotide-coupled beads that are held in
place in a fiber-optic faceplate (for example, those used by
Illumina). The oligos on the beads are decoded using sequential
hybridization of a labeled complementary oligo. The assay of the
prior art uses a separate oligonucleotide complementary zipcode
(`Illumacode`) attached to each type of bead.
[0240] The invention described herein is superior to the methods of
the prior art in that the FP, FI, FL-labeled bead or mobile solid
support can be placed into a random array (e.g., a chip as
manufactured by Illumina) and the FP, FI, FL used to decode the
bead. The FP, FI, FL of the bead can be decoded before using the
chip and the different beads `mapped` as to their specific
locations. Alternatively, the bead can be decoded during attachment
of the assay read-out. Significantly, the methods described by the
present invention can be used to pre-determine the location of each
bead-type either before, or during analysis.
[0241] Virtual array decoding: Methods of the prior art use 2
lasers and 3 detectors to differentiate a set of 100 bead-types.
The beads-types are differentiated by the FI of two different dyes
Present in 1 of 10 concentrations (per dye) contained within the
bead, and the assay detector is used to measure fluorescein
concentration on the bead. The dyes, which are added to
organic-solvent swollen beads, are not directly attached to the
beads, but remain held within the bead by hydrophobic forces.
[0242] Using the methods of the present invention as described
herein, a second detector to the machines of the prior art used to
measure FP can be added, thereby adding a third dimension and
extending the encoding scheme beyond the 100 available in the prior
art.
[0243] Non-random array decoding: In chips of the prior art (such
as those used by Affymetrix) oligonucleotides are synthesized
directly on the chip. Decoding is simply a matter of knowing the
location of the assay on the chip.
[0244] The methods as described herein can be advantageously used
in conjunction with such chips to increase the number of things
that can be simultaneously analyzed (i.e., multiplexed) on the
chip. By way of non-limiting example, Cy3, Cy5, FL and FP can be
used as analysis markers for hybridization reactions.
[0245] The present invention also provides methods for labeling
micro or nano-sized droplets using Radio Frequency Identification
(RFID). RFID tags can improve the identification of the contents
within the droplets. Preferably, the droplets are utilized within a
microfluidic device.
[0246] RFID is an automatic identification method, relying on
storing and remotely retrieving data using devices called RFID tags
or transponders. An RFID tag is an object that can be attached to
or incorporated into a product, animal, or person for the purpose
of identification using radio waves. Chip-based RFID tags contain
silicon chips and antennae. Passive tags require no internal power
source, whereas active tags require a power source. Hitachi has
"powder" 0.05 mm.times.0.05 mm RFID chips. The new chips are 64
times smaller than the previous record holder, the 0.4 mm.times.0.4
mm mu-chips, and nine times smaller than Hitachi's last year
prototype, and have room for a 128-bit ROM that can store a unique
38-digit ID number.
[0247] In one embodiment, a solution containing RFID tags are
emulsified into droplets and are used as a label for the
identification of the material within the droplet solution.
Applications include, but are not limited to; genetics, genomics,
proteomics, chemical synthesis, biofuels, and others.
[0248] Lasers
[0249] To detect a reporter or determine whether a molecule, cell
or particle has a desired characteristic, the detection module may
include an apparatus for stimulating a reporter for that
characteristic to emit measurable light energy, e.g., a light
source such as a laser, laser diode, light emitting diode (LED),
high-intensity lamp, (e.g., mercury lamp), and the like. Where a
lamp is used, the channels are preferably shielded from light in
all regions except the detection module. Where a laser is used, the
laser can be set to scan across a set of detection modules from
different analysis units. In addition, laser diodes or LED's may be
microfabricated into the same chip that contains the analysis
units. Alternatively, laser diodes or LED's may be incorporated
into a second chip (i.e., a laser diode chip) that is placed
adjacent to the analysis or microchip such that the laser light
from the diodes shines on the detection module(s).
[0250] An integrated semiconductor laser and/or an integrated
photodiode detector can be included on the substrate in the
vicinity of the detection module. This design provides the
advantages of compactness and a shorter optical path for exciting
and/or emitted radiation, thus minimizing distortion and
losses.
[0251] Fluorescence produced by a reporter is excited using a laser
beam focused on molecules (e.g., DNA, protein, enzyme or substrate)
or cells passing through a detection region. Fluorescent reporters
can include, but are not limited to, rhodamine, fluorescein, Texas
red, Cy 3, Cy 5, phycobiliprotein (e.g., phycoerythrin), green
fluorescent protein (GFP), YOYO-1 and PicoGreen. In molecular
fingerprinting applications, the reporter labels can be
fluorescently labeled single nucleotides, such as fluorescein-dNTP,
rhodamine-dNTP, Cy3-dNTP, etc.; where dNTP represents dATP, dTTP,
dUTP or dCTP. The reporter can also be chemically-modified single
nucleotides, such as biotin-dNTP. The reporter can be fluorescently
or chemically labeled amino acids or antibodies (which bind to a
particular antigen, or fragment thereof, when expressed or
displayed by a cell or virus).
[0252] The device can analyze and/or sort cells based on the level
of expression of selected cell markers, such as cell surface
markers, which have a detectable reporter bound thereto, in a
manner similar to that currently employed using
fluorescence-activated cell sorting (FACS) machines. Proteins or
other characteristics within a cell, and which do not necessarily
appear on the cell surface, can also be identified and used as a
basis for sorting. The device can also determine the size or
molecular weight of molecules such as polynucleotides or
polypeptides (including enzymes and other proteins) or fragments
thereof passing through the detection module. Alternatively, the
device can determine the presence or degree of some other
characteristic indicated by a reporter. If desired, the cells,
particles or molecules can be sorted based on this analysis. The
sorted cells, particles or molecules can be collected from the
outlet channels in collection modules (or discarded in wasted
modules) and used as needed. The collected cells, particles or
molecules can be removed from the device or reintroduced to the
device for additional coalescence, analysis and sorting.
[0253] Processors
[0254] As used herein, a "processor" or a "microprocessor" is any
component or device able to receive a signal from one or more
sensors, store the signal, and/or direct one or more responses
(e.g., as described above), for example, by using a mathematical
formula or an electronic or computational circuit. The signal may
be any suitable signal indicative of the environmental factor
determined by the sensor, for example a pneumatic signal, an
electronic signal, an optical signal, a mechanical signal, etc.
[0255] The device of the present invention can comprise features,
such as integrated metal alloy components and/or features patterned
in an electrically conductive layer, for detecting droplets by
broadcasting a signal around a droplet and picking up an electrical
signal in proximity to the droplet.
[0256] Parallel Analysis
[0257] The droplet content detection can also be achieved by
simultaneous detection of contents of multiple droplets in parallel
using spectroscopic fluorescence imaging with sensitivity as high
as single-molecule limit. One can spatially distribute droplets
containing fluorescent entities such as fluorophore biological
markers and/or quantum dots in a two-dimensional sheet in a
microscopic field-of-view. The filed-of-view of those droplets can
then be illuminated by a fluorescence excitation source and the
resulting fluorescence can be spectroscopically imaged. Therefore,
for a given fluorescence detection sensitivity, the throughput of
fluorescence detection compared to a single-drop fluorescence
detection method can be increased by a factor of a/b for a given
sensitivity, where a is the number of droplets that can be imaged
within a given field-of-view, and b is the ratio of the
fluorescence sensitivity of a single-drop fluorescence detector
compared to that of the multiple drop fluorescence detector.
Furthermore, unlike single-drop fluorescent detection method where
the drops are flowed through a detection volume so that their
residence time in the detection volume, and hence the signal
integration time and sensitivity, is limited, the residence time of
the droplet in the field-of-view can be unlimited, thereby allowing
sensitivity as high as the single-molecule limit.
[0258] Beads
[0259] The device of the present invention also comprises the use
of beads and methods for analyzing and sorting beads (i.e., bead
reader device). The device can read and either sort or not sort
droplets containing one or more of a set of two or more beads. Each
bead can be differentiated from each other bead within a set. Beads
can be separated by several tags including, but not limited to,
quantum dyes, fluorescent dyes, ratios of fluorescent dyes,
radioactivity, radio-tags, etc. For example, a set of beads
containing a ratio of two dyes in discrete amounts with an
apparatus for detecting and differentiating beads containing one
discrete ratio from the other beads in this set having a different
ratio of the two dyes. The microfluidic device can include
paramagnetic beads. The paramagnetic beads can introduce and remove
chemical components from droplets using droplet coalescence and
breakup events. The paramagnetic beads can also be used for sorting
droplets.
[0260] The present invention provides methods of screening
molecular libraries on beads through limited-dilution-loading and
then chemical or optical release inside of droplets. Provided are
methods for chemical synthesis on a bead and releasing said
chemical attached to the bead using a releasing means (chemical, UV
light, heat, etc) within a droplet, and then combining a second
droplet to the first droplet for further manipulation. For example,
tea-bag synthesis of chemicals on a bead simultaneously with a
means for identifying said bead (using, for example, a mass spec
tag). Using the resulting mixed-chemistry beads in a droplet within
a fluid flow, and exposing the beads to UV light to release the
chemical synthesized from the bead into the droplet environment.
Combining the droplet containing the released chemical with a
droplet containing a cell, and performing a cell-based assay.
Sorting droplets having the desired characteristics (for example,
turn on of a reporter gene), and then analyzing the sorted beads
using mass spectroscopy.
[0261] The device of the present invention can comprise column
separation prior to bead sorting. A device containing a channel
loaded with a separating means for chromatographically sorting the
sample prior to droplet formation. Such separating means could
include size, charge, hydrophobicity, atomic mass, etc. The
separating can be done isocratic or by use of a means for
generating a gradient chemically, (for example using salt or
hydrophobicity), electrically, by pressure, or etc. For example, a
channel is preloaded with Sepharose size exclusion media. A sample
is loaded at one end, and the droplets are formed at an opposing
end. The sample separates by size prior to becoming incorporated
within a droplet.
Sorting Module
[0262] The microfluidic device of the present invention can further
include one or more sorting modules. A "sorting module" is a
junction of a channel where the flow of molecules, cells, small
molecules or particles can change direction to enter one or more
other channels, e.g., a branch channel for delivery to an outlet
module (i.e., collection or waste module), depending on a signal
received in connection with an examination in the detection module.
Typically, a sorting module is monitored and/or under the control
of a detection module, and therefore a sorting module may
"correspond" to such detection module. The sorting region is in
communication with and is influenced by one or more sorting
apparatuses. A sorting apparatus comprises techniques or control
systems, e.g., dielectric, electric, electro-osmotic, (micro-)
valve, etc. A control system can employ a variety of sorting
techniques to change or direct the flow of molecules, cells, small
molecules or particles into a predetermined branch channel. A
"branch channel" is a channel which is in communication with a
sorting region and a main channel. The main channel can communicate
with two or more branch channels at the sorting module or "branch
point", forming, for example, a T-shape or a Y-shape. Other shapes
and channel geometries may be used as desired. Typically, a branch
channel receives molecules, cells, small molecules or particles
depending on the molecule, cells, small molecules or particles
characteristic of interest as detected by the detection module and
sorted at the sorting module. A branch channel can have an outlet
module and/or terminate with a well or reservoir to allow
collection or disposal (collection module or waste module,
respectively) of the molecules, cells, small molecules or
particles. Alternatively, a branch channel may be in communication
with other channels to permit additional sorting.
[0263] The device of the present invention can further include one
or more outlet modules. An "outlet module" is an area of the device
that collects or dispenses molecules, cells, small molecules or
particles after coalescence, detection and/or sorting. The outlet
module can include a collection module and/or a waste module. The
collection module can be connected to a means for storing a sample.
The collection module can be a well or reservoir for collecting and
containing droplets detected to have a specific predetermined
characteristic in the detection module. The collection module can
be temperature controlled. The waste module can be connected to a
means for discarding a sample. The waste module can be a well or
reservoir for collecting and containing droplets detected to not
have a specific predetermined characteristic in the detection
module. The outlet module is downstream from a sorting module, if
present, or downstream from the detection model if a sorting module
is not present. The outlet module may contain branch channels or
outlet channels for connection to a collection module or waste
module. A device can contain more than one outlet module.
[0264] A characteristic of a fluidic droplet may be sensed and/or
determined in some fashion, for example, as described herein (e.g.,
fluorescence of the fluidic droplet may be determined), and, in
response, an electric field may be applied or removed from the
fluidic droplet to direct the fluidic droplet to a particular
region (e.g. a channel). A fluidic droplet is preferably sorted or
steered by inducing a dipole in the uncharged fluidic droplet
(which may be initially charged or uncharged), and sorting or
steering the droplet using an applied electric field. The electric
field may be an AC field, a DC field, etc. For example, with
reference to FIG. 20A, a channel 540, containing fluidic droplet
530 and liquid 535, divides into channel 542 and 544. Fluidic
droplet 530 is uncharged. Electrode 526 is positioned near channel
542, while electrode 527 is positioned near channel 544. Electrode
528 is positioned near the junction of channels 540, 542, and 544.
In FIGS. 20C and 20D, a dipole is induced in the fluidic droplet
using electrodes 526, 527, and/or 528. In FIG. 20C, a dipole is
induced in droplet 530 by applying an electric field 525 to the
droplet using electrodes 527 and 528. Due to the strength of the
electric field, the droplet is strongly attracted to the right,
into channel 544. Similarly, in FIG. 20D, a dipole is induced in
droplet 530 by applying an electric field 525 to the droplet using
electrodes 526 and 528, causing the droplet to be attracted into
channel 542. Thus, by applying the proper electric field, droplet
530 can be directed to either channel 542 or 544 as desired.
[0265] The present invention also provides improvements in the
efficiency, accuracy, and reliability of the preferred dielectric
droplet sorting technique described above. The single sided
dielectric sorting relies on a combination of flow imbalance
between the two exhaust legs and a switchable electric field to
selectively sort out droplets of interest from the main sample
stream. Sorting decisions are made based on some form of real time
measurement of the droplet and its contents. FIGS. 21 and 22 depict
many of the various possible fluid and electrode geometries
possible for single sided dielectric sorting. FIG. 21, Panels A-D
show possible flow channel geometries that can be used in an
asymmetric sorting application. Panel F, illustrates the use of a
barrier, for example, a barrier where no fluid flow passes on its
left side. Note these designs are only conceptual representation of
the fluid channels, and actual designs may differ in absolute and
relative dimensions as determined by one of ordinary skill in the
art.
[0266] FIG. 22 shows the possible electrode geometries used in an
asymmetric sorting application. Panel A shows the use of sharp
tipped electrodes. Panel B shows broad tipped electrodes to
increase the interaction time between the droplets and the electric
field (the tips could be many drop diameters long). Panel C shows
electrodes straddling the collection line. Panel D shows electrodes
on opposite sides of the main channel. Panel E shows an Asymmetric
Electrode Pair (the asymmetry may be present on any of the other
electrode pair layouts as well). Note these designs are only
conceptual representation of the electrodes, and actual designs may
differ in absolute dimensions and electrode shape as determined by
one of ordinary skill in the art. Although the fluid channel
geometry is drawn as a "Y" junction, any of the channel geometries
shown in FIG. 21 could be substituted in these drawings.
[0267] Typically, the flow rate of the collection leg is set to a
value just below the level required to begin pulling droplets into
the collection line (indicated as 40% in the figures, although the
actual value may be differ from this and is dependent on the actual
fluidic and electrode geometry, total flow, as well as droplet size
and composition).
[0268] As an alternative design strategy, the collection leg can be
operated at a flow rate at which the droplets would normally flow
down the Sort collect line (i.e. change the flow splits shown in
the diagrams from 40% collect/60% waste to 60% collect/40% waste),
and keep the electric field energized until a droplet of interest
is detected. At that time, the field would be briefly turned off,
and the droplet would be pulled down the collection leg based on
fluidic forces instead of electrical forces.
[0269] Alternately, a fluidic droplet may be directed by creating
an electric charge (e.g., as previously described) on the droplet,
and steering the droplet using an applied electric field, which may
be an AC field, a DC field, etc. As an example, an electric field
may be selectively applied and removed (or a different electric
field may be applied) as needed to direct the fluidic droplet to a
particular region. The electric field may be selectively applied
and removed as needed, in some embodiments, without substantially
altering the flow of the liquid containing the fluidic droplet. For
example, a liquid may flow on a substantially steady-state basis
(i.e., the average flowrate of the liquid containing the fluidic
droplet deviates by less than 20% or less than 15% of the
steady-state flow or the expected value of the flow of liquid with
respect to time, and in some cases, the average flowrate may
deviate less than 10% or less than 5%) or other predetermined basis
through a fluidic system of the invention (e.g., through a channel
or a microchannel), and fluidic droplets contained within the
liquid may be directed to various regions, e.g., using an electric
field, without substantially altering the flow of the liquid
through the fluidic system.
[0270] In other embodiments, however, the fluidic droplets may be
screened or sorted within a fluidic system of the invention by
altering the flow of the liquid containing the droplets. For
instance, in one set of embodiments, a fluidic droplet may be
steered or sorted by directing the liquid surrounding the fluidic
droplet into a first channel, a second channel, etc.
[0271] In another set of embodiments, pressure within a fluidic
system, for example, within different channels or within different
portions of a channel, can be controlled to direct the flow of
fluidic droplets. For example, a droplet can be directed toward a
channel junction including multiple options for further direction
of flow (e.g., directed toward a branch, or fork, in a channel
defining optional downstream flow channels). Pressure within one or
more of the optional downstream flow channels can be controlled to
direct the droplet selectively into one of the channels, and
changes in pressure can be effected on the order of the time
required for successive droplets to reach the junction, such that
the downstream flow path of each successive droplet can be
independently controlled. In one arrangement, the expansion and/or
contraction of liquid reservoirs may be used to steer or sort a
fluidic droplet into a channel, e.g., by causing directed movement
of the liquid containing the fluidic droplet. The liquid reservoirs
may be positioned such that, when activated, the movement of liquid
caused by the activated reservoirs causes the liquid to flow in a
preferred direction, carrying the fluidic droplet in that preferred
direction. For instance, the expansion of a liquid reservoir may
cause a flow of liquid towards the reservoir, while the contraction
of a liquid reservoir may cause a flow of liquid away from the
reservoir. In some cases, the expansion and/or contraction of the
liquid reservoir may be combined with other flow-controlling
devices and methods, e.g., as described herein. Non limiting
examples of devices able to cause the expansion and/or contraction
of a liquid reservoir include pistons and piezoelectric components.
In some cases, piezoelectric components may be particularly useful
due to their relatively rapid response times, e.g., in response to
an electrical signal.
[0272] In some embodiments, the fluidic droplets may be sorted into
more than two channels. Alternately, a fluidic droplet may be
sorted and/or split into two or more separate droplets, for
example, depending on the particular application. Any of the
above-described techniques may be used to spilt and/or sort
droplets. As a non-limiting example, by applying (or removing) a
first electric field to a device (or a portion thereof), a fluidic
droplet may be directed to a first region or channel; by applying
(or removing) a second electric field to the device (or a portion
thereof), the droplet may be directed to a second region or
channel; by applying a third electric field to the device (or a
portion thereof), the droplet may be directed to a third region or
channel; etc., where the electric fields may differ in some way,
for example, in intensity, direction, frequency, duration, etc. In
a series of droplets, each droplet may be independently sorted
and/or split; for example, some droplets may be directed to one
location or another, while other droplets may be split into
multiple droplets directed to two or more locations.
[0273] In some cases, high sorting speeds may be achievable using
certain systems and methods of the invention. For instance, at
least about 1 droplet per second may be determined and/or sorted in
some cases, and in other cases, at least about 10 droplets per
second, at least about 20 droplets per second, at least about 30
droplets per second, at least about 100 droplets per second, at
least about 200 droplets per second, at least about 300 droplets
per second, at least about 500 droplets per second, at least about
750 droplets per second, at least about 1000 droplets per second,
at least about 1500 droplets per second, at least about 2000
droplets per second, at least about 3000 droplets per second, at
least about 5000 droplets per second, at least about 7500 droplets
per second, at least about 10,000 droplets per second, at least
about 15,000 droplets per second, at least about 20,000 droplets
per second, at least about 30,000 droplets per second, at least
about 50,000 droplets per second, at least about 75,000 droplets
per second, at least about 100,000 droplets per second, at least
about 150,000 droplets per second, at least about 200,000 droplets
per second, at least about 300,000 droplets per second, at least
about 500,000 droplets per second, at least about 750,000 droplets
per second, at least about 1,000,000 droplets per second may be
determined and/or sorted in such a fashion.
[0274] Multiple Measurement Sorting
[0275] In some embodiments, it may be useful to sort droplets based
on two different measurements. For example, one might want to sort
based on the ratio of two signals, sum of two signals, or
difference between two signals. Specifically, this would be useful
for cases when one would like to optimize an enzyme so that it work
one substrate, but not another, or so that it works on two
substrates. This is not easy to do using multiple rounds of
selection on populations of droplets. To overcome this shortcoming
of current sorting technology, the present invention provides a
device comprising multiple channels with the appropriate geometry
to split droplets, perform different experiments on the two
daughter droplets and then reorder so that they pass sequential
through the detector. The sums, ratios or differences in the two
signals can then be calculated before the droplets enter the
sorting bifurcation. An indicator dye or equivalent material may be
added to one or both droplets to indicate when each droplet enters
and leaves the laser. A representative sketch is shown in FIG.
23.
[0276] Sample Recovery
[0277] The present invention proposes methods for recovering
aqueous phase components from aqueous emulsions that have been
collected on a microfluidic device in a minimum number of steps and
in a gentle manner so as to minimize potential damage to cell
viability.
[0278] In one aspect, a stable aqueous sample droplet emulsion
containing aqueous phase components in a continuous phase carrier
fluid is allowed to cream to the top of the continuous phase
carrier oil. By way of nonlimiting example, the continuous phase
carrier fluid can include perfluorocarbon oil that can have one or
more stabilizing surfactants. The aqueous emulsion rises to the top
or separates from the continuous phase carrier fluid by virtue of
the density of the continuous phase fluid being greater than that
of the aqueous phase emulsion. For example, the perfluorocarbon oil
used in one embodiment of the device is 1.8, compared to the
density of the aqueous emulsion, which is 1.0.
[0279] The creamed emulsion is then placed onto a second continuous
phase carrier fluid which contains a de-stabilizing surfactant,
such as a perfluorinated alcohol (e.g., 1H, 1H, 2H,
2H-Perfluoro-1-octanol). The second continuous phase carrier fluid
can also be a perfluorocarbon oil. Upon mixing, the aqueous
emulsion begins to coalesce, and coalescence is completed by brief
centrifugation at low speed (e.g., 1 minute at 2000 rpm in a
microcentrifuge). The coalesced aqueous phase can now be removed
(cells can be placed in an appropriate environment for further
analysis).
[0280] Additional destabilizing surfactants and/or oil combinations
can be identified or synthesized to be useful with this
invention.
Mixing Module
[0281] The microfluidic device of the present invention can further
include one or more mixing modules. Although coalescence of one or
more droplets in one or more coalescence modules can be sufficient
to mix the contents of the coalesced droplets (e.g., through
rotating vortexes existing within the droplet), it should be noted
that when two droplets fuse or coalesce, perfect mixing within the
droplet does not instantaneously occur. Instead, for example, the
coalesced droplet may initially be formed of a first fluid region
(from the first droplet) and a second fluid region (from the second
droplet). Thus, in some cases, the fluid regions may remain as
separate regions, for example, due to internal
"counter-revolutionary" flow within the fluidic droplet, thus
resulting in a non-uniform fluidic droplet. A "mixing module" can
comprise features for shaking or otherwise manipulate droplets so
as to mix their contents. The mixing module is preferably
downstream from the coalescing module and upstream from the
detection module. The mixing module can include, but is not limited
to, the use of channel geometries, acoustic actuators, metal alloy
component electrodes or electrically conductive patterned
electrodes to mix the contents of droplets and to reduce mixing
times for fluids combined into a single droplet in the microfluidic
device. For example, the fluidic droplet may be passed through one
or more channels or other systems which cause the droplet to change
its velocity and/or direction of movement. The change of direction
may alter convection patterns within the droplet, causing the
fluids to be at least partially mixed. Combinations are also
possible.
[0282] For acoustic manipulation, the frequency of the acoustic
wave should be fine tuned so as not to cause any damage to the
cells. The biological effects of acoustic mixing have been well
studied (e.g., in the ink-jet industry) and many published
literatures also showed that piezoelectric microfluidic device can
deliver intact biological payloads such as live microorganisms and
DNA. In an example, the design of the acoustic resonant uses a
Piezoelectric bimorph flat plate located on the side of the carved
resonant in the PDMS slab. The piezoelectric driving waveform is
carefully optimized to select the critical frequencies that can
separate cells in fluids. There are five parameters to optimize
beyond the frequency parameter. Lab electronics is used to optimize
the piezoelectric driving waveform. Afterwards, a low cost circuit
can be designed to generate only the optimized waveform in a
preferred microfluidic device.
[0283] Other examples of fluidic mixing in droplets are described
WO 2004/091763, incorporated herein by reference.
Delay Module
[0284] The microfluidic device of the present invention can further
include one or more delay modules. The "delay module" can be a
delay line. The operation of a microfluidics device where a
reaction within a droplet is allowed to occur for a non-trivial
length of time requires a delay line to increase the residence time
within the device. For reactions demanding extensive residence
time, longer or larger delay lines are required. Accordingly, the
invention provides methods to increase residence times within
microfluidic devices.
[0285] The delay module is in fluid communication with the main
channel or it can be an elongated portion of the main channel
itself. The delay module can be located downstream of the
coalescence module and upstream of the detection module. The delay
module can be a serpentine channel or a buoyant hourglass. The
delay module can further comprise heating and cooling regions. The
heating and cooling regions can be used for performing on-chip,
flow-through PCR as further described herein.
[0286] The channel dimensions and configurations can be designed to
accommodate the required residence time with minimum pressure drops
across the device. For example, to accommodate very long delay
lines within the microfluidic device, the device can comprise a
multilayered PDMS slab which is composed of several patterned PDMS
slabs.
[0287] The channel dimensions can also be designed so as to allow
for required flow, residence time and pressure drop. Some channels
may be required to be very large in width and height. In order to
avoid collapse of the channels, the device includes support posts
within the channel design. In order to reduce dead volume behind
posts and further improve droplet stability, the support posts are
designed to optimize a streamlined flow within the channel. These
designs can include curved features as opposed to sharp edges.
[0288] To allow for longer period of device operation, delay lines
can also be extended to the outside of the chip. The off-chip delay
lines can be tubes within micron-sized internal diameter.
[0289] In order to allow more efficient use of available space and
faster operation, in methods where droplets are charged, after
charging, asymmetric splitting of oil and drops can be accommodated
by siphoning off oil from channels after droplets are charged.
[0290] The delay lines can be in the form of a tower (i.e., a
structure which is vertical with respect to the ambient
gravitational field) as to allow buoyant forces to assist
controlled droplet transport. Known delay lines involve
transporting droplets by emulsifying them in a carrier fluid
flowing in a channel and/or tube. Because the velocity profile of
the carrier fluid through the cross-section of the channel and/or
tube is not uniform, the velocity distribution of the droplets will
not be narrow, which causes the delay time distribution of the
droplets to not be narrow (i.e., some droplets will be delayed more
or less than others).
[0291] The devices of the present invention can also include
buoyancy-assisted microfluidic delay lines. In buoyancy-assisted
microfluidic delay lines, buoyant forces act on droplets emulsified
in a fluid in one or more towers. This can include allowing the
tower to fill for the desired delay time, and then releasing the
droplets. The tower can or can not continue to fill and release
droplets as needed. In this example, one may desire to have a
cylindrical tower section that is capped by a pyramidal funnel
section. The tower can effectively functions as an hourglass.
Droplets that have a density less than their carrier fluid are fed
into the base of the tower, buoyantly rise to the top of the tower
with a substantially uniform velocity distribution, and are
funneled into a functional component of the microfluidic device
(such as a y-branch). Carrier fluid is exhausted at the base of the
tower at the same rate as it is introduced at the apex so that the
net flow of carrier fluid through the delay line is zero. The tower
and funnel sections can have any cross-sectional shape, such as
circular, elliptical, or polygonal. The microfluidic device can
include a tower with adjustable length.
[0292] The device can also include a switching network of twenty
towers to guarantee a delay time dispersion of 5% (because
1/20=0.05). The capacity of each tower is 0.05*T, where T is the
delay time. The concept includes, for example: (a) upon device
start-up, filling the first tower for 0.05*T, but stop-cock its
exhaust, and also have the other nineteen towers closed; (b) after
0.05*T, closing the first tower and filling the second between
0.05*T and 0.10*T; (c) repeating step (b) for the remaining
eighteen towers; (d) at time T, allowing the first tower to
exhaust; (e) at time 1.05*T, stop-cocking the exhaust of the first
tower, allowing the second tower to exhaust, and allowing the first
tower to fill; (f) at time 1.10*T, stop-cocking the exhaust of the
second tower, allowing the third tower to exhaust, closing the
first tower, and allowing the second tower to fill, and (g)
repeating step (f) ad infinitum. More than twenty towers may
provide an even tighter control over the width of the delay time
dispersion. This scheme may require a valve network. This network
of towers can be outside the microfluidic device.
[0293] The delay module can also include channels (e.g. the main
channel) which has an altered geometry which permits the "parking"
(e.g., slowing or stopping) of droplets within the microfluidic
device.
[0294] In the methods provided herein, droplets are able to be
parked in wells or channels at predefined locations. This can be
done by creating discrete well-like indentions in the channel
whereby a droplet `falls` into the well and remains there as the
fluid flows over it, or by using a technique entitled `by-pass
pots` whereby a droplet is used to block a small outlet in a well,
thereby causing the flow to by-pass that droplet-containing
well.
[0295] The instant invention is to use either of these techniques
or any related technique, for example just stopping the drops in a
channel, to position droplets at either random or predefined places
within a microfluidics device. These random or predefined locations
can then be queried at a later time-point for a reaction to have
occurred, or for removal of the droplets using another means such
as resuspension followed by aspiration.
[0296] In one example, a rolling circle amplification reaction is
initiated in droplets, the droplets are then parked within the
chip, and the amplification reaction allowed to proceed for a set
period of time prior to stopping the reaction through the use of
heat. The parked droplets are then dried in situ and the covering
of the chip disassembled from the chip. One or a set of needle-like
devices that are able to be lined up with the droplet parking space
are then placed adjacent to or on top of the dried droplets and a
liquid solution used to resuspend the material in the dried droplet
that has been deposited into the chip, for further downstream
processing.
[0297] In another example, to avoid possible diffusion of reactant
contents from a first and a second set of reactions in droplets,
the first reactions are created in 10 .mu.m droplets, the droplets
are dried within a channel parking space or by-pass pot which is
able to hold a droplet of size larger than 10 .mu.m, and the
droplets are dried in situ. A second set of droplets that are
larger than 10 .mu.m are then allowed to proceed down said channel
and when caught in said parking space or by-pass pot are able to
resuspend the material from the first droplets that are dried along
the walls of the first parking space or by-pass pot. In doing so,
the second droplet is slightly larger than the first and that
ensures that the material along the walls is `captured` by the
second droplet, and not allowed to diffuse away from the first
droplet wall by diffusion. By doing so, use of surfactants becomes
optional in either the first or second droplet formulations.
[0298] The instant invention also provides the following devices
and methods for use in practicing the methods described herein. The
PDMS substrate which comprises a portion of the microfluidic device
can be covered or coated with an adhesive tape or strip that can
removed by peeling. The PDMS substrate can also be bonded by an
ultra thin silica that can be pierced by a set of needles. The
silica may be spin coated or electro-plated onto a thin backing.
Droplets can be dried onto a piece of paper such that can be
detected by a second device to determine the Ncode within the
droplet and to determine whether an amplification reaction has
occurred within the droplet. A plate read comprising dried and
undried spots using either an optical array device, such as found
in high-end cameras or fiber, optic device is also contemplated.
Dry Nitrogen can be utilized to dry the spots by either flowing it
through the channel or placing the device into a dry-N2 chamber.
Channels can be filled with dried nitrogen or salt run underneath
or adjacent to the parking space channels to allow chemical or
physical-type gradients to be set up in the chip. The channel walls
can be coated with Steptavidin and the produced reactants, for
example, DNA biotinylated so that it adheres in situ. Porous beads
deposited into the wells can be used in combination with solutions
without oils to wash the beads by flow, followed by re-depositing
droplets with surfactants to recoat the beads. The wells within the
substrate can be filled with many small beads by loading small
beads into droplets, storing the droplets into individual wells
containing apertures that are slightly smaller than the beads,
breaking the droplets by drying or flow of aqueous solutions with
or without surfactants into the channels and past the beads, and
then re-encapsulating the beads in situ. A set of electrodes within
or adjacent to the microfluidic substrate can be used to fuse two
droplets in a storage/holding space. The electrodes may be
perpendicular to the plane of the channels and either the
electrodes or channels moved so as to allow droplet fusions to
occur.
UV-Release Module
[0299] The microfluidic device of the present invention can further
include one or more UV-release modules. The "UV-release module" is
in fluid communication with the main channel. The UV release module
is located downstream of the inlet module and upstream of the
coalescence module. The UV-module can be a used in bead assays.
Compounds from encapsulated beads can be cleaved in a UV-releasing
module using UV light. Photolabile linkers can be broken down on
demand after a single bead has been encapsulated thus releasing
multiple copies of a single compound into solution. In the cell
based assay disclosed herein the chemical compound assayed is
desired to be in solution in order to penetrate the cell membrane.
Furthermore, to ensure compartmentalization of a single, compound
with a cell the cleavage of the compound from the solid support can
only be done after the bead has been encapsulated. Photocleavable
linkers can be utilized to cleave the compounds of the bead after
drop formation by passing the drop through a UV-release module
(i.e., laser of the appropriate wavelength).
[0300] The present invention also provides methods for chemical
synthesis on a bead and releasing said chemical attached to the
bead using a releasing means (chemical, UV light, heat, etc.)
within a droplet, and then combining a second droplet to the first
droplet for further manipulation. Preferably, the releasing means
is a UV-module. For example, tea-bag synthesis of chemicals on a
bead simultaneously with a means for identifying said bead (using,
for example, a mass spec tag). Using the resulting mixed-chemistry
beads in a droplet within a fluid flow, and exposing the beads to
UV light to release the chemical synthesized from the bead into the
droplet environment. Combining the droplet containing the released
chemical with a droplet containing a cell, and performing a
cell-based assay. Sorting droplets having the desired
characteristics (for example, turn on of a reporter gene), and then
analyzing the sorted beads using mass spectroscopy.
Kits
[0301] As a matter of convenience, predetermined amounts of the
reagents, compound libraries, and/or emulsions described herein and
employed in the present invention can be optionally provided in a
kit in packaged combination to facilitate the application of the
various assays and methods described herein. Such kits also
typically include instructions for carrying out the subject assay,
and may optionally include the fluid receptacle, e.g., the cuvette,
multiwell plate, microfluidic device, etc. in which the reaction is
to be carried out.
[0302] Typically, reagents included within the kit are uniquely
labeled emulsions containing tissues, cells, particles, proteins,
antibodies, amino acids, nucleotides, small molecules, substrates,
and/or pharmaceuticals. These reagents may be provided in
pre-measured container (e.g., vials or ampoules) which are
co-packaged in a single box, pouch or the like that is ready for
use. The container holding the reagents can be configured so as to
readily attach to the fluid receptacle of the device in which the
reaction is to be carried out (e.g., the inlet module of the
microfluidic device as described herein). In one embodiment, the
kit can include an RNAi kit. In another embodiment, the kit can
include a chemical synthesis kit. It will be appreciated by persons
of ordinary skill in the art that these embodiments are merely
illustrative and that other kits are also within the scope of the
present invention.
Methods
[0303] The microfluidic device of the present invention can be
utilized to conduct numerous chemical and biological assays,
including but not limited to, creating emulsion libraries, flow
cytometry, gene amplification, isothermal gene amplification, DNA
sequencing, SNP analysis, drug screening, RNAi analysis,
karyotyping, creating microbial strains with improved biomass
conversion, moving cells using optical tweezer/cell trapping,
transformation of cells by electroporation, .mu.TAS, and DNA
hybridization.
Definitions
[0304] The terms used in this Specification generally have their
ordinary meanings in the art, within the context of this invention
and in the specific context where each term is used. Certain terms
are discussed below, or elsewhere in the specification, to provide
additional guidance to the practitioner in describing the devices
and methods of the invention and how to make and use them. It will
be appreciated that the same thing can typically be described in
more than one way. Consequently, alternative language and synonyms
may be used for any one or more of the terms discussed herein.
Synonyms for certain terms are provided. However, a recital of one
or more synonyms does not exclude the use of other synonyms, nor is
any special significance to be placed upon whether or not a term is
elaborated or discussed herein. All publications, patent
applications, patents, and other references mentioned herein are
incorporated by reference. In the case of conflict, the present
specification, including definitions, will control. In addition,
the materials, methods, and examples are illustrative only and are
not intended to be limiting.
[0305] The invention is also described by means of particular
examples. However, the use of such examples anywhere in the
specification, including examples of any terms discussed herein, is
illustrative only and in no way limits the scope and meaning of the
invention or of any exemplified term. Likewise, the invention is
not limited to any particular preferred embodiments described
herein. Indeed, many modifications and variations of the invention
will be apparent to those skilled in the art upon reading this
specification and can be made without departing from its spirit and
scope. The invention is therefore to be limited only by the terms
of the appended claims along with the full scope of equivalents to
which the claims are entitled.
[0306] As used herein, "about" or "approximately" shall generally
mean within 20 percent, preferably within 10 percent, and more
preferably within 5 percent of a given value or range.
[0307] The term "molecule" means any distinct or distinguishable
structural unit of matter comprising one or more atoms, and
includes for example polypeptides and polynucleotides.
[0308] The term "polymer" means any substance or compound that is
composed of two or more building blocks (`mers`) that are
repetitively linked to each other. For example, a "dimer" is a
compound in which two building blocks have been joined
together.
[0309] The term "polynucleotide" as used herein refers to a
polymeric molecule having a backbone that supports bases capable of
hydrogen bonding to typical polynucleotides, where the polymer
backbone presents the bases in a manner to permit such hydrogen
bonding in a sequence specific fashion between the polymeric
molecule and a typical polynucleotide (e.g., single-stranded DNA).
Such bases are typically inosine, adenosine, guanosine, cytosine,
uracil and thymidine. Polymeric molecules include double and single
stranded RNA and DNA, and backbone modifications thereof, for
example, methylphosphonate linkages.
[0310] Thus, a "polynucleotide" or "nucleotide sequence" is a
series of nucleotide bases (also called "nucleotides") generally in
DNA and RNA, and means any chain of two or more nucleotides. A
nucleotide sequence typically carries genetic information,
including the information used by cellular machinery to make
proteins and enzymes. These terms include double or single stranded
genomic and cDNA, RNA, any synthetic and genetically manipulated
polynucleotide, and both sense and anti-sense polynucleotide
(although only sense stands are being represented herein). This
includes single- and double-stranded molecules, i.e., DNA-DNA,
DNA-RNA and RNA-RNA hybrids, as well as "protein nucleic acids"
(PNA) formed by conjugating bases to an amino acid backbone. This
also includes nucleic acids containing modified bases, for example
thio-uracil, thio-guanine and fluoro-uracil.
[0311] The polynucleotides herein may be flanked by natural
regulatory sequences, or may be associated with heterologous
sequences, including promoters, enhancers, response elements,
signal sequences, polyadenylation sequences, introns, 5'- and
3'-non-coding regions, and the like. The nucleic acids may also be
modified by many means known in the art. Non-limiting examples of
such modifications include methylation, "caps", substitution of one
or more of the naturally occurring nucleotides with an analog, and
internucleotide modifications such as, for example, those with
uncharged linkages (e.g., methyl phosphonates, phosphotriesters,
phosphoroamidates, carbamates, etc.) and with charged linkages
(e.g., phosphorothioates, phosphorodithioates, etc.).
Polynucleotides may contain one or more additional covalently
linked moieties, such as, for example, proteins (e.g., nucleases,
toxins, antibodies, signal peptides, poly-L-lysine, etc.),
intercalators (e.g., acridine, psoralen, etc.), chelators (e.g.,
metals, radioactive metals, iron, oxidative metals, etc.), and
alkylators. The polynucleotides may be derivatized by formation of
a methyl or ethyl phosphotriester or an alkyl phosphoramidate
linkage. Furthermore, the polynucleotides herein may also be
modified with a label capable of providing a detectable signal,
either directly or indirectly. Exemplary labels include
radioisotopes, fluorescent molecules, biotin, and the like.
[0312] The term "dielectrophoretic force gradient" means a
dielectrophoretic force is exerted on an object in an electric
field provided that the object has a different dielectric constant
than the surrounding media. This force can either pull the object
into the region of larger field or push it out of the region of
larger field. The force is attractive or repulsive depending
respectively on whether the object or the surrounding media has the
larger dielectric constant.
[0313] "DNA" (deoxyribonucleic acid) means any chain or sequence of
the chemical building blocks adenine (A), guanine (G), cytosine (C)
and thymine (T), called nucleotide bases, that are linked together
on a deoxyribose sugar backbone. DNA can have one strand of
nucleotide bases, or two complimentary strands which may form a
double helix structure. "RNA" (ribonucleic acid) means any chain or
sequence of the chemical building blocks adenine (A), guanine (G),
cytosine (C) and uracil (U), called nucleotide bases, that are
linked together on a ribose sugar backbone. RNA typically has one
strand of nucleotide bases.
[0314] A "polypeptide" (one or more peptides) is a chain of
chemical building blocks called amino acids that are linked
together by chemical bonds called peptide bonds. A "protein" is a
polypeptide produced by a living organism. A protein or polypeptide
may be "native" or "wild-type", meaning that it occurs in nature;
or it may be a "mutant", "variant" or "modified", meaning that it
has been made, altered, derived, or is in some way different or
changed from a native protein, or from another mutant.
[0315] An "enzyme" is a polypeptide molecule, usually a protein
produced by a living organism, that catalyzes chemical reactions of
other substances. The enzyme is not itself altered or destroyed
upon completion of the reaction, and can therefore be used
repeatedly to catalyze reactions. A "substrate" refers to any
substance upon which an enzyme acts.
[0316] As used herein, "particles" means any substance that may be
encapsulated within a droplet for analysis, reaction, sorting, or
any operation according to the invention. Particles are not only
objects such as microscopic beads (e.g., chromatographic and
fluorescent beads), latex, glass, silica or paramagnetic beads, but
also includes other encapsulating porous and/or biomaterials such
as liposomes, vesicles and other emulsions. Beads ranging in size
from 0.1 micron to 1 mm can be used in the devices and methods of
the invention and are therefore encompassed with the term
"particle" as used herein. The term particle also encompasses
biological cells, as well as beads and other microscopic objects of
similar size (e.g., from about 0.1 to 120 microns, and typically
from about 1 to 50 microns) or smaller (e.g., from about 0.1 to 150
nm). The devices and methods of the invention are also directed to
sorting and/or analyzing molecules of any kind, including
polynucleotides, polypeptides and proteins (including enzymes) and
their substrates and small molecules (organic or inorganic). Thus,
the term particle further encompasses these materials.
[0317] The particles (including, e.g., cells and molecules) are
sorted and/or analyzed by encapsulating the particles into
individual droplets (e.g., droplets of aqueous solution in oil),
and these droplets are then sorted, combined and/or analyzed in a
microfabricated device. Accordingly, the term "droplet" generally
includes anything that is or can be contained within a droplet.
[0318] A "small molecule" as used herein, is meant to refer to a
composition that has a molecular weight of less than about 5 kD and
most preferably less than about 4 kD. Small molecules can be, e.g.,
nucleic acids, peptides, polypeptides, peptidomimetics,
carbohydrates, lipids or other organic or inorganic molecules.
Libraries of chemical and/or biological mixtures, such as fungal,
bacterial, or algal extracts, are known in the art.
[0319] As used herein, "cell" means any cell or cells, as well as
viruses or any other particles having a microscopic size, e.g. a
size that is similar to or smaller than that of a biological cell,
and includes any prokaryotic or eukaryotic cell, e.g., bacteria,
fungi, plant and animal cells. Cells are typically spherical, but
can also be elongated, flattened, deformable and asymmetrical,
i.e., non-spherical. The size or diameter of a cell typically
ranges from about 0.1 to 120 microns, and typically is from about 1
to 50 microns. A cell may be living or dead. Since the
microfabricated device of the invention is directed to sorting
materials having a size similar to a biological cell (e.g. about
0.1 to 120 microns) or smaller (e.g., about 0.1 to 150 nm) any
material having a size similar to or smaller than a biological cell
can be characterized and sorted using the microfabricated device of
the invention. Thus, the term cell shall further include
microscopic beads (such as chromatographic and fluorescent beads),
liposomes, emulsions, or any other encapsulating biomaterials and
porous materials. Non-limiting examples include latex, glass,
orparamagnetic beads; and vesicles such as emulsions and liposomes,
and other porous materials such as silica beads. Beads ranging in
size from 0.1 micron to 1 mm can also be used, for example in
sorting a library of compounds produced by combinatorial chemistry.
As used herein, a cell may be charged or uncharged. For example,
charged beads may be used to facilitate flow or detection, or as a
reporter. Biological cells, living or dead, may be charged for
example by using a surfactant, such as SDS (sodium dodecyl
sulfate). The term cell further encompasses "virions", whether or
not virions are expressly mentioned.
[0320] A "virion", "virus particle" is the complete particle of a
virus. Viruses typically comprise a nucleic acid core (comprising
DNA or RNA) and, in certain viruses, a protein coat or "capsid"
Certain viruses may have an outer protein covering called an
"envelope". A virion may be either living (i.e., "viable") or dead
(i.e., "non-viable"). A living or "viable" virus is one capable of
infecting a living cell. Viruses are generally smaller than
biological cells and typically range in size from about 20-25 nm
diameter or less (parvoviridae, picornoviridae) to approximately
200-450 nm (poxviridae). However, some filamentous viruses may
reach lengths of 2000 nm (closterviruses) and are therefore larger
than some bacterial cells. Since the microfabricated device of the
invention is particularly suited for sorting materials having a
size similar to a virus (i.e., about 0.1 to 150 nm), any material
having a size similar to a virion can be characterized and sorted
using the microfabricated device of the invention. Non-limiting
examples include latex, glass or paramagnetic beads; vesicles such
as emulsions and liposomes; and other porous materials such as
silica beads. Beads ranging in size from 0.1 to 150 nm can also be
used, for example, in sorting a library of compounds produced by
combinatorial chemistry. As used herein, a virion may be charged or
uncharged. For example, charged beads may be used to facilitate
flow or detection, or as a reporter. Biological viruses, whether
viable or non-viable, may be charged, for example, by using a
surfactant, such as SDS.
[0321] A "reporter" is any molecule, or a portion thereof, that is
detectable, or measurable, for example, by optical detection. In
addition, the reporter associates with a molecule, cell or virion
or with a particular marker or characteristic of the molecule, cell
or virion, or is itself detectable to permit identification of the
molecule, cell or virion's, or the presence or absence of a
characteristic of the molecule, cell or virion. In the case of
molecules such as polynucleotides such characteristics include
size, molecular weight, the presence or absence of particular
constituents or moieties (such as particular nucleotide sequences
or restrictions sites). In the case of cells, characteristics which
may be marked by a reporter includes antibodies, proteins and sugar
moieties, receptors, polynucleotides, and fragments thereof. The
term "label" can be used interchangeably with "reporter". The
reporter is typically a dye, fluorescent, ultraviolet, or
chemiluminescent agent, chromophore, or radio-label, any of which
may be detected with or without some kind of stimulatory event,
e.g., fluoresce with or without a reagent. In one embodiment, the
reporter is a protein that is optically detectable without a
device, e.g. a laser, to stimulate the reporter, such as
horseradish peroxidase (HRP). A protein reporter can be expressed
in the cell that is to be detected, and such expression may be
indicative of the presence of the protein or it can indicate the
presence of another protein that may or may not be coexpressed with
the reporter. A reporter may also include any substance on or in a
cell that causes a detectable reaction, for example by acting as a
starting material, reactant or a catalyst for a reaction which
produces a detectable product. Cells may be sorted, for example,
based on the presence of the substance, or on the ability of the
cell to produce the detectable product when the reporter substance
is provided.
[0322] A "marker" is a characteristic of a molecule, cell or virion
that is detectable or is made detectable by a reporter, or which
may be coexpressed with a reporter. For molecules, a marker can be
particular constituents or moieties, such as restrictions sites or
particular nucleic acid sequences in the case of polynucleotides.
For cells and virions, characteristics may include a protein,
including enzyme, receptor and ligand proteins, saccharrides,
polynucleotides, and combinations thereof, or any biological
material associated with a cell or virion. The product of an
enzymatic reaction may also be used as a marker. The marker may be
directly or indirectly associated with the reporter or can itself
be a reporter. Thus, a marker is generally a distinguishing feature
of a molecule, cell or virion, and a reporter is generally an agent
which directly or indirectly identifies or permits measurement of a
marker. These terms may, however, be used interchangeably.
[0323] The invention is further described below, by way of the
following examples. The examples also illustrate useful methodology
for practicing the invention. These examples do not limit the
claimed invention.
Examples
Example 1
[0324] The present invention provides methods for preparing a
library of droplet emulsions, where each of the droplets is of the
same, predetermined size (monodisperse). Further, present invention
provides methods for deterministic lateral displacement for
continuous particle separation, which can occur within droplets on
a microfluidic device.
[0325] Particles in solution are usually separated according to
size by exclusion or hydrodynamic chromatography. In the former, a
sample mixture is injected at one end of a tube packed with porous
beads and then washed through the tube. Particles smaller than the
pore sizes enter the beads, which lengthen their migration path,
and so they are on average eluted later than larger particles.
Zones of particles of a given size broaden, however, because
particles in each zone take many different paths leading to
different retention times. This multipath effect reduces the
resolution of size-exclusion chromatography. In hydrodynamic
chromatography, a sample mixture is driven through a capillary by
hydrodynamic flow, which has a parabolic flow profile. Large
particles cannot intercept the low-velocity fluid near the
capillary wall, and thus on average move faster and become
separated from small particles. Multipath effects also limit the
resolution of hydrodynamic chromatography, because each migration
path samples different velocities in the parabolic flow.
[0326] Recently, Huang et al. Science 304(5673):987-90, 2004 and
Davis et al Proc Natl Acad Sci USA. 103(40):14779-84, 2006
demonstrate a separation process that creates equivalent migration
paths for each particle in a mixture, thereby eliminating multipath
zone broadening. They describe a `lateral displacement` means for
separation of particles in solution based on particle size.
[0327] Lateral displacement means for sizing and separating
droplets in solution (based on droplet size) can be utilized. The
present invention relates to the generation of a microfluidic
device consisting of raised pillars in both columns and rows that
are designed for lateral diffusion. The pillars can be adjusted so
as to be a means for separating droplets of similar sizes from a
fluid containing various sized droplets.
[0328] In an example, a fluid containing oil, water and a
surfactant is mixed so as to create a bulk emulsion. The bulk
emulsion is injected into beginning of a microfluidic lateral
diffusion device and various fractions are collected at the ending
of the device at positions corresponding to specific sizes.
Advantages to this lateral diffusion separation means would be the
isolation of similarly-sized droplets off-line in a fast and facile
manner. Bulk emulsions could be size-selected and then the
resulting emulsions, if desired, combined to create sized libraries
for re-introduction into a microfluidic device. In a further
example, the lateral diffusion microfluidic devices could be
rolled-up into a syringe or designed for parallel processing.
[0329] Recently, devices that exploit both techniques have been
miniaturized with the use of microfabrication technology.
Microfabricated devices have also been designed that inherently
rely on diffusion for separation. Particle mixtures are either
repeatedly subject to spatially asymmetric potentials created by
microelectrodes or driven through arrays of micrometer-scale
asymmetric obstacles to exploit differences in diffusion lengths.
In all of the devices discussed so far, particles in a given zone
have many different migration paths, and diffusion is required for
separation.
[0330] The present invention describes a separation process that
creates equivalent migration paths for each particle in a mixture,
thereby eliminating multipath zone broadening (FIG. 24). FIG. 24.
(Panel A) Geometric parameters defining the obstacle matrix. A
fluid flow is applied in the vertical direction (orange arrow).
(Panel B) Three fluid streams (red, yellow, and blue) in a gap do
not mix as they flow through the matrix. Lane 1 at the first
obstacle row becomes lane 3 at the second row, lane 3 becomes lane
2 at the third row, and so on. Small particles following
streamlines will thus stay in the same lane. (Panel C) A particle
with a radius that is larger than lane 1 follows a streamline
passing through the particle's center (black dot), moving toward
lane 1. The particle is physically displaced as it enters the next
gap. Black dotted lines mark the lanes.
[0331] The separation process uses laminar flow through a periodic
array of micrometer-scale obstacles. Each row of obstacles is
shifted horizontally with respect to the previous row by
.delta..lamda., where .lamda., is the center-to-center distance
between the obstacles (FIG. 24). For convenience, let
.delta..lamda./.lamda. be 1/3. Fluid emerging from a gap between
two obstacles will encounter an obstacle in the next row and will
bifurcate as it moves around the obstacle. Let the flow diverted to
the left of the obstacle be .delta..PHI., where .PHI. is the total
fluid flux going through the gap. If the fluid is confined to move
straight down through the array, .delta. must equal
.delta..lamda./.lamda.. Let us then consider the flow through a gap
to be made up of three lanes, each of which by definition has a
flux of .PHI./3. Because the Reynolds number is low (<10.sup.3
in micrometer-scale environments) and flows are laminar, the
streams in each lane do not cross or mix (FIG. 24B). Notably, as
the lanes go through gaps, their positions relative to the gaps
change. The lanes are represented in each gap by 1, 2, and 3, from
left to right, respectively. Lane 1 becomes lane 3 in the next gap,
lane 2 becomes lane 1, and lane 3 becomes lane 2 (FIG. 24). After
three rows, the three lanes rejoin in their original
configuration.
[0332] Particles that are smaller than the lane width will follow
the streamlines. A particle starting in lane 1 will go through lane
3 (right lane with respect to the gap) in the second row, lane 2
(middle lane) in the third row, and back to lane 1 (left lane) in
the fourth row (FIG. 24B). In fact, particles starting from any of
the three lanes will go back to the original lane assignment after
three rows, so that net migration is in the average flow direction.
This motion is called the "zigzag mode." In practice, particles can
diffuse into an adjacent lane. However, the microscopic path for
all lanes is equivalent, unlike the multiple paths particles take
when moving through a column of porous beads. In contrast to the
smaller particles, a particle with a radius larger than the width
of lane 1 at a gap will behave differently in the array. This is
because the center of the particle cannot "fit" into lane 1 in a
gap. As such a particle from lane 2 in one gap moves into the
subsequent gap, expecting to move through the gap in lane 1, the
particle will be "bumped" and its center will thus be displaced
into lane 2 (FIG. 24C). The particle will then flow with the fluid
in lane 2. This process is repeated every time a large particle
approaches a row of obstacles, so that the particle remains in lane
2 as it moves down through the array. This transport pattern is
called the "displacement mode." This is also applicable to
electrophoresis by considering ion flows instead of fluid
flows.
[0333] FIG. 25 shows High-resolution separation of fluorescent
microspheres with diameters of 0.80 um (green), 0.90 um (red), and
1.03 um (yellow), with a matrix of varying gap size. Whereas the
shift in registry and the lattice constants of the matrix remain
the same, the obstacle diameters are changed to create gaps, d, of
different sizes, which are labeled on the left side of the
fluorescent image. The red bars on the fluorescence profile
represent the width of the peaks (SD), and the black bars label the
1% inhomogeneity in the bead population. a.u., arbitrary units.
[0334] FIG. 26 is a schematic illustrating the separation by
deterministic lateral displacement in an array of microposts, with
an example row shift fraction of one-third. This shift creates
three equal flux streamlines. The dashed lines are the boundaries
between the streamlines, which are assigned an index in the gaps
between the posts. Paths of particles both smaller and larger than
the critical threshold are depicted with green and red dotted lines
respectively. Small particles stay within a flow Stream and large
particles are displaced at each obstacle. G is the clear spacing
between the gap, is the center-to-center post separation, and d is
the relative shift of the post centers in adjacent rows.
[0335] These described methods allow for the quick and efficient
formation of uniformed sized droplet emulsion libraries for further
use on a microfluidic device of the present invention.
Example 2
[0336] The present invention provides methods for performing
polymerase chain reaction (PCR). PCR can be performed on a
drop-by-drop basis in a microfluidic device according to the
present invention. A monolithic chip can be provided wherein the
heating and cooling lines are built into the chip and a sorting
means is provided. Advantages of performing PCR in droplets on such
a chip are that the chip is disposable and the reaction can be
repeated without cleaning the device between reactions.
Furthermore, the chip provides a convenient way of getting all the
components to perform PCR in the droplets in the right
concentration. Additionally, the PCR is more efficient because the
heat transfer is more efficient due to the small volume. This
provides for shorter incubation/residence 15 times. Droplets
containing the nucleic acids, all PCR primers, and, if present,
beads are generated one at a time at rates between 100 and 20,000
droplets per second. The droplets can then be sent through a
serpentine path between heating and cooling lines to amplify the
genetic material inside the droplets. Upon exiting the device the
droplets may be sent for further on-chip or off-chip processing,
directed into another chip, or the emulsion may be broken to
release the PCR product. If present, beads may be harvested by
passing the emulsion through a filtration device, sedimentation, or
centrifugation.
[0337] The width and depth of the channel can be adjusted to set
the residence time at each temperature, which can be controlled to
anywhere between less than a second and minutes. At a typical rate
of 1000 drops per second, 1 million strands of DNA can be amplified
in approximately 20 minutes on one device. A typical flow rate of
250 .mu.L/hour would correspond to 1000 drops of 50 microns in
diameter being generated every second. Flow rates and droplet sizes
can be adjusted as needed by controlling the nozzle geometry.
[0338] The present invention also provides methods for performing
dideoxynucleotide sequencing reactions on a microfluidic device.
Chain terminator sequencing (Sanger sequencing) is well known to
those of ordinary skill in the art. DNA template preparation,
cycling sequencing and preparing extension products for
electrophoresis are related techniques and also well known to those
of skill in the art. Applied Biosystems' "Automated DNA Sequencing:
Chemistry Guide" 2000 is an excellent resource covering these
techniques and is incorporated herein by reference in its
entirety.
[0339] One method is to sequencing PCR templates which can include
single amplification PCR or nested and semi-nested PCR strategies.
In the simplest PCR sequencing case, the target DNA is amplified
with a single set of primers and then sequenced using the same
primers. For many samples, this works well. For the samples that do
not work well with this method, optimization of the PCR
amplification may be required. Optimizing the PCR minimizes the
presence of nonspecific product bands and ensures adequate yield. A
single PCR amplification is also compatible with the use of a
sequencing primer that binds internally (semi-nested or nested) to
one or both of the PCR primers. This can be helpful if primer-dimer
(primer oligomerization) artifacts are a problem.
[0340] If difficulty with more complex samples, such as bacterial
genomic DNA, is encountered a nested or semi-nested PCR can be
used. These techniques are useful when the target is present in
small quantity. They offer more specificity, which provides
superior sequencing data with reduced background signal. Both
nested and semi-nested PCR require two amplifications. The first
amplification is identical for nested and semi-nested, but the
second amplification differs as described below. Amplify with one
set of PCR primers, which converts a complex sample (such as
bacterial genomic DNA) into a non-complex sample consisting of the
first PCR product and some side products. Nested PCR: Amplify 1% or
less of the first PCR reaction product using a second set of PCR
primers that hybridize at positions internal to the first set.
Semi-nested PCR: Only one primer of the second set of PCR primers
is internal. The other primer is one of the original PCR
primers.
[0341] A PCR primer can be synthesized with a universal sequencing
primer binding site added to the 5' end (e.g., see Appendix E in
Applied Biosystems' "Automated DNA Sequencing: Chemistry Guide" for
universal primer sequences). This allows any PCR product to be
sequenced with universal primers. Universal-tailed PCR primers
enable the use of commercially available dye-labeled sequencing
primers. This technique is also useful with dye terminator
chemistries, because universal sequencing primers have good
annealing characteristics. However, the longer PCR primers add to
the overall cost of the reactions. Using universal-tailed primers
sometimes results in primer oligomerization. As these products have
priming sites present, they can result in noisy data for the first
20-100 bases. Redesigning the PCR primer, optimizing the PCR
amplification further, and employing Hot Start methods can help
overcome this situation.
[0342] After PCR amplification, the resulting PCR product is in
solution along with PCR primers, dNTPs, enzyme, and buffer
components. The method used to prepare the PCR product for
sequencing depends on the amounts of these components that are
carried over and on the chemistry used for sequencing. Excess PCR
primers carried over from the amplification reaction compete with
the sequencing primer for binding sites and reagents in the
sequencing reaction. This carryover of PCR primers presents more of
a problem in dye terminator chemistries because the dye label is
incorporated into the extension product after the primer anneals to
the template. If more than one primer is present, multiple
dye-labeled sequence ladders are generated, resulting in noisy
data. Excess dNTPs from the amplification reaction can affect the
balance of the sequencing reaction, resulting in decreased
termination in shorter extension fragments.
[0343] Nonspecific PCR products include primer-dimer artifacts and
secondary PCR products. The presence of any significant quantity of
either in a PCR product can result in poor quality sequencing data.
Nonspecific PCR products behave as templates in the sequencing
reaction and produce extension products, which results in noisy
data. These products often can be visualized on an agarose gel
before sequencing. If they are present, the PCR amplification
should be optimized and repeated before sequencing. Use of a nested
or semi-nested sequencing primer can also allow good sequence data
to be obtained. Alternatively, the PCR product of interest can be
purified by agarose gel electrophoresis.
[0344] There are several ways to minimize contaminants in a PCR
amplification: PCR optimization (Innis and Gelfand, 1990): (1)
Amount of starting DNA; (2) Careful primer design; (3) Primer
concentration, (4) Enzyme concentration, (5) Magnesium ion (Mg2+)
concentration, (6) Nucleotide concentration; (7) Buffer
composition; (8) Number of cycles; (9) pH; (10) Manual Hot Start
method; (11) AmpliTaq Gold.RTM. DNA Polymerase as an automatic Hot
Start and/or (12) Limiting dNTPs and primers. All of these methods
increase the specificity of the PCR amplification and decrease the
amount of contaminants that can interfere with a sequencing
reaction.
[0345] There are several methods for purifying PCR products: (1)
Column purification; (2) Ethanol precipitation; and/or (3) Gel
purification.
[0346] An alternative to one of the more stringent purification
methods listed above is treatment of PCR products with shrimp
alkaline phosphatase (SAP) and exonuclease I (Exo I) before
sequencing. The SAP/Exo I procedure degrades nucleotides and
single-stranded DNA (primers) remaining after PCR (Werle et al.,
1994). This procedure is particularly useful in cases where
limiting concentrations of primers and nucleotides cannot be used
for direct PCR sequencing.
[0347] FIG. 27 shows one embodiment for a DNA sequencing chip
design. Template DNA and primers are combined at step `add 1` and
the reaction is incubated at 95.degree. C. for a hot start
(position 1). The reaction then cycles 20-30 times (position 2)
before the addition of SAP and ExoI at `add 2.` The reaction is
incubated at 37.degree. C. for a pre-defined time-period and then
the SAP and Exol enzymes are inactivated at 95.degree. C. (position
`4`). The SAP/ExoI procedure degrades nucleotides and
single-stranded DNA (primers) remaining after PCR. The universal
sequencing primers, ddNTPs and buffers are added at `add 3,` and
the PCR sequencing reaction is allowed to proceed at position `5.`
The final reaction product is collected and can be stored
off-chip.
[0348] Step Action
[0349] 1. For each sample, combine the following: [0350] SAP (1
Unit/.mu.L), 2 .mu.L [0351] Exo I (10 Units/.mu.L), 0.2 .mu.L
[0352] Deionized water, 6.0 .mu.L [0353] Note In general this
procedure works well using 0.5 units of each enzyme per microliter
of PCR products used. The procedure seems to work equally well with
or without the use of SAP buffer, so this has been excluded in this
protocol.
[0354] 2. Add 4.0 .mu.L of PCR product to the above mix.
[0355] 3. Incubate at 37.degree. C. for 1 hour.
[0356] 4. Incubate at 72.degree. C. for 15 minutes to inactivate
the enzymes.
[0357] The recommended DNA quantities for sequencing reactions are
shown in Table 3-1 below.
TABLE-US-00002 TABLE 3-1 Recommended Ranges of DNA Template
Quantity for Each Chemistry Cycle Sequencing Chemistry Rhodamine
Fluorescein/ Template Dye dRhodamine BigDye Rhodamine BigDye PCR
product: Terminator Terminator Terminator Dye Primer Primer 100-200
bp 1-3 ng 1.-3 ng 1-3 ng 2-5 ng 2-5 ng 200-500 bp 3-10 ng 3-10 ng
3-10 ng 5-10 ng 5-10 ng 600-1000 bp 5-20 ng 5-20 ng 5-20 ng 10-20
ng 10-20 ng 1000-2000 bp 10-40 ng 10-40 ng 10-40 ng 20-50 ng 20-50
ng >2000 bp 40-100 ng 40-100 ng 40-100 ng 50-150 ng 50-150 ng
single-stranded 100-250 ng 50-100 ng 50-100 ng 150-300 ng 150-400
ng double-stranded 200-500 ng 200-500 ng 200-500 ng 300-600 ng
200-800 ng coamid, BAC 0.5-2.0 .mu.g not recommended 0.6-1.0 .mu.g
0.5-2.0 .mu.g 0.5-1.0 .mu.g bacterial genomic DNA not recommended
2-3 .mu.g not recommended
[0358] PCR protocols that limit amounts of primers and dNTPs allow
the product of the reaction to be used for sequencing with no
purification. This is usually carried out by setting up the PCR
amplification with 5-10 pmol of primers and 20-40 .mu.M dNTPs, so
that most of the primers and dNTPs are exhausted during
amplification. If the yield of the desired PCR product is high and
the product is specific, i.e., it produces a single band when
analyzed by agarose gel electrophoresis, the sample can be diluted
before sequencing and will give good results. The dilution ratio
depends on the concentration of your PCR product and needs to be
determined empirically (start with 1:2 and 1:10 dilutions with
deionized water). When you limit concentrations of primers and
dNTPs and dilute the PCR products, the PCR parameters have to be
robust. Direct PCR sequencing is most useful in applications where
the same target is being amplified and sequenced repeatedly and PCR
conditions have been optimized. Direct PCR sequencing can be done
with dye primer chemistries. With dye terminator chemistries, it is
much more critical that the PCR primers be consumed. Excess PCR
primers will be extended and labeled by the cycle sequencing
reaction, resulting in noisy data. Direct PCR sequencing does not
work for XL PCR because limiting amounts of primers and dNTPs
cannot be used. The PCR product should be purified or the excess
primers and nucleotides should be degraded by SAP/Exo I
treatment.
Example 3
[0359] The present invention provides methods for performing
isothermal-type amplification methods on a microfluidic device.
Isothermal amplification is an alternative to the standard PCR
techniques described herein. Isothermal amplification is used to
reduce the relative amount of background DNA in a sample. Primers
are generally used in a constant temperature means of
amplification. Isothermal amplification is applicable for SNP
detection. Once the DNA is amplified by isothermal amplification
there are several well-known means for detecting which nucleotide
polymorphism is present. These include, but are not limited to;
allele specific primer extension, oligonucleotide ligation assay,
mini-sequencing, fluorescence polarization, etc. Isothermal
amplification is also applicable for DNA sequencing preparation.
The isothermally-amplified DNA can be attached to a solid phase
within a droplet or placed within a parking space on chip. The
beads or parking spaces can be accessed and the amplified DNA used
for a DNA sequencing reaction. Further, isothermal amplification is
applicable for gene expression analysis. Isothermal amplification
can be used to monitor gene expression by the measurement of the
amount of cDNA produced in a quantitative fashion. Many methods for
isothermal amplification are known in the art, including but not
limited to the following examples.
[0360] Rolling circle amplification (RCA). A DNA polymerase extends
a primer on a circular template, generating tandemly linked copies
of the complementary sequence of the template (Fire & Xu,
1995). The TempliPhi amplification process using rolling circle
amplification is known in the art. In the process, random hexamer
primers anneal to the circular template DNA at multiple sites.
Phi29 DNA polymerase extends each of these primers. When the DNA
polymerase reaches a downstream-extended primer, strand
displacement synthesis occurs. The displaced strand is rendered
single-stranded and available to be primed by more hexamer primer.
The process continues, resulting in exponential, isothermal
amplification.
[0361] Transcription mediated amplification (TMA). An RNA
polymerase is used to make RNA from a promoter engineered in the
primer region, a reverse transcriptase to produce complementary DNA
from the RNA templates and RNase H to remove the RNA from cDNA
(Guatelli et al, 1990).
[0362] Strand-displacement amplification (SDA). A restriction
endonuclease is used to nick the unmodified strand of its target
DNA and the action of an exonuclease-deficient DNA polymerase to
extend the 30 end at the nick and displace the downstream DNA
strand (Walker et al, 1992). Strand-displacement amplification is
known in the art.
[0363] Helicase-dependent amplification (HDA). A DNA helicase is
used to generate single-stranded templates for primer hybridization
and subsequent primer extension by a DNA polymerase. Schematic
diagram of HAD is shown in FIG. 28. Two complementary DNA strands
are shown as two lines: the thick one is the top strand and the
thin one is the bottom strand. 1: A helicase (black 30 triangle)
separates the two complementary DNA strands, which are bound by SSB
(grey circles). 2: Primers (lines with arrow heads) hybridize to
the target region on the ssDNA template. 3: A DNA polymerase
(squares with mosaic patterns) extends the primers hybridized on
the template DNA. 4: Amplified products enter the next round of
amplification.
[0364] One example is emulsion-based sample preparation. Random
libraries of DNA fragments are generated by shearing an entire
genome and isolating single DNA molecules by limiting dilution.
See, FIG. 29. Specifically, sequencing reactions such as those
performed by Solexa, 454 Life Sciences and others involve randomly
fragmenting the entire genome, adding specialized common adapters
to the fragments, capturing the individual fragments on their own
beads and, within the droplets of an emulsion, clonally amplifying
the individual fragment (FIG. 29a, 29b). Unlike in current
sequencing technology, their approach does not require subcloning
or the handling of individual clones; the templates are handled in
bulk within the emulsions. Typically, about 30% of the beads will
have DNA, producing 450,000 template-carrying beads per emulsion
reaction.
[0365] Sample preparation and DNA sequencing is shown in FIG. 29.
Panel A, Genomic DNA is isolated, fragmented, ligated to adapters
and separated into single strands (top left). Fragments are bound
to beads under conditions that favor one fragment per bead, the
beads are captured in the droplets of a PCR-reaction-mixture-in-oil
emulsion and PCR amplification occurs within each droplet,
resulting in beads each carrying ten million copies of a unique DNA
template (top, second from the left). The emulsion is broken, the
DNA strands are denatured, and beads carrying single-stranded DNA
clones are deposited into wells of a fiber-optic slide (bottom
left). Smaller beads carrying immobilized enzymes required for
pyrophosphate sequencing are deposited into each well (bottom,
second from the left). Panel B, Microscope photograph of emulsion
showing droplets containing a bead and empty droplets. The thin
arrow points to a 28-mm bead; the thick arrow points to an
approximately 100-mm droplet. Panel C, Scanning electron micrograph
of a portion of a fiber-optic slide, showing fiber-optic cladding
and wells before bead deposition. Panel D, The sequencing
instrument consists of the following major subsystems: a fluidic
assembly. Panel E, a flow chamber that includes the well-containing
fiber-optic slide. Panel F, a CCD camera-based imaging assembly.
Panel G, and a computer that provides the necessary user interface
and instrument control.
[0366] Another example is sequencing in fabricated picolitre-sized
reaction vessels. One method uses sequencing by synthesis
simultaneously in open wells of a fiber-optic slide using a
modified pyrosequencing protocol that is designed to take advantage
of the small scale of the wells. The fiber optic slides are
manufactured by slicing of a fiber-optic block that is obtained by
repeated drawing and fusing of optic fibers. At each iteration, the
diameters of the individual fibers decrease as they are hexagonally
packed into bundles of increasing cross-sectional sizes. Each
fiber-optic core is 44 .mu.m in diameter and surrounded by 2-3
.mu.m of cladding; etching of each core creates reaction wells
approximately 55 .mu.m in depth with a centre-to-centre distance of
50 .mu.m (FIG. 29c), resulting in a calculated well size of 75 pl
and a well density of 480 wells per square mm. The slide,
containing approximately 1.6 million wells, is loaded with beads
and mounted in a flow chamber designed to create a 300-.mu.m high
channel, above the well openings, through which the sequencing
reagents flow (FIG. 29d). The unetched base of the slide is in
optical contact with a second fiber optic imaging bundle bonded to
a charge-coupled device (CCD) sensor, allowing the capture of
emitted photons from the bottom of each individual well (FIG. 29d).
A three-bead system has been developed and the components optimized
to achieve high efficiency on solid support. The combination of
picoliter-sized wells, enzyme loading uniformity allowed by the
small beads and enhanced solid support chemistry enabled users to
develop a method that extends the useful read length of
sequencing-by-synthesis to 100 bases.
[0367] In the flow chamber cyclically delivered reagents flow
perpendicularly to the wells. This configuration allows
simultaneous extension reactions on template-carrying beads within
the open wells and relies on convective and diffusive transport to
control the addition or removal of reagents and by-products. The
timescale for diffusion into and out of the wells is on the order
of 10 s in the current configuration and is dependent on well depth
and flow channel height. The timescales for the signal-generating
enzymatic reactions are on the order of 0.02-1.5 s. The current
reaction is dominated by mass transport effects, and improvements
based on faster delivery of reagents are possible. Well depth was
selected on the basis of a number of competing requirements: (1)
wells need to be deep enough for the DNA-carrying beads to remain
in the wells in the presence of convective transport past the
wells; (2) they must be sufficiently deep to provide adequate
isolation against diffusion of by-products from a well in which
incorporation is taking place to a well where no incorporation is
occurring; and (3) they must be shallow enough to allow rapid
diffusion of nucleotides into the wells and rapid washing out of
remaining nucleotides at the end of each flow cycle to enable high
sequencing throughput and reduced reagent use. After the flow of
each nucleotide, a wash containing a pyrase is used to ensure that
nucleotides do not remain in any well before the next nucleotide
being introduced.
[0368] Another example is base calling of individual reads.
Nucleotide incorporation is detected by the associated release of
inorganic pyrophosphate and the generation of photons. Wells
containing template-carrying beads are identified by detecting a
known four-nucleotide `key` sequence at the beginning of the read.
Raw signals are background-subtracted, normalized and corrected.
The normalized signal intensity at each nucleotide flow, for a
particular well, indicates the number of nucleotides, if any, that
were incorporated. This linearity in signal is preserved to at
least homopolymers of length eight. In sequencing by synthesis a
very small number of templates on each bead lose synchronism (that
is, either get ahead of, or fall behind, all other templates in
sequence). The effect is primarily due to leftover nucleotides in a
well (creating `carry forward`) or to incomplete extension.
Typically, a carry forward rate of 1-2% and an incomplete extension
rate of 0.1-0.3% is seen. Correction of these shifts is essential
because the loss of synchronism is a cumulative effect that
degrades the quality of sequencing at longer read lengths.
[0369] Methods have demonstrated the simultaneous acquisition of
hundreds of thousands of sequence reads, 80-120 bases long, at 96%
average accuracy in a single run of the instrument using a newly
developed in vitro sample preparation methodology and sequencing
technology. With Phred 20 as a cutoff, they are able to show that
their instrument is able to produce over 47 million bases from test
fragments and 25 million bases from genomic libraries. Recent work
on the sequencing chemistry and algorithms that correct for
crosstalk between wells suggests that the signal distributions will
narrow, with an attendant reduction in errors and increase in read
lengths. In preliminary experiments with genomic libraries that
also include improvements in the emulsion protocol, one is able to
achieve, using 84 cycles, read lengths of 200 bases with accuracies
similar to those demonstrated here for 100 bases. On occasion, at
168 cycles, individual reads that are 100% accurate over greater
then 400 bases have been generated.
[0370] Isothermal amplification reactions, as described above, have
shown great promise generating high yields with great fidelity.
However, an associated drawback arises from the tendency of the
polymerase to generate spurious, non-template amplification
products when reactions are conducted in the absence of template
DNA. Additionally, our application utilizes high microfluidic
throughput in conjunction with limiting DNA template dilutions to
amplify single template molecules. As a result, 10 the number of
empty reaction droplets increases considerably, comprising 90% or
more of the total droplet population following Poisson
distributions. Non-template amplification (hereafter NTA) in even a
small fraction of the total droplets can confound amplification
detection strategies based on laser interrogation of intercalating
dyes, thus this issue must be resolved. To address this problem in
the art, the present invention provides the use of mixed modified
and standard hexamer primers in microfluidic reactions to retard
NTA while allowing template-based amplification to proceed.
[0371] Previous work has attempted to reduce NTA through
incorporation of nitroindole bases (Loakes and Brown 1994; Loakes,
Hill et al. 1997) in the random primers (Lage, Leamon et al. 2003)
or reducing reaction volumes to 600 nL (Hutchison, Smith et al.
2005). Unfortunately, modified nitroindole primers have proven
difficult to replicate, and often have the effect of significantly
reducing the overall rate and yield of the amplifications in which
they are incorporated. Low volume reactions conducted in multiplate
wells have encountered difficulties stemming from dispensation of
low volumes, and associated issues of sample evaporation, well to
well contamination, etc.
[0372] The modified primers of the present invention containing
nitroindoles and C3 non-replicable elements were studied in an
effort to reduce NTA both in bulk and microfluidic reactions. Both
nitroindoles and C3 non-replicable elements were found to be
effective in reducing NTA, with primers containing two 5'
nitroindoles most effective in NTA suppression. However, increased
NTA suppression was tightly linked with reduced yield in template
amplification reactions. Amplifications using a ratio of
nitroindole to random hexamer primers generated a range of both
template and non-template amplification yields, with a 15:85 ratio
of nitroindole to random hexamers generating template yields
commensurate with random hexamers primers alone, but generating
little if any spurious product in the absence of template.
Example 4
[0373] The PCR and isothermal amplifications described herein can
be very useful in performing single nucleotide polymorphism
analysis. A Single Nucleotide Polymorphism, or SNP, is a small
genetic change, or variation, that can occur within a person's DNA
sequence. The genetic code is specified by the four nucleotide
"letters" A (adenine), C (cytosine), T (thymine), and G (guanine).
SNP variation occurs when a single nucleotide, such as an A,
replaces one of the other three nucleotide letters--C, G, or T.
[0374] An example of a SNP is the alteration of the DNA segment
AAGGTTA to ATGGTTA, where the second "A" in the first snippet is
replaced with a "T". On average, SNPs occur in the human population
more than 0.1 percent of the time. Because only about 3 to 5
percent of a person's DNA sequence codes for the production of
proteins, most SNPs are found outside of "coding sequences". SNPs
found within a coding sequence are of particular interest to
researchers because they are more likely to alter the biological
function of a protein. Because of the recent advances in
technology, coupled with the unique ability of these genetic
variations to facilitate gene identification, there has been a
recent flurry of SNP discovery and detection.
[0375] Although many SNPs do not produce physical changes in
people, scientists believe that other SNPs may predispose people to
disease and even influence their response to drug regimens.
Currently, there is no simple way to determine how a patient will
respond to a particular medication. A treatment proven effective in
one patient may be ineffective in others. Worse yet, some patients
may experience an adverse immunologic reaction to a particular
drug. Today, pharmaceutical companies are limited to developing
agents to which the "average" patient will respond. As a result,
many drugs that might benefit a small number of patients never make
it to market.
[0376] In the future, the most appropriate drug for an individual
could be determined in advance of treatment by analyzing a
patient's SNP profile. The ability to target a drug to those
individuals most likely to benefit, referred to as "personalized
medicine", would allow pharmaceutical companies to bring many more
drugs to market and allow doctors to prescribe individualized
therapies specific to a patient's needs.
[0377] Finding single nucleotide changes in the human genome seems
like a daunting prospect, but over the last 20 years, biomedical
researchers have developed a number of techniques that make it 25
possible to do just that. Each technique uses a different method to
compare selected regions of a DNA sequence obtained from multiple
individuals who share a common trait. In each test, the result
shows a physical difference in the DNA samples only when a SNP is
detected in one individual and not in the other. Currently,
existing SNPs are most easily studied using microarrays.
Microarrays allow the simultaneous testing of up to hundreds of
thousands of separate SNPs and are quickly screened by
computer.
[0378] The race among pharmaceutical companies today is to apply
new system genomics approach to identify novel targets and validate
these targets in the most efficient fashion. SNP research will
provide fundamental understanding of many polygenic diseases, thus
providing new therapeutic targets. As groups have performed
genome-wide scans and other large studies that require the
genotyping of thousands of SNPs and samples, a need for
high-throughput SNP genotyping has become essential.
[0379] The microfluidic device of the present invention is capable
of performing at least 10,000 SNP analysis per second, such that a
full genome scan (i.e., 100K SNPs) with 10.times.
overrepresentation can be performed in less than an hour. The speed
and efficiency permitted using the devices and methods of the
present invention will significantly lower the associated costs and
reagent consumption for performing SNP analysis.
Example 5
[0380] The PCR and isothermal amplifications described herein can
be very useful in providing necessary sample preparation processes
for commercial available DNA sequencers, such as the Solexa's 1G
sequencer, which relies upon immobilized DNA for a substrate. In
one embodiment, single molecules can be amplified using PCR primers
treated with moieties used for surface immobilization, then flow
the PCR positive droplets across the surface of the slide, forming
a packed emulsion. The emulsion can then be broken, and the primers
allowed to bind to the slide due the presence of the appropriate
coating to bind the PCR products.
[0381] The Solexa 1G sequencer currently sequences amplified
material that has been amplified in place, on primers bound to the
slide, by bridge amplification. In this process, template DNA is
flowed across the slide surface at very low concentrations, and
adapters previously ligated to each template hybridize to
complimentary primers attached to the slide in any one of eight
lanes. Once hybridized, the primers are subjected to bridge
amplification, a version of PCR amplification that utilizes
immobilized primers--the product of the reaction is a patch of DNA
immobilized to the slide. Several risks are encountered when
amplifying DNA in this matter--the process is exquisitely sensitive
to DNA concentration--if too much DNA is used, the DNA patches will
be generated too closely, or even overlap, generating mixed signals
during subsequent sequencing. If too little DNA is used, the DNA
patches will be present at a very low density, and insufficient
sequence may be generated during the run. As the sequencing
reactions take 72 hours, and no titration runs are conducted to
test the DNA concentrations prior to amplification, the potential
loss of time and money is considerable. Additionally, neither
single molecule amplification nor bridge amplification are very
efficient, and bridge amplification has an upper and lower size
limitation, generating products only within a particular length
range.
[0382] The present invention provides methods to overcome this
limitations. In one embodiment, a Solexa slide can be coated with
any of the compounds commonly used to permit binding and
immobilization (e.g., carboxy-esters, streptavidin, Igg, gold,
etc.). PCR reactions could be performed as described in the instant
microfluidic device using primers modified with the appropriate
binding moiety (5' amines, 5' biotins, 5' DNPs or 5' Thiols,
respectively) to efficiently amplify PCR products in solution which
could then be efficiently and easily bound to the Solexa slide for
subsequent sequencing. The amplification is quite straight forward,
conducted with a limiting dilution of template and a set of primer
pairs compatible with the adapters ligated to the Solexa templates
through their standard sample preparation process. One of the
primer pairs would possess a 5' binding moiety as described
earlier, only one of the pair as this will permit removal of the
opposing strand and the generation of single stranded immobilized
templates on the slide. Once amplification has been conducted, and
the positive droplets sorted, the droplets can be flowed onto each
of the lanes of the Solexa slide. Proper spacing between the
droplets can be obtained by mixing droplets containing only buffer
or immiscible oil in with the PCR positive droplets at a ratio
sufficient to ensure that the PCR positive droplets are rarely
proximal to each other. Once each lane has been packed with
droplets, the droplets can be broken through the application of
electrical field and the PCR products allowed to bind to the slide
in the same geographic area that the droplet had occupied. The
immobilized templates can be rendered single stranded through the
application of basic washes, temperature etc. This will permit the
rapid amplification of PCR fragments and their subsequent
density-controlled deposition onto the Solexa chip for
sequencing.
Example 6
[0383] The present invention provides methods for detecting the
presence and/or sequence of nucleic acids in low copy number in
droplets on a microfluidic device. The detection of a specific
nucleic acid sequence present in a sample by probing the sample
with a complementary sequence of nucleic acids is a well known
technique. Nucleic acids are highly specific in binding to
complementary nucleic acids and are thus useful to determine
whether a specific nucleic acid is present in a sample. One must
know the sequence of the specific nucleic acid to be detected and
then construct a probe having a complementary nucleic acid sequence
to the specific nucleic acid sequence.
[0384] Since nucleic acid probes are highly specific, it is
preferable in some situations to probe the nucleic acid sequence
itself rather than the protein produced by the nucleic acid
sequence. As a particular example, a diagnostic method based solely
on protein detection would be unreliable for determining the
presence of infectious particles of hepatitis B virus, due to the
presence of significant levels of non-infectious antigen particles
which lack the DNA genome. In another example, the various subtypes
of human papilloma virus found in either pre-cancerous or benign
cervical tumors can be distinguished only by the use of nucleic
acid probe hybridization. Also, the specific genetic makeup of an
AIDS virus makes it certain that an assay based on the presence of
an AIDS virus specific nucleic acid sequence would be superior as a
diagnostic.
[0385] The naturally-occurring high number of ribosomal RNA, up to
100,000 copies per cell, has been used by GenProbe to facilitate
diagnosis of certain bacterial pathogens, such as Legionella and
Mycoplasma, using nucleic acid probes. However, this strategy
cannot be used with non-cellular pathogens, such as viruses, or
with probed nucleic acid sequences with low copy numbers. Copy
number is a particular problem with the development of a nucleic
acid probe method for the detection of AIDS virus, where the
integrated provirus may be present in less than one of ten thousand
peripheral blood lymphocytes. Thus, if the particular nucleic acid
sequence suspected to be present in a sample could be amplified,
the copy number problem could be circumvented and probe assays
could be more readily used.
[0386] In a normal biological sample, containing only a few cells,
and consequently only a few copies of a particular gene, it is
necessary to utilize an amplification process in order to overcome
the 5 copy number problem.
[0387] One method to amplify is to `grow out` the sample, that is,
to arrange conditions so that the living biological material
present in the sample can replicate itself. Replication could
increase the quantity of nucleic acid sequences to detectable
levels. In the food industry, for example, in order to test
processed food for the food-poisoning bacteria Salmonella, food
samples must be incubated for a number of days to increase the
quantity of nucleic acid copy numbers. In clinical samples,
pathogens must also be allowed to increase their number by growing
out over some considerable time.
[0388] Current methods utilize a process in which a sample
suspected of containing a target DNA sequence is treated with
oligonucleotide primers such that a primer extension product is
synthesized which in turn serves as a template, resulting in
amplification of the target a DNA sequence. The primer extension
product is separated from the template using heat denaturation.
Current methods also include a process for amplifying a target DNA
sequence having two separate complementary strands. The process
includes treating the strands with primers to synthesize extension
products, separating the primer extension products from the
templates, and in turn using the primer extension products as
templates.
[0389] Both of the above methods require either manual or
mechanical participation and multi-step operations by the user in
the amplification process and are restricted to amplifying DNA
only. The steps involved in these methods require the user to heat
the sample, cool the sample, add appropriate enzymes and then
repeat the steps. The temperature changes cause the enzymes to
loose their activity. Hence, the user is required to repeatedly
supplement the amplification mixture with aliquots of appropriate
enzymes during the amplification process.
[0390] The present invention provides methods for detecting the
presence and/or sequence of nucleic acids in low copy number in
droplets on a microfluidic device. In one embodiment of the
invention, a nucleotide/peptide nucleic acid (pna) probe (oligo
probe) can be tethered such that when it binds to a template DNA
molecule in low copy number located inside an aqueous emulsion
(i.e., droplet) it turns on or activates an enzyme. By way of
nonlimiting example, an alkaline phosphatase conjugate can be
placed on one and of the low copy number nucleotide, and an
inhibitor to alkaline phosphatase on the other end (like a
molecular beacon). When the oligo probe binds to the low copy
number template the inhibitor is removed from the enzyme and the
enzyme turns over the substrate. The tethers can be a protein
complementation assay wherein the binding of the oligo probe to the
low copy number template causes the enzyme to be active.
[0391] Various other embodiments are described herein and should
not be considered as limiting to the invention. Example 1: Taqman
chews a beta-gal alpha protein attached at the 3' end of an oligo
probe thereby releasing free alpha subunit to bind to omega
fragment in solution. Example 2: Two oligo probes sit down on the
low copy number template adjacent to each other, thereby bringing
two subunits of a protein complementing assay reagent together.
Example 3: A Taqman-like enzyme that releases an active moiety can
also be used. The active moiety can include, for example, an enzyme
that becomes activated upon release from the oligo probe, or a
fluorescent group that is quenched while tethered to the oligo
probe. The use of a double-strand specific nuclease that will chew
up the probe only when the probe is bound, thereby releasing active
enzyme or fluorescent substrates. Example 4: The probe has a
fluorescent group attached such that the detected hybridization
causes the release of the fluorescent group a la Taqman. Example 5:
The probe has an inactive enzyme attached such that the detected
hybridization causes the release of the active enzyme by a
Taqman-type release. Example 6: The probe has an inactive
complementing enzyme attached such that the detected hybridization
causes the release of the active moiety of the enzyme to be able to
complement. Example 7: Two probes have inactive enzyme moieties
attached such that the detected hybridization causes the
complementation and activation of the enzyme. Example 8: Two probes
come together and allow a Fluorescence Resonance Energy Transfer
(FRET) reaction to occur. This would require a FRET-oligo library.
Almost all SNP or transcriptional profiling method may be amenable
to this concept.
[0392] Many assays are conducted on microfluidic devices are
including, but not limited to, protein-protein, antibody-antigen,
nucleic acid-protein, nucleic acid-nucleic acid, ligand-protein,
ligand nucleic acid, ligand-ligand, eukaryotic or prokaryotic cell
surface moiety-second moiety, the measurement of two or more
receptors on the surface of an eukaryotic or prokaryotic cell, the
development of three-hybrid type systems using tandem fusions,
interactor-cofactor, etc. Many other types of interactions are also
known that can be adapted to the system. Assays incorporating
complementation assays can be used in both proteomics and
genomics.
[0393] Currently, these assay methods require methods require
>10K fluorescein molecules to detect interaction/binding. In an
embodiment, the present invention provides methods which reduce the
number of interacting proteins by amplifying the signal of
molecules that do interact. In preferred embodiments of some
assays, stable emulsions may not be needed. An advantage is that we
can eliminate surfactants and stabilizing additives which can
affect protein activity within droplets.
[0394] Likewise, one could conceivably look for loss of
complementation in any of the above assays. This loss or gain of
complementation can be a function of physical (e.g., heat, light)
or chemical additions to, or formulation of the droplets. These
interactions include, but are not limited to, protein-protein,
antibody-antigen, nucleic acid-protein, nucleic acid-nucleic acid,
ligand-protein, ligand-nucleic acid, ligand-ligand, eukaryotic or
prokaryotic cell surface moiety-second moiety, the measurement of
two or more receptors on the surface of an eukaryotic or
prokaryotic cell, the development of three-hybrid type systems
using tandem fusions, interactor-cofactor, etc. Many other types of
interactions are also known that can be adapted to the system.
Assays incorporating complementation assays can be used in both
proteomics and genomics.
[0395] The amount of each interacting partner may be with-in drop
quantifiable by genetically or chemically coupling a reporter
molecule (e.g., a dye or quantum dot, GFP protein) to one and or
the other. Similarly, the complementation assay described for
enzymatic amplification can use one of several different
complementing proteins such that the concentration of each partner
can be calculated within the droplet by using different enzyme
substrates added to the droplets at the same or differing time.
Timing of substrate addition is not critical and one of skill in
the art would readily recognize that addition can be done at
different times. `Killing` by various denaturants, protease, etc.
is also within the purview of the skilled artisan.
[0396] In an embodiment, complementation assays can be used to add
a specific addition to, for example, an IVT synthesized protein. As
an example, the s-peptide of RNaseA and the S protein wherein the S
peptide is genetically fused to the IVT-generated Ab and the S
protein, upon binding to the S peptide activates the RNaseA
activity and thereby stops further IVT synthesis. Similarly, any
two complementing interactors can be used to generate an
activity.
[0397] By quantifying the amount of interactors in a droplet it may
be possible to derive interaction kinetics (affinity and
disassociation constants as examples). In an embodiment, the
present invention provides methods which can allow the
quantification of proteins below that which can be seen by
fluorescent spectroscopy in the absence of amplification.
Alternatively, amplification may also not be 20 needed if one can
genetically add a quantified number of reporters to the end of a
molecule. For example, genetically fusing 10 GFP proteins onto the
end of a protein would thereby increase the fluorescence intensity
10-fold. Similarly, a series of small complementing moieties can be
fused onto the end of a protein and there obviate the need for long
genetic fusions. As an example, a series of 10 s peptides spaced
apart by a linker would be able to each `grab hold` of an S protein
to generate an increased signal over that which can be achieved by
a single enzyme. Other examples include either biotin or
biotin-binding protein mimetic and streptavidin or avidin, FLAG
tags, poly histidines, complementing GFP, etc. Another example
includes Qcoding the droplets.
[0398] FIGS. 30 and 31 show the current method for isolating
antibodies on a microfluidic device. In the current method, DNA
beads are made using bulk emulsion PCR; DNA-containing beads
preferably isolated before loading onto a microfluidic device. The
antigen can be <20 kD, (preferably <10 kD) and labeled with
an appropriate dye, (preferably with several dye-molecules). It may
even be preferable to put a poly-lysine tail onto the antigen to
increase signal (but be concerned about quenching). The antigen is
formulated into the bead-containing droplets at a concentration of
100 nm to allow proper sensitivity in the droplet (use of
multiple/different dyes may allow this concentration to drop). In
some situations it is possible to add antigen at the same time as
the IVT solution.
[0399] FIG. 32 shows the method of the present invention for
isolating antibodies on the microfluidic device. The right panel is
a diagram of individual steps proposed to amplify signal of
interacting antibody and antigen. The left panel is a schematic as
would be designed for a chip to be used on microfluidic device.
[0400] FIG. 33 shows the genetic selection for full length antibody
clones. A genetic selection can be used to enrich for full-length
antibody clones by transforming E. coli and selecting for clones
able 5 to grow on medium in which a suitable sugar is the only
carbon source.
Example 7
[0401] The present invention provides a microfluidic device
topology and implementation that merges the functionality of a
first microfluidic substrate with that of a second microfluidic
substrate by using forced withdrawal and reinjection into the same
fluidic port. In current multi-step assays, the following steps
must be performed to complete a "two step" experiment: (1)
Installation of the first microfluidic substrate; (2) Installation
of all first stage reagents; (3) Priming of all fluid lines and
stabilization of the device operation; (4) Passive connection of a
storage container to the instrument after device has been
stabilized; (5) Disconnection of the storage container from the
first device when collection complete; (6) Incubation of the
collected emulsion; (7) Removal of the first device from the
instrument; (8) Cleaning of the fluid lines needed for the second
step of the experiment; (9) Installation of a second device to the
instrument; (10) Connection of all second stage reagents, including
the emulsion collected during the first stage; (11) Priming of the
fluidic connections to the second device prior to running the
second half of the measurement; and (12) Collection/readout of the
second stage.
[0402] The methods of the present invention replaces current
methodology of multi-step assays with the following: (1)
Installation of the first microfluidic substrate; (2) Installation
of all first and second stage reagents, including the first stage
storage container (if it is not already connected); (3) Priming and
stabilization of the fluidic lines and device; (4) Controlled
collection of the first stage combined droplets by actively
withdrawing some fraction of the oil and all of the generated
emulsion into the storage container; (5) Incubation of the
collected emulsion; (6) Startup and reinjection of the collected
droplets back into the second half of the device; and (8)
Collection/readout of the second stage. FIG. 34 depicts a schematic
representation of this device topology.
[0403] Elimination of the handling of the collected emulsion has
significant benefits beyond simplifying the user interaction with
the instrument. Contaminants have the potential to ruin the
experiment, and any extra handling and connection/disconnection
increase the probability that contaminants will be introduced into
the instrument.
Example 8
[0404] Gene silencing through RNAi (RNA-interference) by use of
short interfering RNA (siRNA) has emerged as a powerful tool for
molecular biology and holds the potential to be used for
therapeutic gene silencing. Short hairpin RNA (shRNA) transcribed
from small DNA plasmids within the target cell has also been shown
to mediate stable gene silencing and achieve gene knockdown at
levels comparable to those obtained by transfection with chemically
synthesized siRNA (T. R. Brummelkamp, R. Bernards, R. Agami,
Science 296, 550 (2002), P. J. Paddison, A. A. Caudiy, G. J.
Hannon, PNAS 99, 1443 (2002)). Possible applications of RNAi for
therapeutic purposes are extensive and include silencing and
knockdown of disease genes such as oncogenes or viral genes.
[0405] Many assays are conducted on microfluidic devices are
including, but not limited to, protein-protein, antibody-antigen,
nucleic acid-protein, nucleic acid-nucleic acid, ligand-protein,
ligand-nucleic acid, ligand-ligand, eukaryotic or prokaryotic cell
surface moiety-second moiety, the measurement of two or more
receptors on the surface of an eukaryotic or prokaryotic cell, the
development of three-hybrid type systems using tandem fusions,
interactor-cofactor, etc. Many other types of interactions are also
known that can be adapted to the system. However, there is a need
in the art for improved methods of RNAi screening, quickly and
accurately.
[0406] The present invention provides methods for the screening of
lethal and synthetic lethal RNAi-induced phenotype on a
microfluidic device. The present invention utilizes a lentiviral
library of RNAi where each virus has a unique 60-nt identifying
barcode bracketed on either side with nucleotide sequences common
to all vectors.
[0407] The analysis of lethal and synthetic lethal RNAi-induced
phenotypes occurs in two steps. In the first step, the viral
library is combined in bulk and infected, also in bulk, into an
appropriate host strain. The molar amount of each of the different
lentivirus in the library is pre-determined by sequencing on, for
example, an appropriate instrument or by gene expression analysis
on a microfluidic device. Post infection, the treated cells are
collected and the 60-nt barcode is amplified from chromosomal DNA
using PCR primers based on the bracketing sequence. In the second
step, the PCR amplification product is added to a microfluidic
device and analyzed against a labeled droplet library wherein the
labeled droplets contain lentiviral-barcode-quantification reagents
(e.g., molecular beacons, Taqman probes, etc.) against each of said
lentiviral barcodes. A gene-expression analysis-like analysis is
performed to quantify the amount of each lentiviral barcode-type in
the treated cells. An absence or significant decrease of any
lentiviral barcode in the amplified product can be assumed to be
due to the death of that barcode-containing lentivirus in the
treated cells. In an embodiment, the products within the droplets
can also be amplified.
[0408] GFP or additional transcription analysis can also occur in
two steps. In step one, the viral library is combined in bulk and
infected, also in bulk, into an appropriate host strain. The molar
amount of each of the different lentivirus in the library is
pre-determined by sequencing on, for example, an appropriate
instrument or by gene expression analysis on a microfluidic device.
Post infection, the treated cells are i) collected in bulk, ii)
sorted using a phenotype able to be sorted in a microfluidic device
(e.g., GFP expression, cell-surface marker, low-copy cell-surface
marker, etc.) and iii) the 60-nt barcode is amplified from
chromosomal DNA using PCR primers based on the bracketing sequence.
In the second step, the PCR amplification product is added to a
microfluidic device and analyzed against a labeled droplet library
wherein the labeled droplets contain
lentiviral-barcode-quantification reagents (e.g., molecular
beacons, Taqman probes, etc.) against each of said lentiviral
barcodes. A gene-expression analysis-like analysis is performed to
quantify the amount of each lentiviral barcode-type in the treated
cells. An absence or significant decrease of any lentiviral barcode
in the amplified product can be assumed to be due to the death of
that barcode-containing lentivirus in the treated cells.
Example 9
[0409] Many diseases are associated with particular chromosomal
abnormalities. For example, chromosomes in cancerous cells
frequently exhibit aberrations called translocations, where a piece
of one chromosome breaks off and attaches to the end of another
chromosome. Identifying such chromosome abnormalities and
determining their role in disease is an important step in
developing new methods for diagnosing many genetic disorders.
Traditional karyotyping using Giemsa staining allows scientists to
view the full set of human chromosomes in black and white, a
technique that is useful for observing the number and size of the
chromosomes. However, there is a need in the art for improved
methods of karyotyping, quickly and accurately.
[0410] The present invention provides methods for karyotyping.
Preferably, the karotyping screens occur within droplets on a
microfluidic device. Currently, scientists cannot accurately
identify many translocations or other abnormalities using only a
black and white karyotype. Spectral karyotyping (SKY) is a
laboratory technique that allows scientists to visualize all 23
pairs of human chromosomes at one time, with each pair of
chromosomes painted in a different fluorescent color. By using SKY,
they can easily see instances where a chromosome, painted in one
color, has a small piece of a different chromosome, painted in
another color, attached to it.
[0411] Through the use of droplet-based methods, chromosomes can be
captured within droplets without having to worry about
shear-forces. The chromosomes can then be passed through a `neck
down` to stretch them out. Labeling prior to loading, with either
Giemsa stain or oligonucleotide probes, can be used to karyotype
the DNA as it flows.
[0412] The present invention provides methods of using SKY probes
to `paint` individual chromosomes. Also provided is a method used
by flow cytometrists for the preparation of chromosomes prior to
flow analysis, including flow sorting. The present invention
provides methods which allow the adaptation of these methods for
use on a microfluidic device.
[0413] SKY involves the preparation of a large collection of short
sequences of single-stranded DNA called probes. Each of the
individual probes in this DNA library is complementary to a unique
region of one chromosome; together, all of the probes make up a
network of DNA that is complementary to all of the chromosomes
within the human genome. Each probe is labeled with a fluorescent
molecule that corresponds to the chromosome to which it is
complementary. For example, probes that are complementary to
chromosome 1 are labeled with yellow molecules, while those that
are complementary to chromosome 2 are labeled with red molecules,
and so on. When these probes are mixed with the chromosomes from a
human cell, the probes hybridize, or bind, to the DNA in the
chromosomes. As they hybridize, the fluorescent probes essentially
paint the set of chromosomes in a rainbow of colors. Scientists can
then use computers to analyze the painted chromosomes to determine
whether any of them exhibit translocations or other structural
abnormalities. See, FIG. 35.
[0414] Prior to analysis chromosomes can be prepared as described
in Bee Ling Ng and Nigel P. Carter "Factors Affecting Flow
Karyotype Resolution. Cytometry" Part A 69A:1028-1036 (2006) as
follows: [0415] 1. Arrest cells at metaphase using 0.1 lg/ml
demecolcine for optimal amount of time, dependent on the cell cycle
time of the cell lines. (Approximately 5 h for suspension, 16 h for
adherent cell lines and 4 h for LPS stimulated B lymphocyte
culture). [0416] 2. Harvest cells and centrifuge at 289 g for 5
min. Remove supernatant. [0417] 3. Resuspend cell pellet in 5 ml of
hypotonic solution (75 mM KCl, 10 mM MgSO4, 0.2 mM spermine, 0.5 mM
spermidine, pH 8.0) and incubate at room temperature for 10 min.
[0418] 4. Centrifuge cell suspension at 289 g for 5 min. Remove
supernatant. [0419] 5. Resuspend cell pellet in 3 ml of ice cold
polyamine isolation buffer (PAB, containing 15 mM 20 Tris, 2 mM
EDTA, 0.5 mM EGTA, 80 mM KCl 3 mM dithiothreitol, 0.25% Triton
X-100, 0.2 mM spermine, 0.5 mM spermidine, pH 7.50) and vortex for
20 s. [0420] 6. Briefly centrifuge chromosome suspensions at 201 g
for 2 min. Filter supernatant through 20 lm mesh filter. [0421] 7.
Stain chromosomes overnight with 51 g/ml of Hoechst, 401 g/ml
chromomycin A3 and 10 mM MgSO4. [0422] 8. To the stained chromosome
suspension, add 10 mM of sodium citrate and 25 mM of sodium
sulphite 1 h before flow analysis.
[0423] The present invention also provides methods of sorting
chromosomes for karyotyping wherein individual chromosomes are
sorted. This sorting can be performed after chromosome-specific
identification (such as hybridization of labeled probes) so as to
enrich a population for one or more specific chromosomes. This
enriched population can be used in DNA sequencing reactions.
[0424] The Giemsa-stained and/or labeled-probe-hybridized
chromosomes can be sent through a constriction of a channel on a
microfluidic device to detect the areas of stain and/or label as a
genetic `bar-code` to identify regions of translocation, etc. on
individual chromosomes.
[0425] Identification of chromosomes and karyotyping can be used
after enrichment of specific cell-types, for example i) fetal cells
from maternal blood, or ii) cancer cells from human blood.
Example 10
[0426] The present invention provides microbial strains with
improved biomass conversion and methods of preparing such strains.
Biomass is organic matter such as plant matter, i.e., trees,
grasses, agricultural crops, or other biological material such as
animal material. It can be used as a solid fuel, or converted into
liquid or gaseous forms, for the production of electric power,
heat, chemicals, or fuels. Biomass can also be used in formulating
other commercial products in other industrial sectors such as
textiles, food supply, environmental, communication, housing, etc.
For example, biofuel development seeks the development of new
microbial strains with improved biomass conversion to ethanol.
[0427] Researchers have been applying sophisticated metabolic
engineering techniques to develop microorganisms that can more
effectively ferment the sugars in biomass. Lignocellulosic biomass
contains five carbon sugars such as xylose (from the hemicellulose)
as well as the more "common" six carbon sugars such as glucose
found in grains. This makes fermentation and other bioprocessing
far more challenging. While some biorefinery scenarios will take
advantage of the different sugar streams to produce multiple
products, others will be more cost effective if all the sugars can
coferment in a single set of equipment. Accordingly, researchers
are developing microorganisms that can coferment all the sugars in
biomass in order to improve ethanol production economics. With
industrial partners, researchers are working to develop designer
strains of microorganisms for biomass conversion of specific
feedstocks, feedstreams, and processes. Thus, there is a need for
devices and methods for the rapid engineering of new microbial
strains with improved biomass conversion.
[0428] The present invention provides a microfluidic device in
which to formulate a mutant bacterial, yeast, or fungi strain which
can be used for biomass energy conversion. The microorganism strain
can be engineered, e.g., by recombinant methods, to include at
least one nucleic acid sequence encoding one or more polypeptides
of interest, wherein the mutant strain expresses the polypeptides
of interest at a higher level than the corresponding non-mutant
strain under the same conditions.
[0429] In one embodiment, the nucleic acid sequence can be operably
linked to an expression-regulating region selected from the group
consisting of a promoter sequence associated with cellulase
expression, xylanase expression, or gpdA expression. In another
embodiment, the nucleic acid sequence can further be optionally
linked to a secretion signal sequence.
[0430] In one embodiment, the nucleic acid sequence can be a
heterologous nucleic acid sequence selected from heterologous
polypeptide-encoding nucleic acid sequences, heterologous signal
sequences, or heterologous expression-regulating sequences, or
combinations thereof. For instance, the nucleic acid sequence can
be a heterologous signal sequence, e.g., a secretion signal
sequence. Alternatively, the nucleic acid sequence can be a
heterologous expression-regulating region, e.g., an inducible
promoter or a high expression promoter.
[0431] The polypeptides of interest can be homologous peptides and
are expressed in the mutant strain at a higher level than in the
corresponding non-mutant strain under the same conditions. In one
embodiment, the polypeptides of interest can be selected from one
or more of carbohydrate-degrading enzymes, proteases, lipases,
esterases, other hydrolases, oxidoreductases, and transferases. In
yet another embodiment, the polypeptides of interest can be
selected from one or more of fungal enzymes that allow production
or overproduction of primary metabolites, organic acids, secondary
metabolites, and antibiotics. These fungal sequences can include
secretion signal sequences, for example, and can be selected from
one or more of cellulase, .beta.-galactosidase, xylanase,
pectinase, esterase, protease, amylase, polygalacturonase or
hydrophobin. Alternatively, the fungal sequences can include one or
more fungal expression-regulating regions. Preferably, the
polypeptides of interest exhibit optimal activity and/or stability
at a pH above 6, and/or have more than 70% of its activity and/or
stability at a PH above 6.
[0432] The mutant microorganism can further include a selectable
marker. The selectable marker can confer resistance to a drug, for
example, or relieve a nutritional defect.
[0433] In another embodiment, the microorganism can be mutated via
mutagenesis. Mutagenesis can be achieved, for example, by one or
both of UV irradiation or chemical mutagenesis. For example, in one
embodiment mutagenesis can include exposing a microorganism to UV
irraditation, exposing it to N-methyl-N'-nitro-N-nitrosoguanidine,
and exposing it again to UV irradiation.
[0434] The present invention also provides methods for creating
microbial strains with improved biomass conversion. In one
embodiment, the method includes providing a microfluidic device
made of a microfabricated substrate. The microfabricated substrate
can have a plurality of electrically addressable, channel bearing
modules integrally arranged so as to be in fluid communication with
each other, thereby forming at least one main channel adapted to
carry at least one continuous phase fluid. The method further
includes flowing a buffer, a microbe library, and a media (either
in separate solutions or all together in one solution) through a
first inlet channel into the main channel of the microfabricated
substrate such that one or more droplets is formed in the
continuous phase fluid; flowing a substrate through a second inlet
channel into the main channel of the microfabricated substrate such
that one or more droplets is formed in said continuous phase fluid;
coalescing the droplets containing the microbe library with the
droplets containing the substrate as the droplets pass through a
coalescence module, thereby producing a NanoRefinery; interrogating
the NanoRefinery for a predetermined characteristic within a
detection module on the microfabricated substrate; and collecting
the NanoRefineries containing the microbes of interest in a
collection module on the microfabricated substrate. An assay
system, e.g., a means by which to determine whether a desired
product has been produced, or a means by which to determine the
absence of a starting substrate material, can also be incorporated
into one of the droplets or the NanoRefinery. The assay system can
be added either before, after, or simultaneously with the addition
of the substrate.
[0435] In one embodiment, the assay system is a dye that can
measure the amount of sugar in a solution. In another embodiment,
the microbe library can include one or more of DNA, bacteria, yeast
or fungi. The substrate can include biomass, which can include one
or more of fermentation broth, cellulose or other polysaccharide,
or plant lignan.
[0436] The present invention further provides methods for degrading
or converting biomass into one or more products. In one embodiment,
the method includes treating the biomass with an effective amount
of a recombinant microorganism, wherein the recombinant
microorganism expresses or overexpresses one or more heterologous
sequences encoding enzymes that degrade or convert the biomass into
one or more products. In one embodiment, the biomass can include
plant cell wall polysaccharides. In another embodiment, the
products can include one or more of the commodity chemicals or
secondary commodity chemicals used to produce one or more of the
Intermediates or finished products and consumer goods listed in
FIGS. 36 and 37.
Example 11
[0437] The present invention provides methods of screening for
enzymes with improved activity. As an example, at least one cell
(prokaryotic or eukaryotic) is deposited into a droplet and the
cells are allowed to secrete a substance for which a homogeneous
assay is available. For a specific example, an individual Bacillus
subtilis cell from a mutagen-treated culture is deposited within a
30 micron growth-medium containing droplet, the resulting droplets
are collected and allowed to incubate overnight. The bacterium
secretes a protease into the droplet. The droplets containing the
Bacilli are then individually merged with an assay droplet
containing a protease-cleavable dye-labeled peptide. The uncleaved
peptide is colorless, while the cleaved peptide becomes red. The
droplets are 15 incubated on chip for a sufficient time such as to
allow color formation. Droplets that are red are sorted. The
collected sorted droplets are then plated onto solid growth medium
and the resulting colonies, after overnight incubation, represent
individual clonal isolates from the droplets.
[0438] In addition, the assay droplets can be sorted based upon a
specific activity, for example enzymes that are more active,
indicated by a more intense red droplet after a specific period of
time. In addition, the conditions within the droplet can be changed
during the merging of the two droplets to assay conditions which
may itself not be permissive for the bacteria. For example the pH
within the droplet is altered in order to find mutant enzymes that
work better under either acidic or alkaline conditions. Or the
droplets can be heated such that enzymes that are more heat
resistant are identified.
[0439] The merging of the droplets can be right after the
individual cell is placed into the droplet or after further
incubation.
[0440] Another method of the instant invention is as described
above, except that the cells are lysed before the assay step in
order to release the contents of the cell into the droplet.
[0441] In other embodiments, the substrate can be added with- or
simultaneously formulated from two or more separate reagent streams
with the contained within a droplet. For a specific example,
macrophage cells are washed in buffer and incubated with an
enzyme-conjugated anti-cell-surface antibody. The cells are then
individually loaded into droplets formulated at the same time, with
the enzyme substrate. The amount of enzyme substrate turned over
within the droplet will be proportional to the number of enzyme
molecules within the droplet, which is proportional to the number
of antibodies bound to the macrophage surface. By careful
calibration it should be possible to estimate the number of
cell-surface molecules attached to the cell surface.
* * * * *