U.S. patent application number 14/214203 was filed with the patent office on 2015-01-22 for cell sorting system and methods.
The applicant listed for this patent is CELULA, INC.. Invention is credited to Keunho Ahn, William F. Butler, John Francis, Benjamin Lai, Philippe Marchand, Eugene Tu, Haichuan Zhang, Yi Zhang.
Application Number | 20150024476 14/214203 |
Document ID | / |
Family ID | 39872606 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150024476 |
Kind Code |
A1 |
Butler; William F. ; et
al. |
January 22, 2015 |
CELL SORTING SYSTEM AND METHODS
Abstract
Apparatus and Methods are provided for a microfabricated
fluorescence activated cell sorter based on a switch for rapid,
active control of cell routing through a microfluidic channel
network. This sorter enables low-stress, highly efficient sorting
of populations of small numbers of cells (i.e., 1000-100,000
cells). The invention includes packaging of the microfluidic
channel network in a self-contained plastic cartridge that enables
microfluidic channel network to macro-scale instrument
interconnect, in a sterile, disposable format. Optical and/or
fluidic switching forces are used alone or in combination to effect
switching.
Inventors: |
Butler; William F.; (La
Jolla, CA) ; Zhang; Haichuan; (San Diego, CA)
; Marchand; Philippe; (Poway, CA) ; Ahn;
Keunho; (La Jolla, CA) ; Zhang; Yi; (San
Diego, CA) ; Francis; John; (San Diego, CA) ;
Lai; Benjamin; (San Diego, CA) ; Tu; Eugene;
(San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CELULA, INC. |
San Diego |
CA |
US |
|
|
Family ID: |
39872606 |
Appl. No.: |
14/214203 |
Filed: |
March 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11781848 |
Jul 23, 2007 |
8691164 |
|
|
14214203 |
|
|
|
|
60925563 |
Apr 20, 2007 |
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Current U.S.
Class: |
435/288.7 |
Current CPC
Class: |
G01N 15/1484 20130101;
Y10T 137/86509 20150401; G01N 2015/149 20130101; B01L 2300/0874
20130101; B01L 2200/0652 20130101; Y10T 436/118339 20150115; B01L
3/502776 20130101; B01L 3/502761 20130101; B01L 2300/0864 20130101;
Y10T 436/2575 20150115; B01L 2400/0487 20130101; G01N 33/5005
20130101; B01L 2400/0454 20130101; Y10T 137/87161 20150401; B01L
3/5088 20130101; G01N 15/1459 20130101; C12M 47/04 20130101 |
Class at
Publication: |
435/288.7 |
International
Class: |
G01N 33/50 20060101
G01N033/50 |
Claims
1-24. (canceled)
25. An integrated structure for microfluidic analysis and sorting
comprising: a cartridge, the cartridge comprising an optical
window, a plurality of reservoirs, including at least: a sample
reservoir, a fluid reservoir, a waste reservoir, and a target
collection reservoir, a chip, the chip including at least: a sample
inlet channel, the cell inlet channel being fluidically coupled to
the sample reservoir, one or more fluid inlet channels, the fluid
inlet channels being fluidically coupled to the fluid reservoir, a
detection region, a branched sorting region, and at least two
outlet channels including at least a waste channel and a target
channel, waste channel being fluidically coupled to the waste
reservoir and the target channel being coupled to the target
collection reservoir, the chip being disposed adjacent the optical
window, a lid, the lid including at least: a pneumatic pressure
port, the port having an inlet and being coupled to at least one of
the sample reservoir and the fluid reservoir, and a filter disposed
between the inlet of the pneumatic pressure port and at least one
of the sample reservoir and the fluid reservoir, and a manifold,
the manifold coupling pneumatic pressure from a source to the
pneumatic pressure port without intervening tubing.
26. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the sample reservoir is conical.
27. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the sample reservoir is tapered.
28. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the sample reservoir further includes an
insert.
29. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the insert is a polypropylene insert.
30. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the lid is plastic.
31. The integrated structure for microfluidic analysis and sorting
of claim 30 wherein the lid is acrylic plastic.
32. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the lid includes separate pneumatic pressure
ports for the sample reservoir and the fluid reservoir.
33. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the lid includes a pneumatic pressure port for
the waste reservoir.
34. The integrated structure for microfluidic analysis and sorting
of claim 33 wherein the lid further includes a pneumatic pressure
port for the target collection reservoir.
35. The integrated structure for microfluidic analysis and sorting
of claim 32 wherein the lid includes a pneumatic pressure port for
the waste reservoir.
36. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the lid provides optical access to the
reservoirs.
37. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the lid includes snap-on attachments to couple
to the cartridge.
38. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the filter is gas permeable.
39. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the filter is fluid impermeable.
40. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the filter is a polypropylene filter.
41. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein curable adhesive is disposed between the chip
and the cartridge.
42. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein the adhesive is UV curable.
43. The integrated structure for microfluidic analysis and sorting
of claim 25 further including a bonding sheet between the chip and
the cartridge.
44. (canceled)
45. The integrated structure for microfluidic analysis and sorting
of claim 25 wherein optical access to the chip is provided through
he optical window and through the reverse side of the chip.
46-51. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
11/781,848, filed Jul. 23, 2007, which claims priority to U.S.
Provisional Patent Application No. 60/925,563 filed on Apr. 20,
2007, the contents of which are incorporated by reference herein in
their entirety as if fully set forth herein.
FIELD OF THE INVENTION
[0002] This invention relates to methods and apparatus for the use
of forces in a microfluidic channel network to provide a switch
that enables selective routing of target cells through the network
to sort them from non-target cells and collect them. Of particular
interest are optical or fluidic switching forces.
BACKGROUND OF THE INVENTION
[0003] Conventional fluorescent activated cell sorters (FACS) are
widely used in research and clinical applications.sup.1. These
instruments are capable of very fast, multiparameter analysis and
sorting but generally require large sample volumes, a trained
operator for operation and maintenance, and are difficult to
sterilize. FACS instruments are able to analyze as few as 10,000
and as many as tens of millions of cells. However, below 100,000
cells the ability to perform sorting diminishes.sup.1. Other
separation methods such as magnetic beads don't require as many
cells as FACS but they suffer from nonspecific binding, aggregation
of cells and beads, and from the possibility that the beads
themselves could interfere in subsequent processing steps. Thus,
for sorting precious, small samples or cells from primary tissue, a
cell sorter that is capable of handling small sample volumes with
low cell numbers and that allows efficient recovery of the sorted
populations addresses a unique scientific niche.
[0004] Microfabricated cytometers have the potential to sort with
as few as 1,000 cells while concomitantly consuming less reagents
in an easy to use, closed system. The latter is important because,
unlike conventional FACS instruments, aerosols are not created,
reducing the risks of contamination of the sorted cells and of
working with biohazardous materials. Several microfabricated cell
sorters have been described, but mostly as "proof of concept". Fu,
et al..sup.2 reported 30-fold enrichment of E. coli at a throughput
of 17 cells/s. Only 20% of the bacteria were viable after sorting
and the sort purity in the target reservoir was 30%. In a
subsequent study.sup.3, the throughput increased to 44 cells/s but
the target purity decreased to less than 10%, with recovery
reported as 39%. Wolff, et al..sup.4 were able to sort beads from
chicken red blood cells at a throughput of 12,000 events/s, with
100-fold enrichment. However, purity in the target well was about
1%. In these studies, enrichment was defined as the increase in the
concentration of the target population in the collection well
compared to the starting concentration. Purity referred to the
accuracy of the sort and was the percentage of target cells sorted
over all cells sorted into the collection well. Recovery was
defined as the number of cells counted by the fluorescent detector
vs. cells recovered from the collection well. The latter two
studies used pressure switches in microfluidic devices that
switched the entire fluid flow path and, consequently, any
particles contained within the fluid plug. The mechanical
compliance in these switches caused the fluid switch speed to be
the rate limiting step for throughput.sup.3. Electrokinetic flow
control has also been reported, e.g., electroosmosis.sup.2,5,6 or
dielectrophoresis.sup.7,8,9, but the high electric field gradients
and physicochemical restrictions on the ionic strength of the
buffer are non-ideal conditions for cells.
[0005] Buican et al..sup.9 first proposed the use of optical forces
for the deflection of particles through a fluidic channel. The
force exerted on a particle by an optical beam is a function of the
optical power and the relative optical properties of the particle
and its surrounding fluid medium. Forces on the order of 1 pN/mW
can he achieved for biological cells approximately 10 .mu.m in
diameter. While the optical force is small, the force necessary to
deflect a cell into an adjacent flowstream is also small, e.g. 900
pN to move a 10 .mu.m. diameter cell, 20-40 .mu.m laterally across
the flow in a few milliseconds. This is the force necessary to
overcome the viscous drag force On the cell at the velocity implied
by this lateral motion.
[0006] The principles behind the optical forces and general
background technology may be found in U.S. Pat. No. 6,744,038,
which is incorporated herein by reference as if fully set forth
herein.
[0007] Various pneumatic pressure modulation systems and methods
for particle sorting in microfluidic devices have been known to the
prior art. By alternating pneumatic pressure interfacing to a
microfluidic device, particles including cells flowing in the
microfluidic channel can he directed to desired branch or branches,
so that a low cost sorting functionality can be achieved.
SUMMARY OF THE INVENTION
[0008] As described below, these forces are used to realize a
switch in a microfluidic channel network, operable as a cell
sorting system. The switch is triggered by detection of a
fluorescence signal from target cells flowing in the microfluidic
channel network upstream of the switch position, although other
detection modalities such as light scattering could equally be used
for activation of the switch. The switch is used to direct cells or
particles into one of a multiple number of output channel flow
streams without modifying the underlying flow, whereby the desired
cells are collected for further use. It is desirable that the flow
in a microfluidic channel is typically laminar at a very low
Reynolds number. Consequently, any cell flowing in a particular
lamina, or flow stream, will stay in that flow stream in the
absence of any forces transverse to the lamina. The switch utilizes
forces on a cell to accomplish just this, the transport of cells
transverse to the lamina to move the cells from a flow stream that
exits a bifurcation junction through one output channel to a flow
stream that exits the bifurcation junction through the second
output channel.
[0009] In one embodiment, a cell sorter comprises a cell inlet
adapted to receive one or more cells in a fluidic medium; a first
and second buffer inlets fluidically coupled to the cell inlet to
provide buffer solution to the sorter, a fluidic channel
fluidically coupled to the cell inlet and first and second buffer
inlets, a first lateral flow channel fluidically coupled to the
fluidic channel, first and second outputs fluidically coupled to
the fluidic channel, the outputs being located downstream of the
lateral flow channel, a detector adapted to detect cells of a given
state and to generate a signal in response thereto, the detector
positioned to detect cells at a position upstream of the first
lateral flow channel, a lateral force switch coupled to the
detector and actuatable in response to the signal to cause fluid to
move within the lateral flow channel; whereby when a cell of a
given state is detected, the lateral force switch is activated to
provide a lateral force on the cell so as to move the cell such
that it selectively exits into the first or second outputs.
[0010] The invention described in the following paragraphs details
the methodology used to create a switch and the approaches used to
optimize the switch, the design of the microfluidic channel network
and the properties of the flow of cells or particles in the
microfluidic network in order to achieve enhanced sorting
performance. In the event of an optical switch, the optical switch
generally works by projecting an optical illumination field into
the microfluidic channel network in the vicinity of the cell's
trajectory in an established flow in a microfluidic channel. The
interaction of the cell with the optical field produce forces on
the cell that transport it transverse to the established flow such
that it moves from one flowstream to another flowstream in the
established flow, without trapping the cell or significantly
altering its motion in the primary flow.
[0011] In the following text the terms cells and particles both
will be understood to mean any of biological cells, biological
particles, natural organic or inorganic particles and man-made
organic or inorganic particles. The size range of the cells sorted
in the microfluidic channel network is typically that of biological
cells, with diameters ranging from approximately 1 .mu.m to
approximately 50 .mu.m. More generally, cells with diameters
ranging from approximately 100 nm to approximately 100 .mu.m are
candidates for sorting by means of a switch in a microfluidic
channel network.
[0012] In one embodiment, an optical switch is utilized. In general
a laser has been used to produce the optical beam used in the
optical switch. The laser currently used for the optical switch is
a near-IR, continuous wave laser that is known not to harm the
viability of biological cells at the power densities and exposure
times used to demonstrate optical switching. Alternate laser
sources may be considered for different applications, including
visible or near-UV wavelength lasers if damage to the particles is
not an issue, or pulsed lasers where a large flux of light can be
used to move the particle very quickly. However, the source of the
optical beam does not need to be limited to a laser, even though
further discussion of the invention uses a laser to produce the
optical switch.
[0013] In yet another embodiment, a fluidic switch may be utilized.
Preferably, a pneumatic based fluidic switch may be utilized. In
another embodiment, a microfluidic chip design for cell sorter uses
pneumatic pressure modulation. A single side channel for flow
switching or cell sorting may be used in microfluidic devices. The
described channel geometry provides for efficient pneumatic flow
switching in microfluidic devices. In yet another aspect, a
coupling of two switching valves on a single side channel minimizes
pneumatic switching response time. In yet another aspect, a
cartridge holder is provided for pneumatic control of microfluidic
chips.
[0014] With particular application to a fluid switching system, a
fluidic sorter switching system comprises an inlet adapted to
receive a fluidic medium; a fluidic channel fluidically coupled to
the inlet, first and second lateral flow channels fluidically
coupled to the fluidic channel, first and second pneumatic valves
connected to the first and second lateral flow channels, first and
second outputs fluidically coupled to the fluidic channel, the
outputs being located downstream of the lateral flow channel, and a
control system, the control system being coupled to the first and
second valves, the control system providing timed control signals
to actuate the first and second pneumatic valves, characterized in
that the first valve is opened prior to the second valve being
opened. In yet another aspect, the switch is further characterized
in that the first valve is closed after the second valve is opened
and prior to the second valve closing. In yet another aspect, the
second lateral flow channel and second pneumatic valve may be
eliminated to achieve soiling using a single lateral channel with
one or two pneumatic valves.
[0015] In yet another embodiment, a microfluidic cell sorter uses
both optical switch and pneumatic pressure modulation. An optical
and opto-mechanical design is also provided. Preferably two laser
illumination modules and dark illumination module are utilized.
High performance high NA (numeric aperture) objective lens are
preferably used to collect fluorescence.
[0016] In yet other aspects of the inventions, fluorescence signal
detection and processing systems and methods are utilized. An ADC
is preferably used to convert the analog signal to digital signal.
In one embodiment, digital signal processing algorithm is
implemented in a FPGA.
[0017] Optionally, auto alignment of the cartridge is provided.
This invention solves the auto alignment problem for cartridge
loading in the system.
[0018] In yet other aspects, the inventions relate to the
application software design for the microfluidic sorter instrument.
Streaming raw data from external device between multiple executable
applications and processes in a format that is recordable,
lossless, and high speed (10 Mega-Bits-Per-Second or greater).
[0019] In yet other embodiments, a microfluidic cartridge priming
station is provided. The invention describes of priming station for
priming of microfluidic devices.
[0020] In yet other aspects, dilution cloning for growth monitoring
and selection of cells, e.g., fetal cells, is provided. The
invention describes dilution cloning method for growth monitoring
and selection of such cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a plan view of a "Y" shaped sorting junction in a
microfluidic channel network.
[0022] FIG. 2 is a plan view of a microfluidic channel network that
incorporates both a sheath flow pinch junction and a "Y" shaped
sorting junction connected by a main channel, with 50/50 splitting
of cells in the flow, collectively referred to as a 50/50 optical
switch network.
[0023] FIGS. 3a and 3b are plan views of a microfluidic channel
network that incorporates both a sheath flow pinch junction and a
"Y" shaped sorting junction connected by a main channel, with
skewed splitting of cells in the flow via differential sheath flow,
collectively referred to as a sheath flow skewed optical switch
network, with an optical switch.
[0024] FIGS. 4a and 4b are plan views of a .microfluidic channel
network that incorporates both a sheath flow pinch junction and a
"Y" shaped sorting junction connected by a main channel, with
skewed splitting of cells in the flow via differential outlet
channel width, collectively referred to as an outlet flow skewed
optical switch network, with an optical switch.
[0025] FIG. 5 is a 50/50 optical switch network with a
bi-directional laser line optical switch.
[0026] FIG. 6 is a 50/50 optical switch network with a
bi-directional laser spot optical switch.
[0027] FIGS. 7a, 7b and 7c are plan views of laser line optical
switches in larger microfluidic channel networks with more than two
outlet channels.
[0028] FIGS. 8a, 8b and 8c show optical designs for modulation
and/or shuttering of the optical switch.
[0029] FIGS. 9a and 9b are plan views of a sheath flow skewed
optical switch network with a laser spot optical switch that is
translated parallel to the cell flow or at an angle to the cell
flow.
[0030] FIGS. 10a, 10b, 10c and 10d show a detector arrangement and
timing/trigger diagram using a single laser source for the cell
detection and trigger decision method.
[0031] FIGS. 11a, 11b, 11c and 11d show a detector arrangement and
timing/trigger diagram using two laser sources for the cell
detection and trigger decision method.
[0032] FIG. 12 is a schematic of a representative design for
photolithography masks for microfluidic channel networks in both
bottom and top glass substrates that provides a 2-dimensional
sheath flow pinch of the cell flow in the main channel when these
substrates are bonded to form a single network.
[0033] FIG. 13 shows a 3-dimensional illustration of the design
described in FIG. 12.
[0034] FIG. 14 is an illustration of the side view of a
microfluidic channel network that provides sequential sheath flow
pinch of the cell flow in the vertical direction and then in the
horizontal direction, resulting in full 2-dimensional sheath flow
pinch of the cell flow in the main channel.
[0035] FIG. 15 is a 3-dimensional illustration of the microfluidic
channel network described in FIG. 14.
[0036] FIG. 16 is a schematic of a representative photolithography
mask design for both bottom and top glass substrates that when
bonded together form the microfluidic channel network illustrated
in FIGS. 14 and 15.
[0037] FIG. 17 is a representative embodiment of a photolithography
mask for a complete microfluidic channel network, with a T-pinch
junction and a T-bifurcation junction to the outlet channels, to
implement the optical switch based cell sort method.
[0038] FIG. 18 is a representative embodiment of a photolithography
mask for a complete microfluidic channel network, with a
triangle-pinch junction and a Y-bifurcation junction to the outlet
channels, to implement the optical switch based cell sort
method.
[0039] FIG. 19 shows a preferred embodiment of a microfluidic
channel network in a completed microfluidic cell sorting chip.
[0040] FIG. 20 shows a preferred embodiment for a self-contained
disposable cartridge for the optical switch based microfluidic
channel network cell sorter.
[0041] FIG. 21 shows a preferred embodiment of the optical system
for the optical switch based microfluidic channel network cell
sorter.
[0042] FIG. 22 shows representative performance of the optical
switch based microfluidic channel network cell sorter for various
implementations of the optical switch.
[0043] FIG. 23 is a plan view of a prior art "Y" shaped sorting
junction in a microfluidic channel network that shows a particle
trajectory for pneumatic based fluidic switching
[0044] FIGS. 24a and 24b are plan views of a "Y" shaped sorting
junction in a microfluidic channel with a two-channel fluid switch
that shows possible particle trajectories under various pneumatic
differential pressures.
[0045] FIGS. 25a and 25b are plan views of a "Y" shaped sorting
junction in a microfluidic channel with a one-channel fluid switch
that shows possible particle trajectories under various pneumatic
differential pressures.
[0046] FIG. 26 shows a preferred embodiment of a Y'' shaped sorting
junction in a microfluidic channel with a one-channel fluid
switch.
[0047] FIG. 27 shows a coupling of two switching valves to minimize
pneumatic switching response time and control the pneumatic profile
in a one-channel fluid switch.
[0048] FIGS. 28a and 28b show a coupling of two switching valves
and graphs of flow current across channel as a function of time to
minimize pneumatic switching response time and control the
pneumatic profile in a two-channel fluid switch.
[0049] FIG. 29 is a cartridge holder for pneumatic control of
microfluidic chips.
[0050] FIG. 30 shows a measurement of fluorescent calibration beads
performed on the instrument described herein.
[0051] FIG. 31a shows a fluorescence microscope image of
DAP1-stained Jurkat cells and FIG. 31b shows a fluorescence
microscope image of target Jurkat cells with CellTracker Green.
[0052] FIG. 32 shows a microfluidic cartridge priming station. The
invention describes of priming station for priming of microfluidic
devices.
[0053] FIG. 33 shows dilution cloning for growth monitoring and
selection of fetal cells. The invention describes dilution cloning
method for growth monitoring and selection of fetal cells.
[0054] FIG. 34 is a shallow microfluidic channel for
one-dimensional flow focusing. The invention describes a method to
overcome intrinsic velocity dispersion of one-dimensional flow
focusing for microfluidic flow cytometry or sorting.
[0055] FIG. 35 shows cell/particle detection inside multi-phase
microfluidic drops. The invention describes several detection
methods for cell/particle counting inside multi-phase microfluidic
drops.
[0056] FIG. 36 is a microfluidic outlet port configuration for
efficient sample collection. The invention describes several sample
collection methods after cell or particle sorting using
microfluidic devices.
[0057] FIG. 37 is a microfluidic device for multiple sample
analysis or sorting. The invention describes several microfluidic
devices for multiple sample analysis or sorting.
[0058] FIG. 38 is a microfluidic analysis chip for sample analysis
and recovery. The invention describes several microfluidic devices
for sample analysis and recovery with less dilution
DETAILED DESCRIPTION OF THE INVENTION
[0059] FIG. 1 shows one embodiment of an optical switch 10 that
serves to sort cells in a 1.times.2 microfluidic channel network,
i.e. a network with one main input channel 11 and two output
channels 12 and 13 extending from a bifurcation junction. A "Y"
geometry for the bifurcation junction is shown in FIG. 1, but other
bifurcations such as a "T" geometry may also be used. In general
these microfluidic channels are produced in optically transparent
substrates to enable projection of the optical switch and other
cell detection optics into the channel. This substrate is
typically, but not limited to, glass, quartz, plastics, e.g.,
polymethylmethacrylate (PMMA), etc., and other castable or workable
polymers (e.g. polydimethylsiloxane, PDMS or SU8). The depth of the
microfluidic channels is typically in, but not limited to, the
range 10 .mu.m to 100 .mu.m. The width of the microfluidic channels
is typically, but not limited to, 1 to 5 times the depth. The cross
section is typically rectangular, or rectangular with quarter-round
corners in the case of microfluidic channels produced by
photolithographic masking of glass substrate followed by isotropic
etching of the channels.
[0060] The flow conditions are set such that when the optical beam,
in this case from a laser, is turned off or blocked so that the
beam does not impinge on the junction region, all cells will
preferentially flow into one of the output channels, for example
the right output channel 13. When the optical beam is turned on or
unblocked, the beam strikes the junction region and optical forces
generated by the interaction of the cells with the optical beam
direct the cells into the left output channel 12. In this example,
the optical pattern chosen for directing the cells is a long, thin
line of laser illumination at some angle relative to the direction
of fluid flow. Optical gradient forces displace the cells
laterally, away from the main stream line of cells, such that
switched cells then exit the main channel into one output channel,
for example 12 while unswitched cells from the main stream of cells
exit into the other output channel, for example 13. The setting and
control of the flow conditions in the microfluidic channel network
can be achieved by direct drive pumping, pneumatic pumping,
electro-kinetics, capillary action, gravity, or other means to
generate fluidic flow.
[0061] The performance of the sorting mechanism in terms of
throughput (the temporal rate of cells entering the sorting region
at the top of the bifurcation junction), yield efficiency (the
fraction of target cells in the target output channel, 12), and
purity (the ratio of the number of target cells to the total number
of cells in the target output channel, 12), are impacted by various
factors, each of which affects the implementation of the optical
switch. The optical switch can be characterized by several
parameters such as the shape of the optical pattern projected into
the sorting junction region of the microfluidic channel network,
the position of the pattern with respect to the bifurcation
junction, any motion of the optical pattern with respect to its
initial position and shape, the duration of activation of the
optical switch, the wavelength and power of the laser source used
to produce the optical switch pattern, etc. The selection of
particular values of these parameters for the optical switch is a
critical function of, among other things, the topology and geometry
of the microfluidic channel system, the flow rates (cell
velocities) within the microchannel system, the ability to control
the position of cells flowing in the main channel (whether they are
flowing in the center of the main channel or off-set to one side),
the amount of displacement of the cells necessary to achieve
reliable switching, the depth of the channels, the shape of the
channels, and the forces produced by the cells' interactions with
the optical switch.
[0062] In general, when cells are introduced into the flow in the
main channel they may move down the channel at any transverse
position within the flow. Consequently the cells may be moving at
differing velocities, depending upon their transverse positions due
to the well known parabolic (for cylindrical microfluidic channels)
or quasi-parabolic (for more general cross sections) velocity
profile of pressure driven flow in microfluidic channels. This
would make it difficult to bias the flow of all cells to one output
channel, say 13, as shown in FIG. 1. Any implementation of an
optical switch with this flow geometry would necessarily result in
low throughput and inefficient use of the laser power available to
produce the optical switch. Any implementation of a fluidic switch
with this flow geometry would result in low throughput, purity and
yield due to the variable cell time of flight between the detection
region and the switching region. The use of appropriate flow
conditions can help alleviate these restrictions on the performance
of the optical or the fluidic switch.
[0063] Establishing the appropriate flow conditions can be done in
many ways. In one embodiment, 1-dimensional focusing of cells
(horizontally in the planar view shown) into a single file in the
center of the main channel is achieved by pinching the cell input
channel flow 20 with added flow of buffer from both the left 21 and
right 22 sides, using a sheath flow approach as shown in FIG. 2.
Maintaining the cells in the center of the main channel is achieved
by having equal flow from each side. This flow effectively creates
a fluidic splitting plane 23, as shown in FIG. 2, and this
ultimately will result in a 50/50 splitting of the fluid and cells
at the bifurcation junction. Implementation of an optical switch to
sort target cells from a mixed population of cells using this
microfluidic channel design and flow conditions requires an optical
switch that actively switches both target cells to one output
channel, say 12 as shown in FIG. 1 and non-target cells to the
other output channel, say 13. Implementation of a fluidic switch to
sort target cells from a mixed population of cells using this
microfluidic channel design and flow conditions requires an fluidic
switch that actively switches both target cells to one output
channel, say 12 as shown in FIG. 1 and non-target cells to the
other output channel, say 13. A two-channel fluidic switch in FIG.
24 is an example of such an embodiment.
[0064] Alternatively, the focused line of cells can he positioned
off-set from the center of the main channel by putting unequal
flows into the side sheath flow channels, FIG. 3a-b. This
effectively causes a skewed flow of cells from the input channel 30
to one side of the splitting plane 33 within the main channel. The
side of the main channel to which the cell flow is skewed will be
opposite to the side in which the sheath flow has the higher flow
rate. That is, when the right sheath buffer 32 flows faster than
the left sheath buffer 31, the line of cells is skewed toward the
left of the flow in the main channel, as shown in FIG. 3a-b.
However, the left sheath flow could also have the higher flow which
would push the line of cells toward the right side of the main
channel. Also shown in FIG. 3a-b are a fluorescence detector 34 and
an optical switch 35. The fluorescence detector is used as a means
to decide which cells to sort, and will be discussed in further
detail later. It is evident from FIG. 3b that an effective sort
involves moving a cell across the splitting plane from a flow
stream that exits the bifurcation junction to the
fluorescence-negative non-target cell microfluidic channel 36 into
a flow stream that exits the bifurcation junction to the
fluorescence-positive, target cell microfluidic channel 37.
Manipulation of the sheath buffer flow rate can be achieved either
by separately controlling the flow rate in the respective side
channels using direct drive pumping, pneumatic pumping,
electro-kinetics, capillary action, gravity, or other means to
generate fluidic flow, or by specifically designing the
microfluidic sheath network to ensure that central flow (50/50
splitting) or off-set flow occurs, through careful balancing of the
pressure drops in each of the microfluidic channels.
[0065] An alternative approach to achieve the preferential flow of
all cells from the input flow 40 in the main channel into one
output microfluidic channel, say the fluorescence-negative channel
46, prior to fluorescence detection 44, is to obtain central
pinching using equal sheath buffer flow rates 41 and 42, but then
preferentially bias the cell flow into fluorescence-negative
channel by having a larger volumetric fluid flow out of the
bifurcation junction into the fluorescence-negative output channel
46 relative to the fluorescence-positive output channel 47. This is
demonstrated in FIG. 4a-b, in which the left output channel 46 is
wider than the right output channel 47. This configuration
effectively places the splitting plane 43 to the right of the
centrally located cell stream. Therefore, with the cells in the
desired position, the optical or fluidic switch 45 is then used to
translate the target cells across the splitting plane into the
target cell, fluorescence-positive, right output channel. This
approach is equally effective by having the right output channel
wider than the left output channel, whereby target cells are
translated by the optical or fluidic switch across the splitting
plane, which is now located to the left of the centrally located
cell stream, and are consequently sorted into the left output
channel. Thus, by specifically designing the microfluidic channel
outlet network, or by actively controlling the outlet back pressure
in the respective outlet channels, the flow of cells into a desired
output channel can be controlled.
[0066] The use of either central flow or an off-set flow, and the
respective distance of the focused cell flow from a fluidic
splitting plane, ultimately dictates the magnitude of the
displacement of the cells necessary to achieve reliable switching.
This further dictates the length of the laser line and the laser
power required to achieve reliable optical switching or the
amplitude and duration of the pneumatic pulses required to achieve
reliable fluidic switching. The closer the cell stream is to the
splitting plane, the shorter the displacement required, and the
more efficient the sorting process becomes. For enhanced purity of
the sorted population and for high throughput, the single switch,
either optical or fluidic, in a mono-directional arrangement
requires the sample stream be offset from the splitting plane. In
this manner the occurrence of a mistaken sort is minimized. For
samples heterogeneous in size, such as single cell suspensions of
primary tissues where cells and debris may vary in diameter from 1
.mu.m to 50 .mu.m, it is advantageous to favor a larger off-set at
the cost of throughput. For more homogeneous samples, e.g., cell
lines or polystyrene beads, a smaller off-set may be selected to
allow increased throughput.
[0067] An alternative to this design is to use a bi-directional
optical switch which utilizes two laser lines. With this approach
one laser line sorts the desired cells to one output channel, and
the other laser line sorts all other cells into the other output
channel. This approach can be used with either the 50/50, FIG. 2,
or the offset, FIGS. 3 and 4, splitting configuration. In the
latter case when a cell is not in the switching zone, one may
choose to leave the laser on in either of its two positional
states, or one may also shutter the laser during this time. The
optical switch can also be made bi-directional by having two
mirror-image laser lines impinging on the switching region, located
just above the bifurcation junction, which independently turn on to
direct cells to either of the two outputs stemming from the
bifurcation junction.
[0068] A schematic of the bi-directional optical switch using laser
lines in a. 1.times.2 microfluidic network is shown in FIG. 5. A
similar bi-directional optical switch has also be achieved with
laser spots directed to either side of the channel, as shown in
FIG. 6. As with the mono-directional optical switch, a single laser
source can be used in the bi-directional optical switch, or
alternatively the bi-directional optical switch can use two
independent laser sources. The bi-directional design potentially
offers some performance advantages versus the mono-directional
design. The first is that purity is potentially maximized because
every cell is directed by the laser. Secondly, the fluid flow is
simplified because equal flow can be directed out each of the two
output ports, instead of some predetermined ratio of flow.
[0069] Although only the 1.times.2 microfluidic channel design with
flow through one input main channel into a bifurcation to two
output channels has been considered thus far in this description,
microfluidic networks with 1.times.N, or M.times.N, outputs can be
utilized. Optical or fluidic switching can be achieved in these
larger networks by having an arbitrarily large number of
independently modulated laser lines or independent lateral flow
channels. Some embodiments are shown in FIG. 7a-c. Furthermore,
cells can also be fed back multiple times through the same sorter
to increase the purity of the sort, or alternatively, channels can
also be arranged in a cascade for multiple levels of sorting.
[0070] Two different activation modes cart be considered when
operating the optical switch in a mono-directional or
bi-directional arrangement; a passive mode or an active mode. The
passive mode is such that the state of the optical switch is either
on or off, regardless of what cell may be flowing through the
channel. In this case knowledge of when or how many cells are
entering the switching region is not required, and consequently,
depending on the state of the laser, all cells within the switching
region are switched. Alternatively, in the active mode the cells
are first detected as they enter a detection/selection region, and
then are switched based on some decision process. FIG. 3a-b and
FIG. 4a-b show examples of this mode that use a fluorescence
detector placed just prior to the switching region. In this case,
all fluorescent cells were directed to one output channel, and all
non-fluorescent cells were directed to the other output channel.
Other non-fluorescent detection/selection techniques for the
decision process include Time-Of-Flight, scatter, imaging,
capacitance, or any detection modality that can identify a desired
cell. Regardless of the detection/selection method, switching using
the active mode can be utilized to sort one population of cells
from another based on some decision process.
[0071] In order to utilize the active mode, the optical beam must
be modulated on or off in response to the decision process.
Regardless of the number of lasers used, or whether the optical
switch is mono-directional or bi-directional, the lasers can be
modulated in many ways, including using an electro-optic modulator,
modulating the laser power, shuttering the laser, using a liquid
crystal modulator, using a galvanometer, and using an acousto-optic
modulator. For the bi-directional optical switch with two lasers,
the separate lasers can be turned on and off independently;
however, when using a single laser source the two different
orientations of the optical switch line can be achieved by using a
polarization rotator (such as a liquid crystal modulator) and
having each of the two different line patterns be each of two
separate polarizations. Similarly, an acoustic-optic modulator or a
galvanometer mirror can he used to modulate the position of a
single spot used as the optical switch, or a two-axis acousto-optic
modulator or two-axis galvanometer mirror can be used to draw two
different line shapes to be used as the bi-directional optical
switch.
[0072] FIG. 8 shows three different possible optical designs for
performing the modulation and/or shuttering of the optical switch.
In FIG. 8a the bi-directional optical switch is created from a
single optical beam (laser) directed toward and passing through a
Liquid Crystal Modulator (LCM). The LCM is a polarization rotator
and therefore if the beam is polarized in one direction it will
pass straight through the Polarizing Beam Splitter (PBS), through a
cylindrical lens creating a line shape, through another PBS, and
then through some focusing optics which focus the line onto the
microfluidic switching region. This effectively creates one line of
the bi-directional optical switch used to switch cells into one of
the bifurcated channel outputs. To switch cells into the other
output channel a mirror image line must be created. This is
accomplished by rotating the LCM which alters the polarization of
the beam. Consequently, when the beam strikes the first PBS it is
directed into an alternate path through a different cylindrical
lens (creating a line shape), through the other PBS, which directs
the beam back through the focusing optics which focus the mirror
image line onto the microfluidic switching region. Note that the
cylindrical lenses were used to create the line shape for the
bi-directional optical switch; alternatively the cylindrical lenses
can he removed resulting in spots used for the optical switch. In
FIG. 8b, rather than use the combination of the LCM and PBS, with
or without the cylindrical lenses, an Acousto-Optic Modulator (AOM)
can he used to create the lines or spots used in the bi-directional
optical switch. This is achieved by configuring the AOM to obtain
the desired line shape that is required. Also, the AOM can he used
to shutter the optical beam in an on/off fashion, directing the
beam to a beam stop for the Optical Switch off condition. FIG. 8c
shows the combination of the systems described in FIG. 8a and FIG.
8b. In any configuration that uses an AOM to vary the direction of
the beam, a galvanometer mirror, either one-axis or two-axis,
depending on the desired beam motion, may be used in place of the
AOM.
[0073] Many variations for the optical pattern can he considered
when optimizing switching efficiency for mono- or bi-directional
optical switches. As mentioned above a laser line has been used as
the optical switch pattern. The line might be generated by a
cylindrical lens, by scanning a galvanometer mirror or an
acousto-optic modulator, by a diffractive optic, by a custom
refractive optic, or by any other technique. To date the line has
been generated using a cylindrical lens, by scanning a galvanometer
or by using an acousto-optic modulator. The length of the line can
be arbitrarily long or as short as a single point. The line can
have higher intensity at the top of the line and gradually taper
down in intensity toward the end of the line. Additionally the line
might be a curved arc which optimizes the output direction of the
cells. Additionally, in real time the angle of the line or the
shape of the line might vary (i.e. swivel to optimize output). For
implementations with multiple output channels, any arbitrary
pattern of lines in 2D space might be generated to optimize the
direction of each output cell. Alternatively, the line might he
created by an array of discrete spots.
[0074] To further improve the performance of the sorting mechanism
in terms of throughput, yield efficiency, and purity, the optical
switch has been configured such that the laser spot is swept
alongside a selected cell as it flows down the main channel toward
the bifurcation junction, thereby increasing the total interaction
time between the cell and the laser. The optical switch utilizes a
laser spot which is translated, in a straight line, down the length
of the main channel toward the bifurcation junction. The line swept
by the spot can be parallel with the walls of the main channel
(FIG. 9a), or can be at some angle relative to the cell flow stream
(FIG. 9b). Therefore, the angle can range from 0-90 degrees. The
ability to sweep the spot is achieved using either an AOM or
scanning galvanometer mirrors. The optical switch is triggered to
sweep by a decision based on detection of the desired cell using
fluorescence or other detection modality that can identify a
desired cell; for example Time-Of-Flight, scatter, imaging, or
capacitance. The cell position can be either off-set or centered in
the main channel, which dictates the length of the line swept by
the spot and the laser power used to achieve efficient
switching/sorting. Thus, as a desired cell is detected the optical
switch is turned on, and the spot appears alongside the desired
cell. The spot then tracks alongside the selected cell and uses
optical forces to direct the selected cell into the desired output
channel.
[0075] Two approaches to facilitate efficient triggering of the
optical or fluidic switch are described below. Typical to both
methods is the use of a temporal signal to analyze the moving cell,
and use this information to generate a decision to switch, or not
to switch. This temporal signal is essentially a measure of a
signal as a function of time, which can yield a distinctive
temporal fingerprint in terms of both peak intensity and peak
width. The signal may he fluorescence, scatter (for instance,
forward scatter), capacitance, imaging, or any detection modality
that can identify a desired cell. One approach is to utilize a
single laser source coupled with two or more detectors to
accomplish both cell detection and cell identification. FIG. 10a-d
show this approach using one laser source combined with a
fluorescence detector and a forward scatter detector. The temporal
signals from these detectors are used as the information for the
switch decision. The presence of a cell is verified by the forward
scatter signal and when this signal is coupled with a fluorescence
signal intensity which is within a predetermined range; this
"gating" information is then used to trigger the optical switch.
Note that only a single fluorescence detector is shown, however
multiple fluorescence detectors can be used for further refined
cell identification. In the case depicted the cell stream is
centrally located by using equal flow rate sheath buffers, with
output channels having different widths used to create a splitting
plane to the right of the cell stream. However, any configuration
used to manipulate the position of the cell stream and splitting
plane, as discussed above, can be used. Also, common to both
configurations is the presence of an error checking detector, which
verifies whether a cell has been switched or not. The detection in
this case can be based on fluorescence, scatter (for instance
forward scatter), capacitance, imaging, or any detection modality
that can identify a desired cell.
[0076] FIG. 10a-b show the detector arrangement and the
timing/trigger diagram for when the sort parameter is negative and
the optical or fluidic switch is not triggered. The cells enter the
main fluidic channel and are focused into a single file by sheath
buffer flowing from both sides. As a cell passes the through the
laser in the detection/selection region, both fluorescence and
forward scatter signals are detected simultaneously, or nearly
simultaneously. Although the presence of a cell is successfully
detected via the forward scatter signal (at time t.sub.1), the
fluorescence signal is below the gating level and the optical
switch is not triggered (at time t.sub.2). Thus, no error check
signal (at time t.sub.3) is obtained since no cell was switched.
Alternatively, FIG. 10c-d show the detector arrangement and the
timing/trigger diagram for when the sort parameter is positive and
the optical or fluidic switch is triggered. Here, as a cell passes
through the laser in the detection/selection region, both
fluorescence and forward scatter signals are again detected (at
time t.sub.1) simultaneously, or nearly simultaneously, but the
fluorescence signal is within the gating level and the optical or
fluidic switch is triggered (at time t.sub.2). An error check
signal (at time t.sub.3) is obtained since a cell was switched. In
this approach the trigger time (at time t.sub.2) is a preset value
(.DELTA.t) measured from the initial detection time (t.sub.1), and
this .DELTA.t value is determined by the speed of the cells and the
position of the optical switch relative to the detection/selection
region. This approach is satisfactory to achieve efficient sorting;
however as a means to further improve the triggering accuracy a
second approach is used.
[0077] FIG. 11a-d shows this second approach, in which two laser
sources are used instead of one. Also, as with the single laser
approach described above, the temporal signals from these detectors
are used as the information for the switch decision. One laser is
used in a detection zone to separately accomplish cell detection
prior to the identification/selection region. The detection in this
case can be based on fluorescence, scatter (for instance forward
scatter), capacitance, imaging, or any detection modality that can
identify a desired cell. The second laser is coupled with two or
more detectors and is used to accomplish cell detection and cell
identification. Again, identification in this case can be based on
fluorescence, scatter (for instance forward scatter), capacitance,
imaging, or any detection modality that can identify a desired
cell. The purpose for two sequential cell detection steps is such
that the cell flow rate can be obtained from the time difference
(.DELTA.t) between the first detection (at time t.sub.1) and the
second detection (at time t.sub.2). Knowing the spacing between
detector windows (d) will yield the flow rate (v=d/.DELTA.t), and
this value combined with the known distance the optical or fluidic
switch is from the identification window (x) is then used to
calculate the triggering time for the optical switch (t.sub.3=x/v).
Again switching only occurs when specific gating levels are reached
for the cell identification step. Although only a single
fluorescence detector is shown for identification, multiple
fluorescence detectors can be used. In the case depicted the cell
stream is centrally located by using equal flow rate sheath
buffers, with output channels having different widths used to
create a splitting plane to the right of the cell stream. However,
any configuration used to manipulate the position of the cell
stream and splitting plane, as discussed above, can be used. Also,
common to both configurations is the presence of an error checking
detector, which verifies whether a cell has been switched or not.
The detection in this case can be based on fluorescence, scatter
(for instance forward scatter), capacitance, imaging, or any
detection modality that can identify a desired cell.
[0078] FIG. 11a-b shows the detector arrangement and the
timing/trigger diagram for when the sort parameter is negative and
the optical or fluidic switch is not triggered. The cells enter the
main fluidic channel and are focused into a single file by sheath
buffer flowing from both sides. The presence of a cell is verified
by the forward scatter signal (at time t.sub.1) as it passes
through the detection window region. As the cell passes through the
identification/selection window a second forward scatter signal is
obtained (at time t.sub.2), however, this signal is coupled with a
fluorescence signal intensity (at time t.sub.2) which is not within
the gating level and the optical or fluidic switch is not triggered
(at time t.sub.3). No error check signal (at time t.sub.4) is
obtained since no cell was switched. Even without sorting a cell
the flow rate (v) of the cell stream is obtained using (t.sub.1),
(t.sub.2) and the known distance (d) between the detection and
identification windows. This is obtained using the relationships:
.DELTA.t=(t.sub.2)-(t.sub.1) and v=d/.DELTA.t.
[0079] Alternatively, FIG. 11c-d show the detector arrangement and
the timing/trigger diagram for when the sort parameter is positive
and the optical or fluidic switch is triggered. Here, the presence
of a cell is again verified by the forward scatter signal (at time
t.sub.1) as it passes through the detection window region. As the
cell passes through the identification/selection window a second
forward scatter signal is obtained (at time t.sub.2), and this
signal is coupled with a fluorescence signal intensity (at time
t.sub.2) which is within the gating level and the optical or
fluidic switch is triggered (at time t.sub.3). An error check
signal (at time t.sub.4) is now obtained since a cell was switched.
In this approach the trigger time (t.sub.3) is not a preset value,
but rather it is calculated using the cell stream flow rate (v) and
the known distance (x) between the optical switch and the
identification window. This is obtained using the relationships:
.DELTA.t=(t.sub.2)-(t.sub.1); v=d/.DELTA.t; (t.sub.3)=x/v. This
approach allows for more efficient sorting as it can account for
fluctuations in cell flow rate, and therefore more accurately
trigger the optical or fluidic switch. An added benefit of this
approach for optical switching is, for each individual cell, the
possibility of adjusting the rate at which the laser spot is
translated down the channel such that it matches the velocity of
the cell as determined above, thus maximizing the interaction time
between the cell and the laser spot of the optical switch. The
translation velocity of the laser spot would be varied by varying
the driver for the AOM.
[0080] Another approach to improving the sorting efficiency, while
incorporating the triggering approaches described above, is to
centralize the cells in the main channel using channel designs
which create a true sample core, whereby the core is completely
surrounded by the sheath buffer. Variability in the location of a
cell along the channel height can cause variability in cell
detection and fluorescence intensity. Ensuring that the cells are
in a core flowing in the center of the main channel may improve
sorting efficiency, since this minimizes any variability due to
radial distribution of cells, and controls the distance the cell
needs to be moved to effect efficient sorting. Such a core flow can
be achieved with a 2-dimensional pinch of the input flow stream
with sheath buffer.
[0081] This approach requires a bottom substrate and a top
substrate; each with microfluidic channel networks formed in them.
FIG. 12a-b and FIG. 13 show one method to accomplish this, in which
the channel design on one substrate is the mirror image of the
design on the other substrate. Thus, when the two substrates are
brought together, with the channel designs facing each other, the
channel networks overlay and form complete fluidic conduits. FIG.
12a-b show one type of design used in this approach, with the
sample channel shown as a dashed line. The key feature of this
approach is to ensure that the sample channels are shallower than
the sheath channels, such that when the substrates are brought
together the sample conduit appears to enter the junction as a
hole. This is shown in FIG. 13, where the cells can be seen to
enter the junction, and then are pinched from all sides creating a
sample core which flows in the center of the main channel. Note
that the channels can be formed by wet chemical etch or laser etch
of glass or quartz, by molding or embossing in plastics or
polymers.
[0082] Another method involves having a series of intersecting
channels arranged such that in the first junction/intersection the
cells are pushed vertically toward one wall of the main channel,
the next junction/intersection forces this cell stream vertically
into the center of the main channel, and then a final pinch flow
from both sides at a third junction/intersection creates the
complete sheath buffer shroud around a sample core flowing in the
main channel. This is shown in FIG. 14 and FIG. 15, with one
possible channel schematic shown in FIG. 16. In this example, at
junction (A) sample flows from the top substrate into the junction
and down into the channel in the bottom substrate, where the side
sheath buffer flows into the junction from the sides. The sample is
slightly focused and pushed to the top wall of the bottom channel
as it continues to flow toward the next junction (B). At junction
(B) the sample flows along the top of the bottom channel from
junction A to junction (B). Here a second sheath buffer flows into
the junction (B) from the top substrate and the sample is pushed
down to the middle of the channel in the bottom substrate. The
sample continues to flow along the middle of the bottom channel
toward the next junction (C). Here a third sheath buffer flows into
junction (C) from both sides, and the sample is pinched into single
file. The sample is now surrounded by sheath buffer as it continues
to flow, as a sample core, centered both horizontally and
vertically within the main input channel.
[0083] Another method uses a shallow channel in the axis orthogonal
to the 1-D sheath buffer to minimize the effects of a parabolic
velocity dispersion. In one-dimensional flow focusing in
microfluidic channels, particles or cells in the inlet center
stream are pinched along only one direction. In the direction
perpendicular to the pinch and the direction of flow, a parabolic
velocity profile remains. Particles near the center of channel flow
fast while ones close to channel wall flow slow. As a result,
particles or cells travel down the flow channel with a distribution
of velocities, which complicates synchronization of detection and
switching events. FIG. 34 shows a method to overcome the intrinsic
problem in 1-D microfluidic flow focusing, but using a channel
depth comparable to size of particles or cells in the orthogonal
direction. For example particles or cells with a diameter of 10
micrometer, channel depth can be 15 micrometer. In this case, the
particles or cells occupy most the channel in the depth direction,
so that they experience a velocity that averages out the velocity
distribution and narrows the velocity dispersion in the
channel.
[0084] All of the microfluidic channel network designs described in
FIGS. 1-16 have been produced in glass substrate utilizing
conventional photolithographic masking and isotropic etching of the
masked glass substrates. The isotropic etch typically produces
microfluidic channels that have a depth d.sub.e at the center of
the channel and a width w=w.sub.p+2.times.d.sub.e at the top of the
channel, where w.sub.p is the width of the photolithography pattern
that defines the channel. The bottom profile of the channel has a
quarter-round contour of radius d.sub.e at each edge due to the
isotropic etch and the top of the etched channel is open. A glass
substrate, typically a glass cover slip, is thermally bonded to the
substrate with the etched microfluidic channels to seal the tops of
the channels and complete a microfluidic channel network. Holes are
typically drilled in the top substrate prior to the thermal bonding
to provide vias for ingress and egress of fluid flow to the
microfluidic channel network, but alternately, holes also could be
drilled into the etched bottom substrate rather than the top
substrate. The depth d.sub.e of the channels depends on the rate of
the chemical etch process and the duration of the etch step. The
depth of the microfluidic channels is typically in, but not limited
to, the range 10 .mu.m to 100 .mu.m. The width of the microfluidic
channels is typically, but not limited to, 2 to 5 times the depth.
This is achieved by using lines on the photolithography mask that
are typically, but not limited to, the range 5 .mu.m to 400 .mu.m.
As mentioned previously, other substrates may be used, such as
plastics or moldable or castable polymers. In these cases, the
microfluidic channels typically have rectangular cross sections,
but otherwise are similar to the channels in the glass substrates.
The size of the glass substrate in which the microfluidic channel
network is produced is typically in, but not limited to, the range
of 5 mm.times.5 mm to 25 mm.times.50 mm with a total thickness in,
but not limited to, the range 500 .mu.m to 2 mm. The top substrate
is typically the same size, with thickness in, but not limited to,
the range 300 .mu.m to 1 mm. The vias are typically, but not
limited to, 200 .mu.m to 600 .mu.m in diameter. The completed
substrate, with a microfluidic channel network and a bonded cover
plate with vias for fluidic ports for ingress and egress of fluid
flow, is termed a microfluidic sorting chip or chip for
brevity.
[0085] The microfluidic channels networks shown in FIGS. 1-16
typically have only described the local geometries of the inlet
microfluidic channel, the sheath buffer pinch junction channels,
the cell identification and optical switch main channel, and the
bifurcation of the main channel to the outlet channel. This
description needs to be expanded to provide for regions in each
channel to make the connections to reservoirs in a macro-scale
fluidic device or cartridge that provides the interface to the vias
described above to provide ingress and egress of the fluid flow
from the network. The cross section and length of each of these
microfluidic channels typically needs to be adjusted to assure
appropriate controlled flow within the entire microfluidic channel
network, depending on the technique selected to achieve the flow in
the channels. Both the cross section and the length of these
channels are determined by the pattern used to produce the
photolithography mask.
[0086] FIG. 17 shows one embodiment of a mask for a complete
microfluidic channel network that has an inlet channel, two sheath
channels to a T-pinch junction and two outlet channels from a
T-bifurcation junction. This mask was designed to provide a 7:1
volumetric pinch ratio (the sheath flow rate is seven times greater
than the cell inlet flow rate). The length of the channels was
designed to provide both sufficient pressure drop to enable the use
of either standard low flow syringe pumps or low pressure pneumatic
controllers to establish the flow. The design also reflects the
balance of pressures needed to enable use of only two pumps, one
for the cell inlet channel and one for the two sheath channels,
with the outlets maintained at atmospheric pressure. The sheath
channel inlet is at the termination at the top of the design, the
cell inlet channel originates below this in the center of the two
sheath channels and is long enough to provide the appropriate
pressure drop to set the 7:1 pinch ratio, and the two outlets are
located at the termini at the bottom left and right.
[0087] FIG. 18 shows another embodiment that incorporates a
triangular junction for the pinch junction and a Y-bifurcation
junction, in a design that provides a 10:1 volumetric pinch ratio.
Otherwise the design is geometrically similar to that of FIG. 17.
Many other designs are clearly possible, but they all share the
common features of needing to provide for fluidic ingress and
egress and to provide appropriate pressure drops and pressure
balances for the method chosen to establish the fluid flow. Similar
design conditions are used to produce the photolithography masks
used to make the microfluidic channel networks for 2-dimensional
pinch flow networks described previously.
[0088] FIG. 19 shows a preferred embodiment of a microfluidic
channel network in a completed microfluidic sorting chip. The two
inlet ports, for the cell sample flow and for the sheath buffer
flow are identified, as are the two outlet ports, for the
fluorescence-positive target cells and for the
fluorescence-negative non-target cells, the waste stream. The chip
is 24 mm by 40 mm. The thickness of the etched substrate is 1.1 mm.
The thickness of the bonded cover plate is 550 .mu.m. The
microfluidic channels are 50 .mu.m deep. The cell inlet
microfluidic channel is 110 .mu.m wide. The sheath flow and outlet
microfluidic channels are 150 .mu.m wide, as is the main
microfluidic channel. The sheath flow pinch junction is an inverted
equilateral triangle, 300 .mu.m per side, connecting the cell inlet
channel through the base of the triangle, at the top of the
junction, with the two sheath flow pinch channels from each side to
the main channel through the apex of the triangle, at the bottom of
the junction. This microfluidic channel network design is optimized
to use pneumatic control of the flow at all four ports to establish
the network flow.
[0089] Microfluidic connections to the chip may be made in a
variety of ways. One method is to use flexible microfluidic tubing
directly connected to the ports, either by gluing or using various
tubing adapters that can be attached to the surface of the chip at
the ports. This tubing can be connected directly to syringe pumps
or similar systems that provide volumes for handling both the cell
sample and the sheath buffers and provide the pressure to flow
these volumes through the chip. Using the syringe pumps for
handling the sample volume requires that the pump be cleaned and
reloaded for each sample and introduces the possibility for carry
over or contamination from one sample to the next.
[0090] An improved method for microfluidic connections to the chip
utilizes a cartridge that is directly adhered to the chip using a
UV-curable adhesive, a PSA (pressure sensitive adhesive) bonding
sheet, or other conventional bonding methods, such as thermal
bonding. The cartridge has four built-in reservoirs that separately
provide interface connections to the cell inlet channel, the two
sheath channels (from one reservoir), and each of the two outlet
channels. Such a cartridge provides the possibility of sterile
handling of both the cell sample and the sorted target cells and
waste stream, since they can be completely confined to the volumes
of the cartridge before and after the cell sort. The flow for such
a cartridge and chip system can be provided by using two pneumatic
pressure controllers that separately pressurize the cell inlet and
sheath buffer reservoirs to induce flow through the microfluidic
channel network of the chip to the outlet reservoirs that are at
atmospheric pressure.
[0091] An improved flow control method is provided by using four
pneumatic controllers that separately pressurize each of the cell
inlet, sheath buffer, target cell collection and waste collection
reservoirs. Such a flow control system provides the ability to
separately adjust the volumetric pinch ratio at the sheath pinch
junction, the flow velocity of the cells in the main microfluidic
channel for the fluorescence analysis and optical switch, and the
split ratio at the switching bifurcation to enable biased flow, as
described previously.
[0092] FIG. 20 shows a preferred embodiment of a self-contained
disposable cartridge that provides fluidic reservoirs for the cell
sample volume, the sheath buffer volume and the two outlet
collection volumes for target cells and waste respectively. The
cartridge is manufactured from acrylic plastic and may either be
machined or cast. Other plastics or suitable materials may be
substituted for acrylic if appropriate. The cell sample volume is
typically conical in shape, tapering towards the port to the inlet
microfluidic channel. In the preferred embodiment, the inlet
reservoir contains a polypropylene insert to minimize cell adhesion
and consequently maximize cell yield. The chip is bonded with UV
adhesive to the optical window region, and the outlet ports from
the chip interface with their respective reservoir volumes. The
reservoir volumes are sealed with the snap-on lid that has drilled
ports for connection between the pneumatic controllers and the
individual reservoirs. The lid contains a silicone gasket to aid in
sealing against the cartridge body. It also incorporates a 0.1
.mu.m polypropylene filter to create a gas permeable, liquid tight
interface between the cartridge volumes and the external
environment. This maintains aseptic conditions on the cartridge and
minimizes any biohazard contamination to the user or the
instrument.
[0093] The cartridge is prepared for a cell sorting run by first
priming the microfluidic channel network through the sheath port
with sheath buffer solution, using an ordinary syringe with a luer
fitting. In this way the channels are primed and the sheath
reservoir is filled with 800 .mu.l and each outlet reservoir is
filled with 200 .mu.l. The cell sample reservoir is aspirated of
excess buffer liquid and then 5-25 .mu.l of cell sample is placed
into the sample input reservoir using a pipette. The cartridge lid
is then applied and snapped into place, providing a self-contained
system in which to perform the cell sorting run.
[0094] The cartridge is designed to be placed in a holder that
positions the main channel of the chip such that the optical
imaging system that projects the optical switch beam into the
channel is appropriately aligned and focused into the channel. The
cartridge holder also includes a pressure manifold plate that has
four to six ports, connected by external tubing to the four
pneumatic controllers. Each manifold port is sealed to its
respective cartridge lid port with an o-ring, and these seals are
made leak free by pressing the manifold against the cartridge lid
with a cam-lock mechanism. FIG. 29 shows a preferred embodiment for
a cartridge holder for fluidic switching that integrates two
pneumatic valves on the manifold in order to shorten the volume and
path length of the pneumatic pulse. The manifold coupling pneumatic
pressure from a source to the pneumatic pressure port is done
without intervening tubing. This allows faster switching speeds for
higher performance and supplements the performance gain from the
switch configurations shown in FIGS. 27-28.
[0095] A preferred embodiment of the optical system for the optical
switch is shown in FIG. 21. The cartridge, with the pneumatic
manifold connecting to the snap-on lid, is positioned such that the
optical switch region is at the focus of both a lens system viewing
from above the cartridge and a lens system viewing from below. The
output beam from a 488 nm laser is projected through the imaging
system into the main channel just upstream of the sorting region,
as shown in FIGS. 3-7 and 9-11, to provide excitation for the
detection of fluorescence from fluorescence-positive target cells.
The fluorescence emission is collected by the same lens and imaged
through a dichroic mirror and an appropriate fluorescence emission
filter to a photomultiplier tube. The signal from the
photomultiplier tube is processed by the electronics to measure the
level of the fluorescence from the cells and determine the presence
of fluorescence-positive target cells in the flow stream in the
main channel. The fluorescence excitation is not limited to the 488
nm wavelength, but can be at any wavelength that is appropriate for
the fluorophores used to identify the target cells. If a different
excitation illumination is used, the wavelength of the fluorescence
emission filter must be changed accordingly. When
fluorescence-positive cells are identified, the electronics
triggers the AOM to direct the beam from the IR-laser, typically a
1070 nm laser operation between 5 W and 20 W output power, into the
main channel at the optical switch position. In the preferred
embodiment, the AOM is controlled to produce an optical switch
pattern as described in FIG. 9b, although any of the optical switch
methods previously described could be implemented. The lens below
the cartridge images the 488 nm excitation illumination onto a
photodiode. The signal detected by this photodiode is used to help
distinguish fluorescently labeled cells from smaller debris that
may carry the fluorescent label, and also to identify clumps of
cells that might have formed. These events are rejected as
candidates for sorting to the target output channel.
[0096] Yet another preferred embodiment would incorporate
appropriate imaging and optical filtering to provide a forward
scattering signal based on the illumination of the cell by the 488
nm laser that is used to excite the fluorescence. The optics would
provide a range of angular sensitivity, such as, but not limited to
this range, 0.8.degree. to 10.degree., for the detection of the
forward scattering signal. This signal can help characterize cells
in addition to the fluorescence signal, as well as help distinguish
cells from debris. The forward scattering illumination is not
limited to the fluorescence excitation laser, but could be at any
other wavelength provided by an additional light source that is
properly imaged into the main channel.
[0097] Yet another preferred embodiment would incorporate
additional fluorescence detection channels that are sensitive to
fluorescence emissions at different wavelength, typically using a
single excitation wavelength, such as, but not limited to, 488 nm.
Each detection channel would incorporate a PMT with an appropriate
dichroic mirror and emission filter for the fluorescence emission
wavelength of the additional fluorophore. From two to four
fluorescence detection channels are readily accommodated in this
manner. Using more than one fluorophore in this manner provides the
ability for multiple detection criteria to identify the target
cells for sorting with the optical switch.
[0098] Yet another preferred embodiment would incorporate an error
checking capability that provides optical illumination, typically
as a narrow line across one of the channels in the network, and
typically at a longer wavelength, perhaps, but not limited to, 785
nm from a solid state laser, that is outside the range of
wavelengths used for fluorescence detection and forward scatter
detection, but is shorter than the optical switch wavelength that
is typically at 1070 nm. This source can he appropriately imaged
into the microfluidic channel network to provide lines that can be
used to detect passage of particles through any vertical plane in
the network. This provides additional ability to check the
performance of the optical switch performance and provides
additional capability for the timing of the trigger of the optical
switch, as described in FIG. 11.
[0099] Yet another preferred embodiment of the optical system would
incorporate an additional optical illumination path at, but not
restricted to, 750 nm, e.g., as produced by band pass filtering the
light from an LED, and illuminating a region of the microfluidic
channels with that light. That region would be imaged through a 750
nm pass filter onto a CCD camera to provide visualization of the
performance of the cells flowing in the microfluidic channel
network at the bifurcation junction and/or at the pinch junction.
The filters before the camera would be adequate to block any
shorter wavelength radiation associated with the excitation or
detection of fluorescence and with the forward/side scatter optics
and the error detection optics. The fitters would also block the
longer wavelength, 1070 nm light from the optical switch.
[0100] The preferred embodiment of the cartridge shown in FIG. 20
is designed to hold the microfluidic channel network in a
horizontal configuration, so that all of the channels and
inlet/outlet ports are at the same vertical level. This minimizes
the effects of gravity on the pressure drops through the
microfluidic channels, leading to more stable and controllable flow
in the network. However, gravity will still have an effect on the
cells in the flow, particularly as the cells pass from the cell
sample reservoir into the cell inlet microfluidic channel. Another
preferred embodiment of the sorter, to help control the effects of
gravity on settling of the cells in this reservoir and on their
settling in the relatively slower flow in the inlet microfluidic
channel before the cells flow speeds up at the pinch junction, is
to enhance the buoyancy of the cells, such that settling of the
cells is minimized. Increasing the buoyancy can be achieved by
using additives in the sample buffer. Examples of these rheological
control additives, particularly those that are either pseudoplastic
or shear thinning, or both, are xanthan gum, carageenan, sodium
carboxymethylcellulose, methylcellulose,
hydroxypropylmethylcellulose, hydroxyethylcellulose,
hydroxypropylcellulose, hydroxypropyl guar, Gum Arabic, Gum
Tragacanth, Alginate, polyacrylates, carbomer. Other additives
include Histopaque.TM., which is a mixture of polysucrose and
sodium diatrizoate, and Optiprep.TM., which is a 60% w/v solution
of iodixanol in water. The concentration of these additives used
depends on the density of the cell being sorted. For instance, in
the case of Optiprep.TM. the concentration can range from 5% to
40%. Finally, salinity of the sample buffer and addition of sucrose
can also be used to adjust the buoyancy of cells.
[0101] The buffers that are used for the cell sample volume and for
the sheath flow can he any buffers that are biologically compatible
with the cells that are being sorted, and are compatible with
optical illumination that is used both for the fluorescence
detection modality and for the optical switch, i.e., the buffer has
sufficiently low absorbance at the fluorescence
excitation/detection wavelengths and the optical switch wavelength.
A preferred embodiment of the sheath buffer uses PBS/BSA, phosphate
buffered saline (PBS) at pH 7.2 with 1% bovine serum albumin (BSA)
fraction 5. A preferred embodiment of the cell buffer uses PBS/BSA
with 14.5% Optiprep for live cell samples and 27% Optiprep for a
variety of formalin fixed cell samples.
[0102] The performance of the optical switch method of cell sorting
in a microfluidic channel network is evaluated by the throughput,
purity and recovery of the sort as previously described. The
cartridge described in FIG. 20 is optimized to allow measurement of
the performance, since it is made of acrylic, the bottoms of the
target and waste collection reservoirs are transparent and the
cells that are sorted into these reservoirs can be quantified as to
both number and fluorescence labeling using an inverted
fluorescence microscope. Several of the switching configurations
described in FIGS. 3-11 were evaluated. These evaluations were
performed using a 50:50 mix of live HeLa:HeLa-GFP cells that was
sorted using either a 1- or 2-sided stationary laser spot, or a
0.degree. or 8.degree. 1-sided laser sweep. The laser was swept at
240 Hz. The laser ON time was 4 msec and the laser power was 20 W
for all switch modes. For the swept spot method, the focused IR
laser spot was translated about 70 .mu.m along the main
channel.
[0103] As shown in FIG. 22, the bi-directional optical switch with
laser spots, described in FIG. 6, gave good results for purity and
recovery for the 50:50 mixes of target:non-target cells up to a
throughput of 50 cells/s. However, at lower subpopulation
concentrations (data not shown), it was not an efficient use of
laser power to switch non-target cells, and coincidence errors
increased at higher cell throughput rates. Additionally, small
particulates that were not switched would contaminate the target
reservoir.
[0104] FIG. 22 also shows the performance of the 1-sided switching
methods, described in FIG. 9, with a stationary laser spot or a
spot that is translated in the direction of flow, either parallel
or at a slight angle to the flow. The sample core flow stream was
biased to the waste outlet such that all the cells went to waste by
default in the absence of the optical switch. Both of these methods
gave improved performance, as shown by the plots. The fact that the
performance of these two methods crosses, suggests that the
triggering of the optical switch was not optimal, and suggests that
the active triggering of the optical switch as described in FIGS.
10 and 11 will improve performance.
[0105] FIG. 23 shows an example of a pneumatic fluidic switch that
serves to sort cells or particles in a 1.times.2 microfluidic
channel network, i.e., a network with one main input channel and
two output channels extending from the bifurcating junction. A "Y"
geometry for the bifurcation junction is shown in FIG. 23, but
other bifurcations such as a "T" geometry may also be used. In
general these microfluidic channels are produced in optically
transparent substrates to enable projection of cell detection
optics into the channel. This substrate is typically, but not
limited to, glass, quartz, plastics, e.g., polymethylmethacrylate
(PMMA), etc., and other castable or workable polymers (e.g.
polydimethylsiloxane, PDMS or SU8). The depth of the microfluidic
channels is typically in, but not limited to, the range 10 .mu.m to
100 .mu.m. The width of the microfluidic channels is typically, but
not limited to, 1 to 5 times the depth. The cross section is
typically rectangular, or rectangular with quarter-round corners in
the case of microfluidic channels produced by photolithographic
masking of glass substrate followed by isotropic etching of the
channels.
[0106] The flow conditions are set such that pneumatic pressures
P0>P1>P2 and cells in fluid flow preferentially from highest
pressure to lowest pressure. When pressure P is increases such that
P0>P2>P1, then fluid flow is perturbed and reestablishes
equilibrium when fluid preferentially flows down the opposite
branch of the "Y" junction. The system can be returned to its
original state by restoring the P0>P1>P2 relationship.
[0107] The performance of the soiling mechanism in terms of
throughput (the temporal rate of cells entering the sorting region
at the top of the bifurcation junction) is limited by the
back-propagation of the fluid as shown in FIG. 23. When the fluidic
switch is activated, the particle motion is seen to reverse
direction and flow upstream before establishing a new flow path.
The time delay induced by this motion limits the speed of the
switch and the frequency of events to achieve acceptable yield
efficiency (the fraction of target cells in the target output
channel) and purity (the ratio of the number of target cells to the
total number of cells in the target output channel).
[0108] FIG. 24 shows one embodiment of a two-channel fluidic switch
that serves to sort cells in a 1.times.2 microfluidic channel
network, i.e. a network with one main input channel and two output
channels extending from a bifurcation junction. A "Y" geometry for
the bifurcation junction is shown in FIG. 24, but other
bifurcations such as a "T" geometry may also be used. A pair of
lateral flow channels are positioned between an analysis region and
the bifurcation junction. The lateral flow channels may be
symmetric in dimension or one side may be larger than the other to
support faster switching in one direction. In general these
microfluidic channels are produced in optically transparent
substrates to enable projection of cell detection optics into the
channel. This substrate is typically, but not limited to, glass,
quartz, plastics, e.g., polymethylmethacrylate (PMMA), etc., and
other castable or workable polymers (e.g. polydimethylsiloxane,
PDMS or SU8). The depth of the microfluidic channels is typically
in, but not limited to, the range 10 .mu.m to 100 .mu.m. The width
of the microfluidic channels is typically, but not limited to, 1 to
5 times the depth. The cross section is typically rectangular, or
rectangular with quarter-round corners in the case of microfluidic
channels produced by photolithographic masking of glass substrate
followed by isotropic etching of the channels.
[0109] The flow conditions are set such that when the fluidic
switch, in this case from pneumatic pressure, is turned off so that
the pressures P3=P4 in the junction region, all cells will
preferentially flow into one of the output channels, for example
the right output channel. When the fluidic switch is turned on
changing pressure such that P3>P4, a plug of fluid displaces the
flow stream such that the cells in proximity of the fluid plug are
directed into the left output channel. The setting and control of
the flow conditions in the microfluidic channel network can be
achieved by direct drive pumping, pneumatic pumping,
electro-kinetics, capillary action, gravity, or other means to
generate fluidic flow.
[0110] The performance of the sorting mechanism in terms of
throughput the temporal rate of cells entering the sorting region
at the top of the bifurcation junction), yield efficiency (the
fraction of target cells in the target output channel, 12), and
purity (the ratio of the number of target cells to the total number
of cells in the target output channel, 12), are impacted by various
factors, each of which affects the implementation of the optical
switch. The fluidic switch can be characterized by several
parameters such as the pressure differential (P4 vs. P3) projected
into the sorting junction region of the microfluidic channel
network, the position of the switching channels with respect to the
bifurcation junction, the duration of activation of the fluidic
switch, the maximum pressure used to produce the fluid
displacement, etc. The selection of particular values of these
parameters for the fluidic switch is a critical function of, among
other things, the topology and geometry of the microfluidic channel
system, the flow rates (cell velocities) within the microchannel
system, the ability to control the position of cells flowing in the
main channel (whether they are flowing in the center of the main
channel or off-set to one side), the amount of displacement of the
cells necessary to achieve reliable switching, the depth of the
channels, the shape of the channels, and the forces produced by the
cells' interactions with the optical switch.
[0111] FIG. 25 shows one embodiment of a one-channel fluidic switch
that serves to sort cells in a 1.times.2 microfluidic channel
network, i.e. a network with one main input channel and two output
channels extending from a bifurcation junction. A "Y" geometry for
the bifurcation junction is shown in FIG. 25, but other
bifurcations such as a "T" geometry may also he used. A single
lateral flow channel may be positioned on either side of the main
channel between the analysis region and the bifurcation. In general
these microfluidic channels are produced in optically transparent
substrates to enable projection of cell detection optics into the
channel. This substrate is typically, but not limited to, glass,
quartz, plastics, e.g., polymethylmethacrylate (PMMA), etc., and
other castable or workable polymers (e.g. polydimethylsiloxane,
PDMS or SU8). The depth of the microfluidic channels is typically
in, but not limited to, the range 10 .mu.m to 100 .mu.m. The width
of the microfluidic channels is typically, but not limited to, 1 to
5 times the depth. The cross section is typically rectangular, or
rectangular with quarter-round corners in the case of microfluidic
channels produced by photolithographic masking of glass substrate
followed by isotropic etching of the channels.
[0112] The flow conditions are set such that when the fluidic
switch, in this case from pneumatic pressure, is turned off so that
the pressure in the junction region is neutral, all cells will
preferentially flow into the output channel on the same side as the
lateral channel, in this case for example, the right output
channel. When the fluidic switch is turned on changing pressure
such that P3>P2, a plug of fluid displaces the flow stream such
that the cells in proximity of the fluid plug are directed into the
left output channel. The setting and control of the flow conditions
in the microfluidic channel network can be achieved by direct drive
pumping, pneumatic pumping, electro-kinetics, capillary action,
gravity, or other means to generate fluidic flow.
[0113] A preferred embodiment of a one-channel fluidic switch is
shown in FIG. 26. An off-set flow is achieved by having the right
channel wider than the left channel. The switch channel is also
wider than the primary channel along the majority of its path
length and tapers at the point of fluid insertion. This lowers the
peak amplitude of the applied pneumatic pressure necessary to
achieve sorting by concentrating the force on a smaller cross
sectional area. This allows for faster operation and improved
throughput.
[0114] The performance of the sorting mechanism in terms of
throughput (the temporal rate of cells entering the sorting region
at the top of the bifurcation junction), yield efficiency (the
fraction of target cells in the target output channel), and purity
(the ratio of the number of target cells to the total number of
cells in the target output channel), are impacted by various
factors, each of which affects the implementation of the optical
switch. The fluidic switch can be characterized by several
parameters such as the maximum pressure projected into the sorting
junction region of the microfluidic channel network, the position
of the switching channels with respect to the bifurcation junction,
the duration of activation of the fluidic switch, etc. The
selection of particular values of these parameters for the fluidic
switch is a critical function of, among other things, the topology
and geometry of the microfluidic channel system, the flow rates
(cell velocities) within the microchannel system, the ability to
control the position of cells flowing in the main channel (whether
they are flowing in the center of the main channel or off-set to
one side), the amount of displacement of the cells necessary to
achieve reliable switching, the depth of the channels, and the
shape of the channels. For mammalian cells, channels with cross
sections of approximately 50 .mu.m.times.150 .mu.m with pressure
drops of 0.5 to 1.0 psi over path lengths of 20-50 mm will achieve
flow velocities of 1-5 .mu.L per minute and use of switching
pressures of 1-3 psi is sufficient to achieve switching rates of
hundreds of events per second. For general application to particles
of 100 nm to 100 .mu.m, typical pressure drops for sample and
sheath flow are in the range of 0.1 to 10 psi over path lengths of
10 to 100 mm. A ratio of 2:1 for sheath to target pressures is
selected with the current chip design to ensure appropriate pinch
of the sample stream. Channel cross sections can be made in the
range of 5 to 150 .mu.m deep by 10 to 1,000 .mu.m wide, depending
on the type of cell or particle being run through the chip.
[0115] FIG. 27 shows a two-valve switch configuration that allows
control over the maximum pressure, rise time, decay time and total
time of a pneumatic pressure pulse to actuate the fluidic switch.
Three ports may be connected to pneumatic pressure sources, ambient
air, or vacuum. For rapid switching, P1 is held at a high pressure
greater than ambient air and P2 and P3 are at ambient air. In the
neutral position, both valves are closed or off. When a switching
event is desired, the first valve opens, which applied pneumatic
pressure to the switch channel. A second valve opens after a brief
delay (e.g., less than 5-10 milliseconds), which rapidly bleeds the
excess pressure from P1 out of port P3. The first valve is closed
to bleed the remaining pressure in the switch channel to ambient
levels and then the second valve closes to return the system to its
neutral position. This allows the pneumatic pulse to be shorter
than the off-on-off cycle time of a single valve (e.g.,
approximately 5 to 10 milliseconds). Selecting a pressure P1 that
is several times greater than the maximum pressure desired (e.g., 8
psi for a pulse with a desired 2 psi peak) combined with ambient
air or vacuum at ports P2 and P3, the pneumatic pressure pulse may
be shaped for maximum performance of the fluidic switch.
[0116] FIG. 28 shows two valve configurations for the two-channel
fluidic switch in FIG. 24. In the first, a single valve modulates a
high pressure source, and the second channel is at ambient air. In
this configuration, the shortest possible pulse is determined by
the off-on-off cycle time of the valve (e.g., 5-10 milliseconds).
In the second configuration, a valve is placed on each lateral
channel of the fluidic switch. In this case, both valves may be
used to modulate external pressure sources. The second valve may be
opened after the first valve with a variable time delay that is
shorter than the off-on-off cycle time of the valves. In this way,
the pneumatic pressure pulse may be shortened to increase the speed
and performance of the fluidic switch.
[0117] A complete fluidic switch-based cell sorting instrument has
been constructed. Examples of measurements obtained using this
instrument are shown in FIGS. 30-31. In FIG. 31, fluorescent.
calibration beads (e.g., Spherotech SPHERO beads or BD Quantibrite
beads) were measured and show clear separation of six intensities.
Statistics of mean intensity, standard deviations and CV's are
consistent with the manufacturers' recommended values. FIG. 31
shows an example of sorting a cell population. In this example, a
target population of 1% Jurkat cells stained with CellTracker.TM.
Green (Invitrogen Corp.) were spiked into an unstained population
of Jurkat cells. The cells were sorted using a pressure of 0.3 psi
for the sample, 0.6 psi for the sheath buffer, and 1.5 psi for the
switching valve. Approximately 35 thousand cells were analyzed and
336 target cells were identified and sorted into the target well.
Inspection of the target reservoir found 331 target cells out of a
total of 369 cells. This results in a calculated recovery of 99%
and purity of 90%.
[0118] To operate microfluidic chips, an initial fluid priming of
all microfluidic channels is required in a manner that does not
trap bubbles or introduce dust particles, which impede flow. This
requires application of a reproducible volume of air at a steady
pneumatic pressure from a clean high pressurized air source.
Generally, dust-free systems like a clean bench or a laminar hood
are necessary for priming microfluidic devices. The device, a
priming station, shown in FIG. 32 satisfies those requirements in a
simple and economical way. A clamp on the priming station
physically holds a cartridge and provides sealing for high pressure
access. A small sub-micron pore filter is attached to the clamp to
supply high pressure air to a fluid filled reservoir without dust.
A removable syringe may be used to provide a controllable volume of
air or an automated valve connected to a high pressure source may
be used. This uniformly distributes a predetermined volume of
bubble-free fluid throughout the microfluidic channels.
[0119] FIG. 33 shows a method for dilution cloning of cells for
monitoring growth and separating clonal populations. Microwells
with a volume of a few nanoliters may be microfabricated using a
variety of materials, including but not limited to, glass, quartz,
plastics, e.g., polymethylmethacrylate (PMMA), etc., and other
castable or workable polymers (e.g. polydimethylsiloxane, PDMS or
SU8). The depth of the microfluidic channels is typically in, but
not limited to, the range 10 .mu.m to 100 .mu.m. The width of the
microfluidic channels is typically, but not limited to, 1 to 5
times the depth. The cross section is typically rectangular, or
rectangular with quarter-round corners in the case of microfluidic
channels produced by photolithographic masking of glass substrate
followed by isotropic etching of the channels. An example of an
array of nanowells is shown in FIG. 33. In this case, the wells are
100 .mu.m.times.100 .mu.m squares with a depth of 70 .mu.m and
fabricated using PDMS soft lithography. The wells are sterilized in
a plasma and inserted into a 24-well tissue culture plate. Cells in
suspended in media are loaded into each well and settle by gravity
into the nanowells where they may be monitored periodically to
observe growth kinetics or to harvest preferred clonal colonies at
a single time point. These wells also may be incorporated into the
output reservoirs of a sorting device as a fixed element or as a
removable insert.
[0120] FIG. 35 shows optical detection methods for cell/particle
counting inside a multi-phase microfluidic drop (for example,
cells/particles encapsulated in drops inside a microfluidic
channel). By applying suitable signal processing, the numbers of
cells/particles inside the drops can be detected based on signal
peaks from the cells/particles. In one method, the entire channel
is illuminated and a single detector measures a signal, such as
forward scatter, that indicates the presence or absence of a cell
in the drop. A more sophisticated detection uses an array of
forward scatter detectors arranged across the channel and
orthogonal to the direction of flow in order to provide a better
spatial resolution for counting and localizing the cells/particles
inside the drops. In yet another approach, dark field illumination
and imaging can be added to a single detector scatter measurement.
When forward scatter signal detects the front edge of the drops, a
CCD camera can be synchronized to take a dark field image of the
drops. The cells/particles will be bright spots in the images,
which can be processed and identified for counting.
[0121] In many sorting situations, the target population of cells
or particles may be small, but the surface area of the collection
reservoir is large. Particles may stick to the reservoir wall,
which reduces collection efficiency. FIG. 36 shows approaches to
minimizing the cell or particle interaction with surfaces. In one
method, sorted target cells are collected in a confined area that
displaces less volume than the fluid to minimize contact between
cells and collection reservoir walls. Due to surface tension,
collected liquid forms a drop wetted on the confined area. In
another method, the surface of the collection reservoir can made
hydrophobic by coating with a hydrocarbon or fluorocarbon-based
silanization. Because of the hydrophobic coating, the collected
liquid with cells or particles will be confined in a drop near
outlet holes. In another method, a separate, fitted but removable
container can be used for collection of sorted cells. This separate
container can he used for further treatment of cells, which will
minimize loss of cells while transferring sorted cells from
collection reservoir to another reservoir (a multi-well culture
plate, for example). The collection container has a hole on the
bottom to access to the outlet hole in microfluidic devices. The
diameter of the hole may be made less than one millimeter so that
surface tension prevents leaking through it. A gasket made of soft
material (for example, Silicone-based rubber, PDMS) is inserted
between the collection container and the microfluidic device for
sealing and bonding.
[0122] Often it is desired to recover samples after cytometric
analysis. FIG. 38 shows a microfluidic device that pinches cell
flow for analysis but recovers cells with less dilution. The sample
is flow focused using a sheath buffer, as shown in FIG. 2 and. FIG.
38. After the sample passes the analysis region, the microfluidic
channel splits into three channels. The center channel is the
sample recovery channel, and the channels to the left and right
collect the excess sheath buffer to reduce sample dilution. By
appropriate selection of channel widths and applied pressures, the
degree of sample dilutions may be adjusted from 1:1 dilution to the
dilution of the sheath flow (typically 1:20). Under some
conditions, i.e., very dilute samples, the collected specimen may
be concentrated instead.
[0123] FIG. 37 shows a microfluidic device design for multiple
sample analysis or sorting. This design does not require changing
cartridges or realignment after loading different samples that may
cause changes in the fluorescent background. This invention
includes three sample reservoirs two for samples and one for a
buffer to separate the two samples from cross contamination. By
adjusting pressure, each sample can be injected and pinched for
flow cytometric analysis. For example, with two samples A and B,
for an analysis of A the reservoir of sample A is applied with
highest pressure and the buffer reservoir is at an intermediate
pressure while the reservoir of sample B is kept at the lowest
pressure. By alternating which channel has the highest pressure,
the desired channel will flow to the analysis region (highest
pressure) or it will be inhibited from flowing (lowest pressure).
Pure buffer may be introduced between each sample to allow clear
separation of signals in the analysis region. The number of samples
that can be loaded and run sequentially can be increased by two for
each independent separation buffer channel added to the
microfluidic chip.
[0124] FIG. 38 also shows an example of a microfluidic device that
can multiplex two samples with adjustable dilution. This device
utilizes two sample channels, A and B, and a separation buffer. To
analyze sample A, the following pressure setting is used,
P_sw_A<P_sw_B<P_B<P_sb<P_A<P_sth. To analyze sample
B, the following pressure setting is used,
P_sw_B<P_sw_A<P_A<P_sb<P_B<P_sth. To prevent cross
contamination between samples, a separation buffer may be flown
down the channel in between measurements of Samples A and B. With
additional pressure ports, this design is scalable to three or more
samples. FIG. 38 shows an example of this device switching between
two samples.
[0125] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
arid understanding, it will be readily apparent to those of
ordinary skill in the art, in light of the teachings of this
invention, that certain changes and modifications may be made
thereto without departing from the spirit or scope of the
invention.
ENDNOTES
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