U.S. patent application number 14/027941 was filed with the patent office on 2014-01-16 for droplet actuator.
This patent application is currently assigned to Advanced Liquid Logic, Inc.. The applicant listed for this patent is Advanced Liquid Logic, Inc.. Invention is credited to Allen E. Eckhardt, Zhishan Hua, Michael G. Pollack, Vijay Srinivasan, Arjun Sudarsan.
Application Number | 20140014517 14/027941 |
Document ID | / |
Family ID | 40756098 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140014517 |
Kind Code |
A1 |
Srinivasan; Vijay ; et
al. |
January 16, 2014 |
Droplet Actuator
Abstract
Droplet actuator for conducting droplet operations, such as
droplet transport and droplet dispensing, is provided. In one
embodiment, the droplet actuator may include an electrode that is
rotationally but not reflectively symmetrical.
Inventors: |
Srinivasan; Vijay; (Durham,
NC) ; Pollack; Michael G.; (Durham, NC) ; Hua;
Zhishan; (Greensboro, NC) ; Sudarsan; Arjun;
(Cary, NC) ; Eckhardt; Allen E.; (Durham,
NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Liquid Logic, Inc. |
Research Triangle Park |
NC |
US |
|
|
Assignee: |
Advanced Liquid Logic, Inc.
Research Triangle Park
NC
|
Family ID: |
40756098 |
Appl. No.: |
14/027941 |
Filed: |
September 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12747231 |
Aug 25, 2010 |
8562807 |
|
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PCT/US08/86186 |
Dec 10, 2008 |
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14027941 |
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61012567 |
Dec 10, 2007 |
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61014128 |
Dec 17, 2007 |
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61092709 |
Aug 28, 2008 |
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Current U.S.
Class: |
204/601 |
Current CPC
Class: |
B01L 2200/061 20130101;
B01L 3/502761 20130101; B01L 3/502792 20130101; B01L 2400/0427
20130101; B01L 2300/16 20130101; B01L 2200/0605 20130101; B01L
2400/0415 20130101; B01L 2200/0647 20130101; B01L 2300/0645
20130101; G01N 27/44743 20130101; B01L 3/0268 20130101 |
Class at
Publication: |
204/601 |
International
Class: |
G01N 27/447 20060101
G01N027/447 |
Goverment Interests
GRANT INFORMATION
[0002] This invention was made with government support under
GM072155-02 and DK066956-02, both awarded by the National
Institutes of Health of the United States. The United States
Government has certain rights in the invention.
Claims
1. A droplet actuator comprising an electrode that is rotationally
but not reflectively symmetrical.
2. The droplet actuator of claim 1 comprising a path and/or array
of the electrodes.
3. The droplet actuator of claim 2 wherein the electrodes are
interdigitated.
4. The droplet actuator of claim 2 wherein the electrodes are not
interdigitated.
5. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 3.
6. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 4.
7. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 5.
8. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 6.
9. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 7.
10. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 8.
11. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 9.
12. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is 10.
13. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and X is greater than 10.
14. The droplet actuator of claim 1 wherein the rotational symmetry
is X-fold, and for each electrode X is 3, 4, 5, 6, 7, 8, 9, and/or
10.
15. The droplet actuator of claim 1 wherein the droplet actuator
comprises a path and/or array of the electrodes, wherein adjacent
electrodes are arranged such that no line can be drawn between two
adjacent electrodes without overlapping one or both of the two
adjacent electrodes.
16. The droplet actuator of claim 15 wherein the electrodes are not
interdigitated.
17. The droplet actuator of claim 15 wherein the electrodes are
interdigitated.
Description
RELATED APPLICATIONS
[0001] In addition to the patent applications cited herein, each of
which is incorporated herein by reference, this application is a
divisional of U.S. patent application Ser. No. 12/747,231, filed
Aug. 25, 2010, entitled "Droplet Actuator Configurations and
Methods", the application of which is a national phase application
of PCT/US2008/086186, filed on Dec. 12, 2008, entitled "Droplet
Actuator Configurations and Methods", the application of which
claims priority to: U.S. Provisional Application Nos.: 61/012,567,
filed on Dec. 10, 2007, entitled "Droplet Actuator Loading by
Displacement of Filler Fluid"; 61/014,128, filed on Dec. 17, 2007,
entitled "Electrode Configurations for a Droplet Actuator"; and
61/092,709, filed on Aug. 28, 2008, entitled "Electrode
Configurations for a Droplet Actuator;" the entire disclosures of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The invention relates to droplet actuators for conducting
droplet operations, such as droplet transport and droplet
dispensing, and to methods of loading and using such droplet
actuators.
BACKGROUND OF THE INVENTION
[0004] Droplet actuators are used to conduct a wide variety of
droplet operations, such as droplet transport and droplet
dispensing. A droplet actuator typically includes a substrate with
electrodes arranged for conducting droplet operations on a droplet
operations surface of the substrate. Electrodes may include droplet
operations electrodes and reference electrodes. Droplets subjected
to droplet operations on a droplet actuator may, for example, be
reagents and/or droplet fluids for conducting assays. There is a
need for improved functionality when conducting droplet operations
and for alternative approaches to configuring droplet actuators for
conducting droplet operations.
[0005] There are various ways of loading reagents and droplet
fluids into droplet actuators. Problems with such methods include
the risk of introducing air into the fluid and the inability to
reliably handle small droplet fluid volumes. Because of these and
other problems, there is a need for alternative approaches to
loading droplet fluids into a droplet actuator.
BRIEF DESCRIPTION OF THE INVENTION
[0006] The invention provides a droplet actuator. In one
embodiment, the droplet actuator may include a substrate including,
droplet operations electrodes arranged for conducting droplet
operations on a surface of the substrate; and reference electrodes
associated with the droplet operations electrodes and extending
above the surface of the substrate.
[0007] In another embodiment the droplet actuator may include two
substrates separated to form a gap. Droplet operations electrodes
may be associated with at least one of the substrates and arranged
for conducting droplet operations in the gap. Reference electrodes
may be associated with at least one of the substrates and extending
into the gap.
[0008] In yet another embodiment, the invention provides a droplet
actuator including a substrate including droplet operations
electrodes and reference electrodes configured for conducting
droplet operations, wherein at least a subset of the reference
electrodes is separated from a droplet operations surface by an
insulator and/or dielectric material.
[0009] In still another embodiment, the invention provides a
droplet actuator including two substrates separated to form a gap;
droplet operations electrodes associated with at least one of the
substrates and arranged for conducting droplet operations in the
gap; and reference electrodes. The reference electrodes may be
associated with at least one of the substrates; and separated from
a droplet operations surface of the substrate by an insulator
and/or a dielectric material.
[0010] Further, the invention provides a droplet actuator including
a substrate, which may have droplet operations electrodes
configured for conducting one or more droplet operations; and
reference electrodes inset into and/or between and/or
interdigitated with one or more droplet operations electrodes. A
reference electrode may be inset into a droplet operations
electrode. A reference electrode may be inset between two or more
droplet operations electrodes. A reference electrode may be
interdigitated with a droplet operations electrode.
[0011] The invention provides droplet operations electrodes that
are rotationally but not reflectively symmetrical. These electrodes
may be formed into paths and/or arrays. These electrodes are
interdigitated. In some cases, these electrodes are not
interdigitated. The rotational symmetry may in certain embodiments
be X-fold, where X is 3, 4, 5, 6, 7, 8, 9, or 10. The rotational
symmetry may in certain embodiments be X-fold, where X is greater
than 10. In some cases, adjacent electrodes are arranged such that
no straight line can be drawn between two adjacent electrodes
without overlapping one or both of the two adjacent electrodes. In
some cases, adjacent electrodes are not interdigitated but are
arranged such that no straight line can be drawn between two
adjacent electrodes without overlapping one or both of the two
adjacent electrodes.
[0012] The invention also provides a droplet actuator including an
electrode having a shape that comprises a section of a rotationally
but not reflectively symmetrical shape, the electrode having X-fold
rotational symmetry, where X is 5, 6, 7, 8, 9, 10 or more. A
droplet actuator may include a path or array including one or more
of such electrodes.
[0013] The invention provides a droplet actuator including top and
bottom substrates separated to form a gap, each substrate including
electrodes configured for conducting droplet operations, the gap
arranged to provide a distance between the substrates sufficient to
permit independent droplet operations on a droplet operations
surface of each substrate. The top substrate may, in some
embodiments, include an arrangement of electrodes that is
substantially congruent with an arrangement of electrodes on the
bottom substrate. The top substrate may, in some embodiments,
include an arrangement of electrodes that is substantially
congruent with and in registration with an arrangement of
electrodes on the bottom substrate. In some embodiments, the gap is
sufficiently wide that: one or more droplets having a footprint
which is from about 1 to about 5 times the size of the footprint of
a droplet operations electrode can be subjected to droplet
operations on the droplet operations surface of the top substrate
without contacting the droplet operations surface of the bottom
substrate; and one or more droplets having a footprint which is
from about 1 to about 5 times the size of the footprint of a
droplet operations electrode can be subjected to droplet operations
on the droplet operations surface of the bottom substrate without
contacting the droplet operations surface of the top substrate.
[0014] The invention also provides a droplet actuator including: a
first substrate including droplet operations electrodes configured
for conducting one or more droplet operations; a second substrate
including: a conductive layer at least partially contiguous with
two or more of the droplet operations electrodes; and a
perfluorophosphonate coating overlying at least a portion of the
conductive layer. The first substrate and the second substrate are
separated to form a gap for conducting droplet operations mediated
by the droplet operations electrodes. The conductive layer may in
some embodiments include indium tin oxide or a substitute
therefor.
[0015] The invention further provides a droplet actuator including:
two surfaces separated to form a gap; electrodes associated with
one or more surfaces and arranged for conducting one or more
droplet operations; a filler fluid in the gap; a reservoir
including a droplet fluid in the reservoir; a fluid path from the
reservoir into the gap; and optionally, an filler fluid opening
arranged for permitting fluid to exit the gap and/or exit one
portion of the gap into another portion of the gap; a pressure
source configured to force dislocation of filler fluid in the gap
and/or through the filler fluid opening and thereby force droplet
fluid from the reservoir through the fluid path into the gap.
[0016] The pressure source may be configured such that the
dislocation of filler fluid forces droplet fluid from the reservoir
through the fluid path into the gap into sufficient proximity with
one or more of the electrodes to enable one or more droplet
operations to be mediated by the one or more of the electrodes. The
pressure source may include a negative pressure source and/or a
positive pressure source. In some cases, multiple reservoirs are
provided, each arranged to permit a droplet fluid to be loaded into
the gap. The droplet operation may, for example, include a droplet
dispensing operation in which a droplet is dispensed from the
droplet fluid.
[0017] The invention also provides a method of loading a droplet
actuator, the method including providing: a droplet actuator loaded
with a filler fluid; a reservoir including a droplet fluid; a fluid
path extending from the reservoir into the droplet actuator;
forcing filler fluid: from one locus in the droplet actuator to
another locus in the droplet actuator; or out of the droplet
actuator; thereby causing droplet fluid to flow through the fluid
path and into the droplet actuator. Droplet fluid may be forced
into sufficient proximity with one or more electrodes to enable one
or more droplet operations to be mediated in the droplet actuator
by the one or more electrodes. Filler fluid may be forced using a
negative and/or positive pressure source. In some cases, multiple
droplet fluids are loaded from multiple reservoirs. The droplet
operation may, for example, include a droplet dispensing operation
in which a droplet is dispensed from the droplet fluid.
[0018] The invention also provides a method of conducting a droplet
operation on a droplet actuator, the method including: using a
negative pressure to flow a source fluid into a droplet actuator
gap into proximity with a droplet operations electrode; and using
the droplet operations electrode along with other droplet
operations electrodes to conduct the droplet operation. The droplet
operation can include dispensing a droplet from the source
fluid.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 illustrates a side view of a section of a droplet
actuator including a top substrate and a bottom substrate that are
separated to form a gap therebetween, and including reference
electrodes provided as exposed posts or pillars that protrude
through insulator layer and into the gap.
[0020] FIG. 2 illustrates a side view of a section of droplet
actuator that is substantially the same as the droplet actuator
shown in FIG. 1, except that reference electrodes that protrude
through the insulator layer are replaced with reference electrodes
that extend into but do not protrude through insulator layer.
[0021] FIG. 3 illustrates a side view of a section of a droplet
actuator that includes a top substrate and a bottom substrate that
are arranged having a gap therebetween, and including a reference
electrode associated with the top substrate atop which is provided
an insulator layer.
[0022] FIG. 4A illustrates an electrode pattern for a droplet
actuator, including electrodes which are substantially H-shaped,
leaving gaps in top and bottom regions for reference
electrodes.
[0023] FIG. 4B illustrates an electrode pattern in which electrodes
are shaped to provide a gap between each adjacent pair of
electrodes, and reference electrodes are inset between electrodes
rather than inset into electrodes as shown in (FIG. 4A).
[0024] FIGS. 5A, 5B, 5C, 5D and 5E illustrate electrode patterns in
which the electrodes are overlapping, but not interdigitated, in
order to facilitate droplet overlap with adjacent electrodes.
[0025] FIG. 6 illustrates a side view of a droplet actuator in
which droplets may be subjected to droplet operations along both
substrates (top and bottom).
[0026] FIG. 7 illustrates an embodiment in which the loading
opening is connected to the reservoir by a narrow channel of width
w, patterned in the spacer material.
[0027] FIGS. 8A and 8B illustrate a side view and top view (not to
scale), respectively, of a droplet actuator configured to make use
of negative displacement of filler fluid for droplet fluid
loading.
[0028] FIGS. 9A, 9B, and 9C illustrate a method of loading a
droplet actuator using droplet fluid source and a negative pressure
device.
[0029] FIGS. 10A and 10B illustrate the use of a negative pressure
device of loading assembly constituted by a threaded negative
pressure opening with a screw.
[0030] FIGS. 11A and 11B illustrate FIGS. 11A a negative pressure
loading implementation similar to those described in FIGS. 8 and 9,
except that the negative pressure opening and the negative pressure
device of the loading assembly is replaced with a negative pressure
opening that includes a septum and an absorbent material.
[0031] FIGS. 12A and 12B illustrate side views of a droplet
actuator that uses a capillary as a negative pressure opening.
[0032] FIGS. 13A and 13B illustrate a side view and top view,
respectively, of a droplet actuator with sealed vent holes.
DEFINITIONS
[0033] As used herein, the following terms have the meanings
indicated.
[0034] "Activate" with reference to one or more electrodes means
effecting a change in the electrical state of the one or more
electrodes which in the presence of a droplet results in a droplet
operation.
[0035] "Droplet" means a volume of liquid on a droplet actuator
that is at least partially bounded by filler fluid. For example, a
droplet may be completely surrounded by filler fluid or may be
bounded by filler fluid and one or more surfaces of the droplet
actuator. Droplets may, for example, be aqueous or non-aqueous or
may be mixtures or emulsions including aqueous and non-aqueous
components. Droplets may take a wide variety of shapes; nonlimiting
examples include generally disc shaped, slug shaped, truncated
sphere, ellipsoid, spherical, partially compressed sphere,
hemispherical, ovoid, cylindrical, and various shapes formed during
droplet operations, such as merging or splitting or formed as a
result of contact of such shapes with one or more surfaces of a
droplet actuator.
[0036] "Droplet Actuator" means a device for manipulating droplets.
For examples of droplets, see U.S. Pat. No. 6,911,132, entitled
"Apparatus for Manipulating Droplets by Electrowetting-Based
Techniques," issued on Jun. 28, 2005 to Pamula et al.; U.S. patent
application Ser. No. 11/343,284, entitled "Apparatuses and Methods
for Manipulating Droplets on a Printed Circuit Board," filed on
filed on Jan. 30, 2006; U.S. Pat. No. 6,773,566, entitled
"Electrostatic Actuators for Microfluidics and Methods for Using
Same," issued on Aug. 10, 2004 and U.S. Pat. No. 6,565,727,
entitled "Actuators for Microfluidics Without Moving Parts," issued
on Jan. 24, 2000, both to Shenderov et al.; Pollack et al.,
International Patent Application No. PCT/US2006/047486, entitled
"Droplet-Based Biochemistry," filed on Dec. 11, 2006, the
disclosures of which are incorporated herein by reference. Methods
of the invention may be executed using droplet actuator systems,
e.g., as described in International Patent Application No.
PCT/US2007/009379, entitled "Droplet manipulation systems," filed
on May 9, 2007. In various embodiments, the manipulation of
droplets by a droplet actuator may be electrode mediated, e.g.,
electrowetting mediated or dielectrophoresis mediated.
[0037] "Droplet operation" means any manipulation of a droplet on a
droplet actuator. A droplet operation may, for example, include:
loading a droplet into the droplet actuator; dispensing one or more
droplets from a source droplet; splitting, separating or dividing a
droplet into two or more droplets; transporting a droplet from one
location to another in any direction; merging or combining two or
more droplets into a single droplet; diluting a droplet; mixing a
droplet; agitating a droplet; deforming a droplet; retaining a
droplet in position; incubating a droplet; heating a droplet;
vaporizing a droplet; condensing a droplet from a vapor; cooling a
droplet; disposing of a droplet; transporting a droplet out of a
droplet actuator; other droplet operations described herein; and/or
any combination of the foregoing. The terms "merge," "merging,"
"combine," "combining" and the like are used to describe the
creation of one droplet from two or more droplets. It should be
understood that when such a term is used in reference to two or
more droplets, any combination of droplet operations sufficient to
result in the combination of the two or more droplets into one
droplet may be used. For example, "merging droplet A with droplet
B," can be achieved by transporting droplet A into contact with a
stationary droplet B, transporting droplet B into contact with a
stationary droplet A, or transporting droplets A and B into contact
with each other. The terms "splitting," "separating" and "dividing"
are not intended to imply any particular outcome with respect to
size of the resulting droplets (i.e., the size of the resulting
droplets can be the same or different) or number of resulting
droplets (the number of resulting droplets may be 2, 3, 4, 5 or
more). The term "mixing" refers to droplet operations which result
in more homogenous distribution of one or more components within a
droplet. Examples of "loading" droplet operations include
microdialysis loading, pressure assisted loading, robotic loading,
passive loading, and pipette loading. In various embodiments, the
droplet operations may be electrode mediated, e.g., electrowetting
mediated or dielectrophoresis mediated.
[0038] "Filler fluid" means a fluid associated with a droplet
operations substrate of a droplet actuator, which fluid is
sufficiently immiscible with a droplet phase to render the droplet
phase subject to electrode-mediated droplet operations. The filler
fluid may, for example, be a low-viscosity oil, such as silicone
oil. Other examples of filler fluids are provided in International
Patent Application No. PCT/US2006/047486, entitled, "Droplet-Based
Biochemistry," filed on Dec. 11, 2006; and in International Patent
Application No. PCT/US2008/072604, entitled "Use of additives for
enhancing droplet actuation," filed on Aug. 8, 2008.
[0039] The terms "top" and "bottom" are used throughout the
description with reference to the top and bottom substrates of the
droplet actuator for convenience only, since the droplet actuator
is functional regardless of its position in space.
[0040] When a liquid in any form (e.g., a droplet or a continuous
body, whether moving or stationary) is described as being "on",
"at", or "over" an electrode, array, matrix or surface, such liquid
could be either in direct contact with the
electrode/array/matrix/surface, or could be in contact with one or
more layers or films that are interposed between the liquid and the
electrode/array/matrix/surface.
[0041] When a droplet is described as being "on" or "loaded on" a
droplet actuator, it should be understood that the droplet is
arranged on the droplet actuator in a manner which facilitates
using the droplet actuator to conduct one or more droplet
operations on the droplet, the droplet is arranged on the droplet
actuator in a manner which facilitates sensing of a property of or
a signal from the droplet, and/or the droplet has been subjected to
a droplet operation on the droplet actuator.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The invention provides modified droplet actuators, as well
as methods of making and using such droplet actuators. Among other
things, the droplet actuators and methods of the invention provide
improved functionality when conducting droplet operations and
alternative approaches to configuring droplet actuators for
conducting droplet operations. The invention also provides improved
loading configurations for droplet actuators, as well as improved
methods of loading droplet actuators, and reliable handling small
droplet fluid volumes.
[0043] FIG. 1 illustrates a side view of a section of droplet
actuator 100. Droplet actuator 100 includes a top substrate 110 and
a bottom substrate 120 that are separated to form a gap 124
therebetween. The top substrate may or may not be present. A set of
droplet operations electrodes 128, e.g., electrodes 128a, 128b, and
128c, are associated with bottom substrate 120. In one embodiment,
the droplet operations electrodes comprise electrowetting
electrodes. An insulator layer 132 is provided atop bottom
substrate 120 and electrodes 128. Insulator layer 132 may be formed
of any dielectric material, such as polyimide. Additionally, a set
of reference electrodes 136 (e.g., reference electrodes 136a, 136b,
and 136c) are arranged between electrodes 128, as shown in FIG. 1.
A hydrophobic layer (not shown) may be disposed atop insulator
layer 132.
[0044] Reference electrodes 136 are provided as exposed posts or
pillars that protrude through insulator layer 132 and into gap 124
where the reference electrodes may contact the droplet 140. The
function of the reference electrodes 136 is to bias droplet 140 at
the ground potential or another reference potential. The reference
potential may, for example, be a ground potential, a nominal
potential, or another potential that is different than the
actuation potential applied to the droplet operations electrodes.
In a related embodiment, the tops of reference electrodes 136 are
substantially flush the insulator layer 132. In another related
embodiment, the tops of reference electrodes 136 are substantially
flush with the hydrophobic layer (not shown). In yet another
related embodiment, the tops of reference electrodes 136 are
substantially flush with insulator layer 132, and the hydrophobic
layer (not shown) overlies the tops of reference electrodes 136.
Further, in another related embodiment, the tops of reference
electrodes 136 lie within insulator layer 132 but below a top
surface of insulator layer 132, e.g., as illustrated in FIG. 2.
[0045] FIG. 2 illustrates a side view of a section of droplet
actuator 200. Droplet actuator 200 is substantially the same as
droplet actuator 100 of FIG. 1, except that reference electrodes
136 of droplet actuator 100 that protrude through insulator layer
132 are replaced with reference electrodes 210 (e.g., reference
electrodes 210a, 210b, and 210c) that extend into but do not
protrude through insulator layer 132. The inventors have
unexpectedly found that droplet operations can be conducted using
insulated reference electrodes by inducing a voltage in the droplet
(e.g., by fringing fields). Using insulated reference electrodes
has the advantage that the device is easier to manufacture (e.g.,
no patterning of the insulator layer 132 is required).
[0046] In one embodiment of FIG. 2, the top substrate 110 may
include a conductive coating (not shown) over some portion or all
of the surface exposed to the droplet actuator. An example of such
a conductive coating is indium tin oxide (ITO). The conductive
coating may be electrically connected to reference electrode 210
through a resistor or a capacitor. The capacitor may be formed
between the conductive coating and reference electrode 210 (serving
as the plates of the capacitor) with the insulator layer 132 and as
the gap 124 serving as a composite dielectric. In one embodiment,
portions of the reference electrode 210 are not covered with the
insulator 132. In another embodiment, portions of the reference
electrode 210 are not covered with the insulator 132 and protrude
through the substrate as shown in FIG. 1. In yet another
embodiment, the insulated reference electrodes may be provided on
the top substrate 110, e.g., as illustrated in FIG. 3.
[0047] FIG. 3 illustrates a side view of a section of droplet
actuator 300. Droplet actuator 300 includes a top substrate 310 and
a bottom substrate 320 that are arranged having a gap 324
therebetween. A set of electrodes 328 (e.g., electrodes 328a, 328b,
and 328c) are associated with bottom substrate 320. An insulator
layer 332 is provided atop bottom substrate 320 and electrodes 328.
Additionally, a reference electrode 336 is associated with top
substrate 310 atop which is provided an insulator layer 340.
Insulator layers 332 and 340 may be formed of any dielectric
material, such as polyimide. A hydrophobic coating (not shown) may
be disposed on the surface of the insulator exposed to the gap. In
certain embodiments the thickness of insulator 332 is larger than
the thickness of insulator 340 by for example a factor of 2, 3, 4,
5, 10, 25, 50, 100. The factor need not be an integer and can be
fractions. The larger the factor the lower the voltage required for
droplet operations. Embodiments shown in FIG. 2 and FIG. 3 can also
be combined to result in a device with reference electrodes on both
substrates. The reference elements may be electrically connected to
each other through a resistor or a capacitor. The capacitor may be
formed between the two reference electrodes (serving as the plates
of the capacitor) with the insulator layer 332 and as the gap 324
serving as a composite dielectric.
[0048] As noted with respect to droplet actuator 200 of FIG. 2, the
inventors have unexpectedly found that droplet operations can be
conducted using insulated reference electrodes by inducing a
voltage in the droplet.
[0049] In one embodiment, the dielectric material is a hydrophobic
material. For example, fluorinated ethylene propylene (FEP;
available from DuPont as Teflon.RTM. FEP) is a suitable hydrophobic
material. The hydrophobic material may, in some embodiments, serve
as both the dielectric and the hydrophobic coating. This embodiment
improves ease of manufacture, since an additional hydrophobic
coating is not required. In a related embodiment, the dielectric
material includes a laminated film. FEP also serves as an example
of a laminated film. Using a film dielectric which is hydrophobic
facilitates use perfluorinated solvents as filler fluids.
Perfluorinated solvents are ideal filler fluids for many
applications, since they are immiscible with both aqueous and
organic liquids. Thus, aqueous and organic droplets can be
subjected to droplet operations in such an environment.
[0050] Thus, the invention also provides a method of conducting a
droplet operation on an organic droplet in a droplet actuator
loaded with perfluorinated solvent as a filler fluid. For example,
the method provides for dispensing one or more organic droplets
from a source organic droplet; splitting, separating or dividing an
organic droplet into two or more organic droplets; transporting an
organic droplet from one location to another in any direction;
merging or combining two or more organic droplets into a single
droplet; diluting an organic droplet; mixing an organic droplet;
agitating an organic droplet; deforming an organic droplet;
retaining an organic droplet in position; incubating an organic
droplet; heating an organic droplet; vaporizing an organic droplet;
condensing an organic droplet from a vapor; cooling an organic
droplet; disposing of an organic droplet; transporting an organic
droplet out of a droplet actuator; other droplet operations
described herein; and/or any combination of the foregoing; in each
case on a droplet actuator in which the droplet operations surface
is coated with, in contact with or flooded with a perfluorinated
solvent. The foregoing operations are suitably conducted on a
droplet operations surface that is composed of or is coated with a
hydrophobic perfluorinated solvent-tolerant coating, such as
FEP.
[0051] FIG. 4A illustrates an electrode pattern 400 for a droplet
actuator (not shown). Droplet actuator 400 includes a set of
electrodes 410. Electrodes 410 are substantially H-shaped, leaving
gaps in top and bottom regions for references electrodes 414.
Reference electrodes 414 are inset into the gaps in electrodes 410.
As shown, gaps are provided on two sides of electrodes 410; however
in some embodiments, gaps may be provided on only one side or on
more than two sides. Further, the illustrated electrodes show
single gaps with single reference electrodes inset therein;
however, it will be appreciated that multiple gaps may be provided,
and in some embodiments, the electrode 410 and the reference
electrode 414 may be substantially interdigitated. Electrodes 410
may be used to conduct one or more droplet operations.
[0052] Reference electrodes 414 may be exposed to the gap, and in
some cases, they may protrude into the gap, e.g., as described with
reference to reference electrodes 136 of FIG. 1 or they may be
insulated, e.g., as described with reference to FIGS. 2 and 3.
[0053] One or more insulated wires 418 provide an electrical
connection to reference electrodes 414. FIG. 4A shows a droplet 420
that is being manipulated along electrodes 410 using reference
electrodes 414.
[0054] In one embodiment, the top or bottom substrate may include a
conductive coating over some portion or all of the surface exposed
to the droplet actuator. An example of such a conductive coating is
indium tin oxide (ITO). The conductive coating may itself be coated
with a hydrophobic layer. A variety of materials are suitable for
coating the conductive layer to provide a hydrophobic surface. One
example is a class of compounds known as perfluorophosphonates.
Perfluorophosphonates may be useful for establishing a hydrophobic
layer over a conductive layer, such as a metal. In one embodiment,
a perfluorophosphonate is used to form a substantial monolayer over
the conductive layer.
[0055] For example, a droplet actuator may include a metal
conducting layer coated with a perfluorophosphonate exposed to a
region in which droplets are subjected to droplet operations.
Similarly, a droplet actuator may include a metal conducting layer
coated with a perfluorophosphonate monolayer exposed to a region in
which droplets are subjected to droplet operations. The
perfluorophosphonate may be deposited on the conducting layer in an
amount which facilitates the conducting of droplet operations. The
perfluorophosphonate layer may reduce fouling during droplet
operations relative to fouling that would occur in the absence of
the phosphonate or perfluorophosphonate coating. The conducting
layer may, in some embodiments, include ITO.
[0056] As another example, a droplet actuator comprising two
substrates separated to form a gap, each substrate comprising
electrodes configured for conducting droplet operations, may
include ITO on a top substrate coated with a
perfluorophosphonate.
[0057] A suitable perfluorophosphonate for use in accordance with
the invention is 1-phosphonoheptadecafluorooctane
(CF.sub.3(CF.sub.2).sub.7PO.sub.3H.sub.2). This material can be
synthesized using known methods starting with
1-bromoheptadecafluorooctane (CF.sub.3(CF.sub.2).sub.7Br). Similar
molecules of varying lengths can be synthesized using well-known
techniques starting with known precursors.
[0058] FIG. 4B illustrates an electrode pattern 450 for a droplet
actuator (not shown). Droplet actuator 450 is substantially the
same as droplet actuator 400 of FIG. 4A, except that the geometries
of electrodes 410 and the inset reference electrodes 414 differ
from the electrode geometries illustrated in FIG. 4A. Electrodes
410 in FIG. 4B are shaped to provide a gap between each adjacent
pair of electrodes 410. Electrodes 414 are inset between electrodes
410 rather than inset into electrodes 410.
[0059] As described above with reference to FIG. 1A, reference
electrodes 414 in FIG. 4B may also be exposed to the gap, and in
some cases, they may protrude into the gap, e.g., as described with
reference to reference electrodes 136 of FIG. 1 or they may be
insulated, e.g., as described with reference to FIGS. 2 and 3. One
or more insulated wires 418 provide an electrical connection to
reference electrodes 414. FIG. 4B shows a droplet 420 that is being
manipulated along electrodes 410 using reference electrodes 414.
Electrodes 410 may be used to conduct one or more droplet
operations.
[0060] FIGS. 5A, 5B, 5C, 5D and 5E illustrate electrode patterns
510, 520, 530, 540, and 550, respectively, which are yet other
nonlimiting examples of electrode configurations of the invention.
Electrode patterns 510, 520, 530, 540, and 550 illustrate
configurations in which the electrodes are overlapping, but not
interdigitated, in order to facilitate droplet overlap with
adjacent electrodes. These electrode patterns can be combined with
reference electrodes that are also inset into and/or between and/or
interdigitated with the electrodes, e.g., as described with
reference to FIG. 4. The illustrated overlapping electrodes exhibit
rotational symmetry. The examples illustrated in FIG. 5 show
four-fold rotational symmetry, but it will be appreciated that the
overlapping electrodes may exhibit a rotational symmetry which is
X-fold, where X is 3, 4, 5, 6, 7, 8, 9, 10 or greater. Further, a
droplet actuator may combine electrodes with different X-fold
rotational symmetries.
[0061] Electrodes with rotational symmetry are preferred for
overlapping electrodes, since the symmetry causes the droplets to
be centered over the electrode. Further, the droplet shape will
also have rotational symmetry, which permits overlap with adjacent
electrodes or reference elements in all directions. In some
embodiments, one or more of the electrodes have rotational symmetry
but not reflection symmetry. In another embodiment, one or more of
the electrodes have rotational symmetry and reflection symmetry,
where the rotational symmetry is X-fold, and X is 5, 6, 7, 8, 9, 10
or more. In a further embodiment, the rotationally symmetrical
overlapping electrodes are arranged such that no straight line can
be drawn between two adjacent electrodes without overlapping one or
both of the two adjacent electrodes. The invention also includes
electrodes that are sections of rotationally symmetrical shapes,
such as a quarter or half of a rotationally symmetrical shape. In
some embodiments, the sections are characterized in that the lines
creating the sections generally intersect the center point of the
rotationally symmetrical shape, i.e., like slices of a pie. In
still another embodiment, the overlapping regions of adjacent
rotationally symmetrical electrodes generally fit together like
pieces of a puzzle except that each point along adjacent edges of
adjacent electrodes is separated by a gap from a corresponding
point on the other of the adjacent electrodes.
[0062] FIG. 6 illustrates a side view of a droplet actuator 600.
Droplet actuator 600 includes a top substrate 610 and a bottom
substrate 614 that are arranged in a generally parallel fashion.
Top substrate 610 and bottom substrate 614 are separated to provide
a gap 618 therebetween. Both top substrate 610 and bottom substrate
614 include a set of electrodes 622, e.g., droplet operations
electrodes. In the embodiment shown, both substrates include an
insulator layer 626 associated therewith, which forms a droplet
operations surface 627. Insulator layers 626 may be formed of any
dielectric material, such as polyimide. Reference electrodes are
not shown. A hydrophobic coating (not shown) may also be
present.
[0063] In one embodiment, droplet operations electrodes 622 include
at least a subset of electrodes 622 associated with top substrate
610 which are substantially congruent (having substantially the
same size and shape) with and/or in registration (being
substantially aligned on opposite plates) with a subset of
electrodes 622 associated with bottom substrate 614 (e.g., a
perpendicular line passing through the center-point of an electrode
622 on the bottom substrate 614 would approximately pass through
the center point of a corresponding electrode 622 on the top
substrate 610).
[0064] In one embodiment, gap 618 is sufficiently wide that: (a)
one or more droplets 630 having a footprint which is from about 1
to about 5 times the size of the footprint of a droplet operations
electrode 622 can be subjected to droplet operations on surface 627
of top substrate 610 without contacting surface 627 of bottom
substrate 614; and (b) one or more droplets 634 having a footprint
which is from about 1 to about 5 times the size of the footprint of
a droplet operations electrode 622 can be subjected to droplet
operations on surface 627 of bottom substrate 614 without
contacting surface 627 of top substrate 610.
[0065] In this embodiment, droplets may be subjected to droplet
operations along both substrates (top and bottom). In one
embodiment, droplets may be merged by bringing a droplet on one
surface into contact with a droplet on the other surface.
[0066] Droplet actuator cartridges of the invention may in various
embodiments include fluidic inputs, on-chip reservoirs, droplet
generation units and droplet pathways for transport, mixing, and
incubation.
[0067] The fluidic input port provides an interface between the
exterior and interior of the droplet actuator. The design of the
fluidic input port is challenging due to the discrepancy in the
scales of real world samples (microliters-milliliters) and the
lab-on-a-chip (sub-microliter). If oil is used as the filler fluid
in the droplet actuator gap, there is also the possibility of
introducing air bubbles during liquid injection. The dimensions of
the fluidic input may be selected to ensure that the liquid is
stable in the reservoirs and does not spontaneously flow back to
the loading port after loading. The entrapment of air as bubbles in
the filler fluid should be completely avoided or minimized during
the loading process.
[0068] In some embodiments the fluidic input port is designed for
manual loading of the reservoirs using a pipette through a
substrate of the droplet actuator. The sample (or reagent) may, for
example, be injected into the reservoir through a loading opening
in the top substrate. The opening may, for example, be configured
to fit a small volume (<2 .mu.L) pipette tip.
[0069] FIG. 7 illustrates an embodiment in which the loading
opening is connected to the reservoir by a narrow channel of width
w, patterned in the spacer material. The liquid pressure in the
reservoir is on the order of .gamma.(1/R+1/H) where R is the radius
of the reservoir, H is the height of the reservoir and .gamma. is
the interfacial tension of the liquid with the surrounding media.
Since R is typically much greater than h the pressure can be
approximated as .gamma./H. The pressure in the channel connecting
the loading port and the reservoir is .gamma.(1/w+1/H). If w is on
the order of H then the pressure in the channel is 2.gamma./H which
is twice the pressure in the reservoir. Therefore by choosing w to
be close to H the liquid is forced to remain in the reservoir and
not spontaneously flow back into the loading opening. This pressure
difference is initially overcome by the positive displacement
pipetting action, to fill the reservoir with the liquid.
[0070] FIG. 7 also illustrates steps for dispensing a droplet. In
the specific embodiment illustrated, droplet dispensing from an
on-chip reservoir occurs in the following steps. In Step A, the
reservoir electrode is activated. In Step B, a liquid column is
extruded from the reservoir by activating a series of electrodes
adjacent to it. Once the column overlaps the electrode on which the
droplet is to be formed. In Step C, all the remaining electrodes
are deactivated to form a neck in the column. In Step D,
simultaneously or subsequently to Step C, the reservoir electrode
is activated to pull the liquid back causing the neck to break
completely and form a droplet.
[0071] Though simple in principle, the reliability and
repeatability of the dispensing process is affected by several
design and experimental parameters. The design parameters include
the reservoir shape and size, shape and size of the pull-back
electrode, size of the unit electrode (and correspondingly the unit
droplet) and the spacer thickness. In one embodiment, the design
parameters may be established as follows: The electrode size may be
fixed, e.g., at about 500 .mu.m, and most of the other design
parameters were chosen using this as the starting point. Droplet
dispensing for a water-silicone oil system may be suitably
conducted using a droplet aspect ratio (diameter/height) greater
than 5 and a water-air system may be suitably conducted using a an
aspect ratio greater than 10. Thus, given an approximately 500
.mu.m electrode size, the spacer thickness may be about 100 .mu.m
for a nominal droplet diameter of 500 .mu.m. For this electrode
size and spacer thickness combination the unit droplet volume is
expected to be between about 25 and 50 nL. Larger aspect ratios
caused droplets to split easily even while transporting. As a rule
of thumb, an aspect ratio between about 4 and about 6 is most
optimal for droplet transport, dispensing and splitting for an
electrowetting system in silicone oil.
[0072] The reservoir size is essentially determined by the smallest
pipette-loadable volume on the lower end and chip real-estate
concerns on the higher end. In theory, the reservoirs could be made
as large as possible and always filled with a smaller quantity of
liquid as needed. In some embodiments, reservoir capacities may
vary from about 500 to about 1500 nL.
[0073] A tapering pull-back electrode (wider at the dispensing end)
may be employed in some embodiments to ensure that the liquid stays
at the dispensing end of the reservoir as the reservoir is
depleted.
[0074] In addition to the design parameters discussed above there
are additional experimental factors which affect dispensing, and
these include the volume of liquid in the reservoir, the length of
the extruded liquid column and the voltage applied. It is generally
observed that the volume variation is much higher for the last few
droplets generated from a reservoir i.e. when the reservoir is
close to being empty. The length of the extruded column also
determines the volume of a unit droplet. During the necking process
the liquid in the extruded column drains with half the volume going
towards the reservoir and another half towards the droplet.
Therefore the longer the extruded finger the larger the droplet
volume. The volume variation is also larger when the droplet is
formed farther away from the reservoir. The extruded liquid column
also determines the minimum unusable dead volume in the
reservoir.
[0075] The invention provides droplet actuators and associated
systems configured for loading one or more droplet fluids by
displacement of filler fluid. The invention also provides methods
of making and using such droplet actuators.
[0076] In some cases, the droplet fluid loading approach of the
invention relies on displacement of filler fluid in order to move a
droplet fluid from a locus which is exterior to the gap to a locus
which is inside the gap and/or from one portion of the gap to
another. In one embodiment, the droplet fluid loading operation
moves a droplet fluid from a position in which the droplet is not
subject to droplet operations to a locus in which the fluid is
subject to droplet operations. For example, a droplet fluid loading
operation of the invention may be employed to move a droplet fluid
from a locus in which the droplet fluid is not subject to
electrode-mediated droplet operations into a locus in which the
droplet fluid is subject to electrode-mediated droplet operations.
In a specific example, an aliquot of droplet fluid may be
transported into proximity with electrodes configured to dispense
droplets of the droplet fluid, and the electrode arrangement may be
used to dispense such droplets and may further be used to transport
such droplets to downstream droplet operations, e.g. for conducting
an assay.
[0077] Various droplet fluid loading purchase of the invention work
well for any droplet fluid volume, including small droplet fluid
volumes; reduce, preferably entirely eliminate, the possibility of
introducing air into the droplet actuator during loading; and
reduce, preferably entirely eliminate, dead volume of droplet
fluid.
[0078] FIGS. 8A and 8B illustrate a side view and top view (not to
scale), respectively, of a droplet actuator 800. Droplet actuator
800 is configured to make use of negative displacement of filler
fluid for droplet fluid loading. Droplet actuator 800 includes a
top substrate 810 and a bottom substrate 814 arranged to provide a
gap for conducting droplet operations. A reservoir electrode 818
and a set of electrodes 822 (e.g., droplet operations electrodes)
are provided in association with bottom substrate 814. The gap
between top substrate 810 and a bottom substrate 814 is filled with
a volume of filler fluid 824.
[0079] A loading assembly 826 is provided atop top substrate 810,
as illustrated in FIG. 8A. It will be appreciated that top
substrate 810 and loading assembly 826 (as well as other loading
assemblies described herein) may be a single structure comprising
some or all elements of top substrate 810 and loading assembly
826.
[0080] Loading assembly 826 includes a droplet fluid reservoir 830
that substantially aligns with an inlet opening 825 of top
substrate 810. Droplet fluid reservoir 830 is configured to receive
a volume of droplet fluid (not shown), which is to be loaded into
the gap of droplet actuator 800. Loading assembly 826 may also
include a negative pressure opening 834 that substantially aligns
with an outlet opening of top substrate 810. Negative pressure
opening 834 is configured to receive a volume of filler fluid 824
that is displaced during loading of the droplet fluid.
[0081] FIG. 8B illustrates gasket 838 arranged to direct droplet
fluid (not shown) from droplet fluid reservoir 830 toward reservoir
electrode 818 during a fluid loading operation. Reservoir 830 is
located a certain distance from reservoir electrode 818 in order to
hinder or restrain droplet fluid (not shown) from retreating back
into droplet fluid reservoir 830 once loaded into droplet actuator
800. Additional aspects of droplet actuator 800 in use are
described with reference to FIGS. 9A, 9B, and 9C.
[0082] FIG. 9A illustrates a side view of droplet actuator 900 (not
to size) with droplet fluid reservoir 930 being loaded with droplet
fluid. A droplet fluid source 950, such as a pipette or syringe,
may be used to deposit a volume of droplet fluid 954 into droplet
fluid reservoir 930. A negative pressure device 958 (not to size),
such as, but not limited to, a syringe, pipette, or pump, may be
securely fitted to negative pressure opening 934. The size of
negative pressure opening 934 may be selected to couple the opening
to a negative pressure device 958, e.g., the tip of a pipette,
syringe, or other negative pressure device or coupling for a
negative pressure device, such as a capillary tube. Initially,
negative pressure device 958 is in a state of applying little or no
significant negative pressure to filler fluid 924, as illustrated
in FIG. 9A, and droplet fluid 954 is retained in droplet fluid
reservoir 930.
[0083] FIG. 9B illustrates a side view of droplet actuator 900
during a droplet fluid loading operation using negative pressure
device 958. Negative pressure is applied to filler fluid 924 using
negative pressure device 958. Droplet fluid 954 flows from droplet
fluid reservoir 930 through opening 925 (shown in FIG. 9A), into
droplet actuator 900, and toward reservoir electrode 918. The
negative pressure device forces a volume of filler fluid 924 out of
the gap, and the displaced filler fluid is replaced by a volume of
droplet fluid 954. This action continues until a desired volume of
droplet fluid 954 is drawn into sufficient proximity with reservoir
electrode 918 to permit reservoir electrode 918 to be used to
conduct one or more electrode-mediated droplet operations. As
illustrated in FIG. 9C, reservoir electrode 918 may be activated to
induce loaded fluid to move into a locus which is generally atop
the reservoir electrode 918.
[0084] FIG. 9C illustrates a side view of droplet actuator 900
following the droplet fluid loading operation. A slug of droplet
fluid 954 is positioned atop reservoir electrode 918. A volume of
filler fluid 924 has been removed from the gap due to the action of
negative pressure device 958.
[0085] FIG. 10A illustrates a side view (not to scale) of a droplet
actuator 1000 that makes use of negative displacement for droplet
fluid loading. Droplet actuator 1000 is substantially the same as
droplet actuator 1000 that is described in FIG. 8, except that the
negative pressure opening and the negative pressure device of
loading assembly 1026 is constituted by a threaded negative
pressure opening 1010 that has a screw 1014 therein. The action of
backing screw 1014 out of threaded negative pressure opening 1010
creates negative pressure (i.e., vacuum pressure). FIG. 10A
illustrates screw 1014 substantially fully engaged within threaded
negative pressure opening 1010 and a volume of droplet fluid 1054
present in droplet fluid reservoir 1030. Screw 1014 may be backed
out of threaded negative pressure opening 1010 to force a volume of
filler fluid 1024 out of the gap. The displaced filler fluid 1024
is replaced by droplet fluid 1054 as it is drawn into droplet
actuator 1000.
[0086] FIG. 10B illustrates a side view of droplet actuator 1000
with the droplet fluid loading operation complete. More
specifically, FIG. 10B illustrates a slug of droplet fluid 1054
atop reservoir electrode 1018 and a volume of filler fluid 1024
that is present within threaded negative pressure opening 1010 due
to the action of backing out screw 1014, which creates a negative
pressure (i.e., vacuum pressure).
[0087] Referring again to FIG. 8, loading assembly 1026, which may
include any of the active negative pressure mechanisms, may be
permanently attached to the droplet actuator or, alternatively, may
be attached to the droplet actuator during droplet fluid loading
only and then removed.
[0088] FIGS. 11A illustrates a side view (not to scale) of a
droplet actuator 1100. Droplet actuator 1100 is substantially the
same as the droplet actuator that is described in FIGS. 8 and 9,
except that the negative pressure opening and the negative pressure
device of loading assembly 1126 is replaced with a negative
pressure opening 1110 that has a septum 1114 therein. Septum 1114
is configured to seal negative pressure opening 1110 and is formed
of a material that is suitable for sealing, that is resistant to
the filler fluid, and that may be easily punctured. For example,
septum 1114 may be formed of any rubbery material, such as
elastomer material. Atop septum 1114 is an absorbent material 1118,
which may be any material that is suitable for absorbing filler
fluid 1124 and that may be easily punctured. For example, absorbent
material 1118 may be a sponge material or foam material.
[0089] In operation, a volume of droplet fluid 1154 is deposited
into droplet fluid reservoir 1130, as illustrated in FIG. 11A.
Subsequently, septum 1114 and absorbent material 1118 are punctured
in a manner to form a capillary 1122 between filler fluid 1124 in
the gap of droplet actuator 1100 and absorbent material 1118, as
illustrated in FIG. 11B. In this way, due to negative pressure
created by capillary 1122, which is displacing filler fluid 1124
into absorbent material 1118, droplet fluid 1154 displaces filler
fluid 1124 as it is pulled into sufficient proximity with reservoir
electrode 1118 such that reservoir electrode 1118 may be employed
to conduct one or more droplet operations using droplet fluid
1154.
[0090] FIG. 11B illustrates a side view of droplet actuator 1100
with the droplet fluid loading operation complete. More
specifically, FIG. 11B illustrates a slug of droplet fluid 1154
atop reservoir electrode 1118 and a volume of filler fluid 1124
that is present within capillary 1122 and absorbent material 1118
due to the creation of negative pressure when septum 1114 and
absorbent material 1118 are punctured.
[0091] Referring again to FIG. 11B, droplet fluid reservoir 1130
has a diameter D, the gap of droplet actuator 1100 has a height h,
and capillary 1122 has a diameter d. In order to create the desired
pressure differentials along droplet actuator 1100 that best
encourages fluid flow from droplet fluid reservoir 1130 to
capillary 1122, D>h>d.
[0092] FIG. 12A illustrates a side view (not to scale) of a droplet
actuator 1200. Droplet actuator 1200 makes use of a passive method
of filler fluid displacement for droplet fluid loading. Droplet
actuator 1200 is substantially the same as the droplet actuator
that is described in FIGS. 8 and 9, except that the negative
pressure opening of loading assembly 1226 that has the negative
pressure device installed therein is replaced with a capillary 1210
and no mechanism installed therein.
[0093] Additionally, droplet fluid reservoir 1230 has a diameter D,
the gap of droplet actuator 1200 has a height h, and capillary 1210
has a diameter d. In order to create the desired pressure
differentials along droplet actuator 1200 that promote fluid flow
by capillary forces from droplet fluid reservoir 1230 into
capillary 1210, D>h>d.
[0094] The capillary 1210 is sealed using tape for example (not
shown) before fluid loading and air is trapped within the
capillary. In operation, when a volume of droplet fluid 1254 is
loaded into droplet fluid reservoir 1230, and the seal is removed,
the capillary action of capillary 1210 pulls filler fluid 1224
therein and creates a negative pressure that allows a slug of
droplet fluid 1254 to move into droplet actuator 1200 and displace
filler fluid 1224.
[0095] FIG. 12B illustrates a side view of droplet actuator 1200
with the droplet fluid loading operation complete. More
specifically, FIG. 12B illustrates a slug of droplet fluid 1254
atop reservoir electrode 1218 and a volume of filler fluid 1224
that is present within capillary 1210 due to the creation of
negative pressure via capillary 1210.
[0096] FIGS. 13A and 13B illustrate a side view and top view (not
to scale), respectively, of a droplet actuator 1300. Droplet
actuator 1300 is formed of a top substrate 1310 and a bottom
substrate 1314, with a gap therebetween. A reservoir electrode 1318
and a set of electrodes 1322 (e.g., droplet operations electrodes)
are provided on bottom substrate 1314. The gap between top
substrate 1310 and bottom substrate 1314 is filled with a volume of
filler fluid 1326. Additionally, top substrate 1310 includes a
fluid reservoir 1330 that substantially aligns with an inlet
opening of top substrate 1310, which is near reservoir electrode
1318. Fluid reservoir 1330 is configured to receive a volume of
droplet fluid 1334, which is to be loaded into droplet actuator
1300. Top substrate 1310 also includes one or more vent holes 1338,
which is disposed along electrodes 1322 and near a spacer 1342 that
is between top substrate 1310 and bottom substrate 1314.
[0097] Additionally, the one or more vent holes 1338 are sealed by
a seal 1344. In one example, seal 1344 may be a removable seal. In
another example, seal 1344 may be a seal that may be punctured,
such as a seal that is formed of any rubbery material (e.g.,
elastomer material) or foil material. In any case, seal 1344 is
formed of a material that is resistant to the filler fluid.
Furthermore, FIGS. 13A and 13B show a volume of air 1350 that is
trapped is in the gap of droplet actuator 1300, and at the one or
more vent holes 1338.
[0098] In operation, prior to loading filler fluid 1326 into
droplet actuator 1300, the one or more vent holes 1338, which are
negative pressure holes, are sealed via seal 1344. With vent holes
1338 sealed, droplet actuator 1300 is then loaded with filler fluid
1326, which causes a volume of air 1350 to be trapped in the gap,
against spacer 1342 and at vent holes 1338, as illustrated in FIGS.
13A and 13B. Air 1350 is trapped under pressure because there is no
path for venting air 1350 out of droplet actuator 1300. The volume
of air 1350 may be controlled, for example, by the placement of the
one or more vent holes 1338 and/or by the geometry of spacer 1342.
Droplet fluid 1334 is present in fluid reservoir 1330, which is
sealed with seal 1347. Thus, the contents of the droplet actuator
are under pressure. In order to load droplet fluid 1334 into
droplet actuator 1300, seal 1344 is breached (e.g., removed, broken
or punctured) which permits pressurized air 1350 to escape through
vent holes 1338, which causes droplet fluid 1334 to displace filler
fluid 1326 as it flows into the one or more vent holes 1338. This
action pulls a slug of droplet fluid 1334 onto reservoir electrode
1318 (not shown).
[0099] Additionally, fluid reservoir 1330 has a diameter D, the gap
of droplet actuator 1300 has a height h, and vent holes 1338 have a
diameter d. In order to create the desired pressure differentials
along droplet actuator 1300 that best encourage fluid flow from
fluid reservoir 1330 to vent holes 1338, D>h>d.
[0100] Various kinds of pressure sources, positive and/or negative,
may be used to cause dislocation of filler fluid to result in the
desired dislocation or movement of droplet fluid, e.g., vacuum
pump, syringe, pipette, capillary forces, and/or absorbent
materials. For example, negative pressure may be used to dislocate
filler fluid and thereby move a droplet fluid from a locus which is
exterior to the gap to a locus which is inside the gap and/or from
one portion of the gap to another. The pressure source may be
controlled via active and/or passive mechanisms. Displaced filler
fluid may be moved to another locus within the gap and/or
transported out of the gap. In one embodiment, displaced filler
fluid flows out of the gap, while a droplet fluid flows into the
gap and into proximity with a droplet operations electrode.
[0101] For examples of fluids that may be subjected to droplet
operations using the electrode designs and droplet actuator
architectures of the invention, see International Patent
Application No. PCT/US 06/47486, entitled, "Droplet-Based
Biochemistry," filed on Dec. 11, 2006. In some embodiments, the
fluid includes a biological sample, such as whole blood, lymphatic
fluid, serum, plasma, sweat, tear, saliva, sputum, cerebrospinal
fluid, amniotic fluid, seminal fluid, vaginal excretion, serous
fluid, synovial fluid, pericardial fluid, peritoneal fluid, pleural
fluid, transudates, exudates, cystic fluid, bile, urine, gastric
fluid, intestinal fluid, fecal samples, fluidized tissues,
fluidized organisms, biological swabs and biological washes. In
other embodiments, the fluid may be a reagent, such as water,
deionized water, saline solutions, acidic solutions, basic
solutions, detergent solutions and/or buffers. In still other
embodiments, the fluid includes a reagent, such as a reagent for a
biochemical protocol, such as a nucleic acid amplification
protocol, an affinity-based assay protocol, a sequencing protocol,
and/or a protocol for analyses of biological fluids.
[0102] The foregoing detailed description of embodiments refers to
the accompanying drawings, which illustrate specific embodiments of
the invention. Other embodiments having different structures and
operations do not depart from the scope of the present invention.
This specification is divided into sections for the convenience of
the reader only. Headings should not be construed as limiting of
the scope of the invention. The definitions are intended as a part
of the description of the invention. It will be understood that
various details of the present invention may be changed without
departing from the scope of the present invention. Furthermore, the
foregoing description is for the purpose of illustration only, and
not for the purpose of limitation, as the present invention is
defined by the claims as set forth hereinafter.
* * * * *