U.S. patent application number 12/702162 was filed with the patent office on 2010-08-12 for surface tension controlled valves.
This patent application is currently assigned to LIFE TECHNOLOGIES CORPORATION. Invention is credited to Sergey V. Ermakov.
Application Number | 20100200094 12/702162 |
Document ID | / |
Family ID | 42539388 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100200094 |
Kind Code |
A1 |
Ermakov; Sergey V. |
August 12, 2010 |
SURFACE TENSION CONTROLLED VALVES
Abstract
The present teachings relate to surface tension controlled
valves used for handling biological fluids. The valves controlled
by optically actuating an electro-wetting circuit.
Inventors: |
Ermakov; Sergey V.;
(Hayward, CA) |
Correspondence
Address: |
LIFE TECHNOLOGIES CORPORATION;C/O INTELLEVATE
P.O. BOX 52050
MINNEAPOLIS
MN
55402
US
|
Assignee: |
LIFE TECHNOLOGIES
CORPORATION
Carlsbad
CA
|
Family ID: |
42539388 |
Appl. No.: |
12/702162 |
Filed: |
February 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11330360 |
Jan 10, 2006 |
|
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12702162 |
|
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60642828 |
Jan 11, 2005 |
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Current U.S.
Class: |
137/833 |
Current CPC
Class: |
B01J 2219/00367
20130101; B01L 3/502784 20130101; B01J 2219/00722 20130101; B01L
2400/0487 20130101; B01J 2219/0045 20130101; B82Y 30/00 20130101;
B01L 2300/0816 20130101; B01J 2219/00695 20130101; B01L 3/502792
20130101; B01L 2300/0864 20130101; B01L 2300/168 20130101; B01J
19/0046 20130101; F15D 1/00 20130101; B01J 2219/00389 20130101;
B01L 7/52 20130101; B01L 3/50273 20130101; B01L 2400/0409 20130101;
C40B 60/14 20130101; B01J 2219/00448 20130101; F15D 1/06 20130101;
B01J 2219/00441 20130101; B01L 2400/0406 20130101; B01L 3/502738
20130101; B01L 2400/0415 20130101; B01L 2400/06 20130101; Y10T
436/2575 20150115; Y10T 137/206 20150401; Y10T 436/115831 20150115;
Y10T 436/12 20150115; B01J 2219/00675 20130101; C40B 40/06
20130101; B01L 2400/0427 20130101; B01J 2219/00369 20130101; C40B
50/14 20130101; B01L 2400/0688 20130101; B01L 2200/10 20130101;
Y10T 137/2224 20150401; B01J 2219/00439 20130101; B01L 2400/0448
20130101; Y10T 137/0391 20150401; B01L 2200/0605 20130101 |
Class at
Publication: |
137/833 |
International
Class: |
F15C 1/06 20060101
F15C001/06 |
Claims
1-20. (canceled)
21. A valving system comprising a first insulating layer; a second
insulating layer; a channel located between the first insulating
layer and the second insulating layer; a valve connected to the
channel, the valve comprising an internal volume an insulating
layer defining the internal volume and configured to be resistant
to the flow; a photoconductive material located adjacent to the
insulating layer; one electrode located adjacent to the valve; a
power source in communication with the electrode and configured to
activate the electrode, wherein the channel is continuous with the
internal volume of the valve.
22. The system according to claim 21, further comprising a
conductive layer located between the insulating layer and the
photoconductive material.
23. The system according to claim 21, wherein the channel is
connected to at least one reservoir.
24. The system according to claim 24, wherein said reservoir is
chosen from wells and channels.
25. The system according to claims 21 wherein the channel is
connected to at least a first reservoir and a second reservoir
26. The system according to claim 25, wherein the valving system is
configured to control the flow of the liquid from the first
reservoir to the second reservoir.
27. The system according to claim 21, wherein the insulating layer
comprises a hydrophobic material.
28. A device for fluid handling comprising: a valve comprising an
internal volume, the valve configured for light activation; a
channel located between a first insulating layer and a second
insulating layer wherein the channel is connected to the internal
volume of the valve; an insulating layer located on at least a
portion of the valve internal surface, wherein the insulating layer
is configured to be resistant to the flow of a biological liquid; a
photoconductive material located adjacent to the insulating layer;
one electrode electrically coupled to the photoconductive material;
a power source electrically coupled to the electrode, wherein the
power source is configured to provide an electrical potential
difference across the insulating layer; and a light source
configured to activate the photoconductive material to provide an
electrical potential difference across the insulating layer,
wherein the electrical potential difference is configured to reduce
the resistance of the insulating layer to the flow of the
biological liquid.
29. The device according to claim 28, wherein the light source is a
collimated light source.
30. The device according to claim 29, wherein the collimated light
source is at least one of lasers, lamps, or light emitting
diodes.
31. The device according to claim 28, wherein the device comprises
an array of mirrors, wherein the light source is directed by the
array of microfabricated mirrors.
32. The device according to claim 28, wherein the light source is a
laser beam.
33. The device according to claim 32, comprising a galvo-mirror,
wherein the laser beam is directed by the galvo-mirror.
34. The device of claim 28, wherein the light source is configured
to direct a beam of light to the photoconductive material
substantially axially.
35. The device according to claim 28, wherein the channel comprises
a waveguide for the light.
36. The device according to claim 35, wherein the channel comprises
walls and wherein the walls of the channel are the waveguide.
37. The device according to claim 35, wherein the channel is the
waveguide.
38. A device for fluid handling, the device comprising: means for
providing a fluid to a valving means wherein the valving means
includes an insulative layer resistant to the flow of a fluid;
means for electrowetting the valving means to reduce the resistance
of the insulating layer to the flow of the biological liquid
wherein the means for electrowetting the valving means includes a
layer of photoconductive material connected to the insulative
layer; and means for optically activating the means for
electrowetting.
39. The device according to claim 38, wherein the means for
optically activating comprises means for selectively positioning
light onto a portion of the valving means.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/330,360, filed Jan. 10, 2006, which claims a priority
benefit under 35 U.S.C. .sctn.119(e) from U.S. Patent Application
No. 60/642,828, filed Jan. 11, 2005, which is incorporated herein
by reference.
FIELD
[0002] The present teachings relate to surface tension controlled
valves, which may be suitable for controlling liquid flow.
INTRODUCTION
[0003] One of the challenges encountered in devices, for example,
microfluidic devices designed for high throughput operations, is
effective control of fluid flow. It may be difficult to
individually and independently control fluid flow in thousands of
microchannels without requiring fabrication of sophisticated
valving systems, which may substantially increase the cost of
manufacturing microfluidic devices. Addressing and actuating
thousands of individual valves in a device may be very complex. It
could be beneficial to devise a method for manipulating fluid flow
inside a device, for example a microfluidic device, with great
flexibility and, more specifically, employ valves that can be
easily and independently actuated. The use of such valves could
make it practical to implement a variety of devices, such as
lab-on-a-chip devices.
SUMMARY
[0004] In various embodiments, the present teachings can provide a
surface tension controlled valving system for biological fluid,
including a channel connected to an internal volume for the valving
system, wherein the internal volume is bound by an insulating layer
resistant to the flow of the biological liquid, and wherein the
channel is not resistant to the flow of the biological liquid, a
photoconductive material coupled to the insulating layer, an
electrode coupled to the photoconductive material and configured to
electrically couple with the insulating layer through the
photoconductive material, and a power source electrically coupled
to the electrode, wherein the power source is configured to provide
an electrical potential difference between the photoconductive
material and the biological fluid, wherein the photoconductive
material is activatable by directed light to provide the electrical
potential difference between the insulating layer and the
biological fluid, and wherein the electrical potential difference
is configured to reduce the resistance of the insulating layer to
the flow of the biological liquid.
[0005] In various embodiments, the present teachings can provide a
device for biological fluid handling, including a valve configured
for light activation, a channel connected to an internal volume of
the valve, wherein the internal volume is bound by an insulating
layer resistant to the flow of the biological liquid, and wherein
the channel is not resistant to the flow of the biological liquid,
a photoconductive material coupled to the insulating layer, an
electrode coupled to the photoconductive material and configured to
electrically couple with the insulating layer through the
photoconductive material, and a power source electrically coupled
to the electrode, wherein the power source is configured to provide
an electrical potential difference between the photoconductive
material and the biological fluid, a light source adapted to
activate the photoconductive material thereby providing the
electrical potential difference between the insulating layer and
the biological fluid, wherein the electrical potential difference
is configured to reduce the resistance of the insulating layer to
the flow of the biological liquid.
[0006] In various embodiments, the present teachings can provide a
device for biological fluid handling, including means for providing
the biological fluid to a valving means, wherein the means for
providing the biological fluid is not resistant to the flow of the
biological liquid, and wherein the valving means is resistant to
the flow of the biological liquid, means for electrowetting the
valving means to reduce the resistance of the valving means to the
flow of the biological liquid, and means for optically activating
the means for electrowetting.
[0007] It is to be understood that both the foregoing general
description and the following description of various embodiments
are exemplary and explanatory only and are not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate various
embodiments. In the drawings,
[0009] FIG. 1 illustrates a channel connecting two reservoirs
according to the present teachings.
[0010] FIGS. 2A & 2B illustrate the principle behind surface
tension controlled valves according to the present teachings.
[0011] FIG. 3 illustrates movement of a liquid by
electrowetting.
[0012] FIG. 4A illustrates a surface tension controlled valve
closed to the flow of a liquid according to the present
teachings.
[0013] FIG. 4B illustrates a surface tension controlled valve
permitting the flow of a liquid according to the present
teachings.
[0014] FIG. 5 illustrates movement of a liquid by
opto-electrowetting.
[0015] FIG. 6 illustrates moving a liquid through a channel via
opto-electrowetting.
[0016] FIGS. 7A-7D illustrates the operation of a light-actuated
surface tension controlled valve according to the present
teachings.
DESCRIPTION OF VARIOUS EMBODIMENTS
[0017] Reference will now be made to various exemplary embodiments,
examples of which are illustrated in the accompanying drawings.
Wherever possible, the same reference numbers are used in the
drawings and the description to refer to the same or like
parts.
[0018] In various embodiments, the surface tension controlled
valves may be operable with any biological liquid that is capable
of being manipulated by electrowetting forces. The term "biological
liquid" as used herein refers to liquid with biomolecules, for
example nucleic acids, peptides, enzymes, cells, etc. Biological
liquids that are electrolytic may be used in the surface tension
controlled valves according the present teachings. The term
"electrolytic" refers to a liquid containing substances dissolved
therein, such as ionic salts, that enable the liquid to conducting
an electric current. By way of non-limiting example, biological
liquids that may be used in the surface tension controlled valves
according to the present teachings can include aqueous liquids,
such as water and buffered saline, as well as non-aqueous fluids
such as dimethylsulfoxide and other non-aqueous solvents. The
biological liquids can include ionic liquids may also be used in
the surface tension controlled valves according to the present
invention. "Ionic liquids" refers to salts that are liquid over a
wide temperature range, including room temperature. The biological
liquid can include various substances, particulate and otherwise.
Such substances may include, for example, surfactants, including
anionic, nonionic, cationic, and amphoteric surfactants. The
composition of the liquid, including the presence of surfactants,
biomolecules, and other substances, may influence the surface
wetting, and thus the contact angle, of the liquid.
[0019] In various embodiments, channels suitable for use in
accordance with the present invention include any volume through
which a liquid may be transported. Suitable channels may be made of
glass, and may optionally be transparent, or at least partially
transparent, when employed in light-actuated surface controlled
tension valves. The channels may be constructed of any material
suitable for containment of a given liquid, for example glass or a
polymeric material. The channels may of any dimension suitable for
manipulating fluids in a desired manner. For example, according to
various embodiments, the length, width and depth of the channels
may range, independently, from 0.1 .mu.m to 10 cm, for example, 10
.mu.m to 1 cm.
[0020] In various embodiments, reservoirs suitable for use in the
surface tension controlled valves disclosed herein include any
space capable of containing a liquid and communicating with at
least one channel. The reservoir may be constructed of any material
capable of holding a liquid, for example glass or a polymer. The
reservoir may be of any shape, for example it may be spherical,
semi-spherical, or conical. The reservoir may be of any size
sufficient to hold the desired volume of liquid. For example, the
reservoir may range in size from 1 nanoliter to 1 liter. In various
embodiments, the reservoir is not associated with an electrode,
i.e., the liquid in the reservoir itself is not adapted to
manipulate a liquid by virtue of a significant electrical potential
difference being applied to that liquid.
[0021] In various embodiments, at least one portion of a surface of
at least one channel is coated with a material that it is
chemically resistant to the flow of liquid through the channel.
Suitable non-limiting examples of such materials include polymer
coatings (e.g., polyamides, polymethylacrylates and their
copolymers), BN and SiN, deposited in accordance with any of the
thin-film deposition techniques known to those of ordinary skill in
the art, and polymer films such as, e.g., Teflon.TM. (trademark for
polytetrafluoroethylene).
[0022] In various embodiments, at least one layer of insulation
material is formed above the electrode. The surface tension
controlled valve may have the insulation layer disposed between the
electrode and the internal volume making up the channel. In one
aspect of the present teachings, the insulation layer includes at
least one layer of silicon oxide and at least one layer of
Teflon.TM. (trademark for polytetrafluoroethylene). The thicknesses
of the two layers may be selected to provide the desired degree of
insulation without, in the case of a light-actuated surface tension
controlled valve, overly impeding the transmission of light.
[0023] In various embodiments, the electrodes used in accordance
with the present disclosure are made from any conductive material
such as, for example, copper, gold, platinum, and conducting
polymers, including polymers that are conducting per se, and
conducting composites containing a non-conducting polymer and a
conducting material such as a metal or a conducting polymer. A
single electrode may be used in the surface tension controlled
valves disclosed herein, and multiple electrodes, for example an
array of electrodes, may also be used. In various embodiments, the
electrode may be transparent, for example, may be formed of
transparent indium tin oxide. This permits the passage of light in
accordance with certain embodiments of the light actuated valve,
and also permits visual inspection of the operation of the valve.
In various embodiments, in the case of a light-actuated surface
tension controlled valve, the electrode or array of electrodes is
in electrical contact with a photoconductive material.
[0024] In various embodiments, the photoconductive material used in
the light actuated valves corresponds to a material with a dark
conductivity ranging from 10.sup.5 to 10.sup.12 .OMEGA.cm. The
photoconductive material exhibits relatively low conductivity when
dark, and relatively high conductivity when illuminated by a light
source. In various embodiments, an example of a suitable
photoconductive material is amorphous silicon, which has a dark
conductivity of approximately 10.sup.8 .OMEGA.cm. In various
embodiments, light with a wavelength ranging from 400 nm to 1100 nm
is used to illuminate at least portions of the amorphous silicon.
The light intensity for activating the light actuated surface
tension controlled valve can be low. For example, a light intensity
that may be suitable for switching amorphous silicon is 65
mW/cm.sup.2. The layer of photoconductive material permits optical
control of an electrical potential difference across a
corresponding portion of the channel.
[0025] In various embodiments, the power source may be chosen from
any source suitable for providing a sufficient electrical potential
difference across a liquid in a channel. For example, the power
source is configured to provide an alternating voltage source. The
voltage and frequency characteristics may be chosen according to
the materials used in the surface tension controlled valve and/or a
device in which the valve is situated. The magnitude of the AC
voltage source can vary according to the properties, e.g., the
thickness, of the materials used to construct the surface tension
controlled valve. In various embodiments, the AC voltage source can
supply an electrical potential difference ranging from 10 volts to
several hundred volts, with a frequency ranging from 10 Hz to 500
kHz. In one embodiment, the AC voltage source is coupled to the
surface tension controlled valve with only two leads. In another
embodiment, the AC voltage source is inductively coupled such that
no electrical leads are required.
[0026] In various embodiments, the light actuated surface tension
controlled valves may employ a light source as a means of
illuminating the photoconductive material associated with the
valve. The light source may be chosen based on any light capable of
changing the conductive properties of the photoconductive material.
Suitable light sources include collimated light sources, and may be
chosen from, for example, lamps, for example and arc lamp, lasers,
and light-emitting diodes (LEDs). In various embodiments, the light
source may include one or more light sources. For example, a
surface tension controlled valve and/or a device containing a
surface tension controlled valve may include a first light source
and a second light source. In embodiments including more than one
light source, the light sources may be chosen from any effective
light source. The light source may be directed along at least one
axis of the surface tension controlled valve by at least one
mirror, for example a computer-controlled array of microfabricated
mirrors. In various embodiments, when the light source is a laser
beam, the laser beam may be directed over the surface of the
photoconductive material with a computer-controlled
galvo-mirror.
[0027] In various embodiments, the light from the light source can
be directed to the photosensitive material by the channel itself.
The channel can provide a waveguide to internally reflect and
propagate the light so that it reaches the photosensitive material.
The waveguide can direct a beam of light to the photoconductive
material substantially axially along the length of the channel. In
various embodiments, the channel can be configured to provide a
waveguide for the light. In various embodiments, the walls of the
channel can provide the waveguide by internally reflecting and
propagating the light within the channel wall. The channel walls
can be constructed of substantially transparent material with the
outer surfaces of the transparent material coated with a reflective
material. In various embodiments, the channel itself can be the
waveguide by internally reflecting and propagating the light within
the channel volume whether filled or empty. The inner walls of the
channel can be coated with a reflective material.
[0028] The term "reflective material" as used herein refers to any
material that can reflect a predetermined wavelength of light.
Reflective materials can be a coating, a distinct layer, or a
various components described herein can themselves act as a
reflective materials. Some exemplary reflective materials include,
for example, insulators, such as SiO.sub.2, TiN, SiON;
semiconductor materials, such as silicon, germanium, silicon
germanium, and compound semiconductors; polymers, such as
Teflon.RTM., Teflon.RTM. AF; an organic-inorganic hybrid material
as disclosed above, or any other reflective material that will be
known to one of ordinary skill in the art.
[0029] In various embodiments, the surface tension controlled
valves disclosed herein can be used in a variety of applications.
For example, the valves can be used to move one or more droplets or
combine two or more droplets in a device used for biological
synthesis, biological monitoring, or biological screening. In
various embodiments, the surface tension controlled valves
disclosed herein may be used in microdevices designed for one or
more of PCR, ligase chain reactions, antibody binding reaction,
oligonucleotide ligations assays, and hybridization assays.
[0030] The term "device" as used herein refers to a device that can
be used in any number of biological processes involving
microfluidics, e.g. microscale amounts, of fluid or larger scale.
Generally, microfluidics involves handling volumes of one
microliter or less. Features contained in microfluidic devices
typically have millimeter to submicrometer dimensions, and may be
adapted to the specific use of the microfluidic device.
[0031] In various embodiments, individual fluid control in a
device, for example a microfluidic device, can be accomplished with
a surface tension controlled valve. Referring to FIG. 1, a surface
tension controlled valve 5 in its simplest implementation includes
a channel 30, a portion 20 of the channel is initially resistant to
the flow of a liquid (e.g., is hydrophobic in the case of an
aqueous liquid) from the internal volume of surface tension
controlled valve 5. As illustrated in FIG. 1, a valve 5 may control
fluid flow through channel 30 between reservoir 10 and reservoir
40. The surface tension of the liquid, in combination with the
resistance of the surface of at least a portion of channel 30 to
the flow of the liquid, prevents its flow from reservoir 40 to
reservoir 10. Surface tension controlled valve exploits the fact
that under certain circumstances the surface tension of the liquid
changes, and that change in turn can trigger a movement of that
liquid. Examples of such circumstances that can change the surface
tension may include applied electric field (electric field),
applied electric field and light (opto-electrowetting), local
increase in temperature, and the like.
[0032] If the surface of a channel is resistant to the flow of a
liquid, e.g. is hydrophobic, some additional force or pressure is
required to push the liquid through the hydrophobic part of the
channel. With reference to FIG. 2A, this principle may be used in
hydrophobic valves when, for instance, the first liquid 50 under
certain pressure P.sub.1 can flow through channel 40 but not
channel 30 filled with second liquid 60 (the second liquid could
include a gas or be a gas) under pressure P.sub.2 and separated by
a surface 20 that is resistant to the flow of the first liquid
(e.g., the surface is hydrophobic in the case of an aqueous first
liquid). If the pressure difference across the valve exceeds a
certain threshold pressure .delta.P.sub.Threshold (where
P.sub.Threshold=P.sub.1-P.sub.2), the resistance of surface 20 to
the flow of first liquid 1 can be overcome and the first liquid can
flow into the channel 30 (FIG. 2B).
[0033] In various embodiments, a number of techniques are provided
for making the pressure difference across the valve exceed a
threshold pressure, thereby allowing the passage of a liquid. One
technique uses electric fields to effect fluid movement by relying
on the ability of electric fields to change the contact angle of
the fluid on a surface that is initially resistant to the flow of a
liquid. When an electric field gradient is applied to a droplet on
a fluid-transporting surface, different contact angles are formed
between leading and receding surfaces of the droplet with respect
to the fluid transporting surface. This imbalance in surface
tension forces will produce a net force that moves the droplet. For
example, in the case of a polar liquid droplet, such as a droplet
of an aqueous liquid, the application of an electric potential
difference across the liquid-solid interface reduces the contact
angle, thereby effectively making the surface more hydrophilic. In
various embodiments, the electrical potential difference effecting
the hydrophilic-hydrophobic conversion are controlled by closing a
circuit to at least one electrode arranged on at least one side of
a channel making up the surface tension controlled valve.
[0034] The term "contact angle" describes the angle formed as a
result of contact between a fluid and a solid surface. It reflects
the interfacial affinity between the fluid and the solid surface,
i.e., the wettability of the surface with respect to the fluid. The
contact angle is inversely correlated with interfacial affinity.
When the fluid is in direct contact with the solid surface, the
contact angle is at least 0.degree. but less than 180.degree.. A
contact angle of 180.degree. or greater indicates that the fluid is
not in direct contact with the solid surface. In such a case, the
fluid may directly contact the surface through an interposing
fluid, or may be levitated from the solid surface. By way of
illustration, a highly hydrophilic surface may form a low angle,
e.g., 1.degree., with respect to water droplets. Similarly, a
highly hydrophobic surface may form a high contact angle, such as
179.degree., with respect to water.
[0035] In various embodiments, one way to alter the surface tension
of a liquid in a surface controlled tension valve is by applying an
electric field. An exemplary embodiment is shown in FIG. 3. An
electrode 70 is embedded below a surface of an insulation layer 80,
and a droplet of a polar liquid 90 is disposed in the channel. The
droplet 90 forms a contact angle .THETA. with the surface of the
insulation layer 80. A power source 100 is configured to apply an
electrical potential difference between the liquid droplet 90 and
the electrode 70. When the circuit including the electrode, power
source, and the liquid droplet 90 is closed and the electrical
potential difference is applied, different contact angles .THETA.
are formed between leading and receding surfaces of the droplet
with respect to the surface 80. This imbalance in surface tension
forces produces a net force and moves the droplet to the position
indicated by the broken line.
[0036] In various embodiments, and as shown in FIG. 3, the top side
of the electrode may be insulated from the liquid droplet by an
insulation layer 80. In a microfluidic device, each electrode (and
potentially each surface tension controlled valve) suitably
contains a way of independent electrical addressing/connection,
which may be accomplished by, for example, disposing a printed
circuit at the bottom of the chip.
[0037] In various embodiments, one aspect of a surface tension
controlled valve in accordance with the present invention is
illustrated in FIG. 4A. Reservoir 40 contains a liquid 50 that
flows into, but not past, a portion of channel 30 that is resistant
to the flow of the liquid. An electrode 70 and insulator 80 are
positioned along one wall of channel 30, which channel communicates
with reservoir 10. A power source and electro-wetting circuit 100
is configured to apply an electrical potential difference across at
least that portion of the channel 30 that is resistant to the flow
of the liquid 50. Absent the presence of the electrical potential
difference, or any other surface tension-breaking source, the
liquid will not flow past that portion of channel 30 because the
liquid does not exceed a certain threshold pressure necessary to
break the surface tension of the liquid.
[0038] In various embodiments, FIG. 4B illustrates the operation of
the surface tension controlled valve when the circuit 100 is closed
and an electrical potential difference exists between electrode 70
and the liquid 50 in channel 30. The applied electric field changes
the contact angle of the edge of the liquid leading into channel
30, thereby breaking the surface tension. When the power source
generates an electrical potential difference, the imbalance in
surface tension between the leading and receding edges of the
liquid produces a net force, which causes movement of the liquid.
The liquid is then permitted to flow through channel 30, past the
portion of the channel initially resistant to the flow of the
liquid, and into reservoir 10. In various embodiments, opening the
circuit and shutting off the electric field can stop the flow of
the liquid through channel 10.
[0039] In various embodiments, the electric circuit may be
activated using light. One implementation of this is shown in FIG.
5, wherein a layer of photoconductive material 160 is added between
the embedded electrode 70 (which is coupled to insulation layer 80)
and electro-wetting circuit 100. In various embodiments, electrode
70 can be positioned between photoconductive material 160 and
insulator 80. In various embodiments, a conductive layer (not
shown) can be positioned between photoconductive material 160 and
insulator 80. A droplet 90 of a liquid forms a contact angle
.THETA. with the surface upon which it rests. Although the power
source may be providing a current, the electro-wetting circuit will
not close unless the photoconductive material is illuminated with
light. Only then will the circuit close, enabling an electrical
potential difference to flow between the electrode 70 and the
liquid droplet 90.
[0040] FIG. 6 illustrates a channel 130 created by an internal
volume between insulating layers 80. The topside of a channel 110
is sufficiently transparent to allow a light beam 120 to pass
through the channel 110 and to a photoconductive layer 160, which
contains an array of electrodes 70. When illuminated by light beam
120, the conductivity of the illuminated portion of the
photoconductive layer 160 changes significantly, thus allowing the
circuit 100 to close between the electrodes 70 and the liquid
droplet 90. More specifically, the portion of the photoconductive
material that is illuminated by a beam of light is capable of
transmitting a higher electric field intensity than a portion of
the photoconductive layer that is not illuminated. The applied
potential difference makes the surface less resistant to the flow
of the liquid droplet, e.g., more hydrophilic in the case of an
aqueous liquid. The contact angle of the liquid changes, and the
liquid propagates along the channel.
[0041] In various embodiments, biological fluid-handling can be
provided by utilizing the principles described above for a valve
configured for light activation. A channel connected to section 20
that forms an internal volume of the valve. The internal volume of
the valve is bound by an insulating layer resistant to the flow of
the biological liquid. The channel is not resistant to the flow of
the biological liquid. The photoconductive material can be coupled
to the insulating layer. The electrode that forms the
electro-wetting circuit can be coupled to the photoconductive
material and configured to electrically couple with the insulating
layer through the photoconductive material when the photoconductive
material is activated by light. The power source can be
electrically coupled to the electrode. The power source is
configured to provide an electrical potential difference across the
insulting layer capable of changing the wettability of the
insulting material. The light source can be configured to activate
the photoconductive material thereby providing the electrical
potential difference between the insulating layer and the
biological fluid. The amount of electrical potential difference is
configured to reduce the resistance of the insulating layer to the
flow of the biological liquid.
[0042] In various embodiments, the light beam 120 is capable of
moving, e.g., being directed along the length of the channel 130.
Such movement may be possible by the use of any device capable of
moving a beam of light such as, by way of non-limiting example, a
galvo-mirror known in the art of laser etching or an array of
microfabricated mirrors known in the art of digital light
projection. As the light beam is directed along the length of
channel 130, the illuminated portions of the photoconductive
material close the circuit between the respective electrode and the
liquid droplet 90. The contact angle of the leading edge 140 of the
droplet changes to a different contact angle from the receding edge
150, an imbalance in surface tension results, and the droplet thus
propogates in the direction of the beam of light.
[0043] That same principle is used to construct a light-actuated
valve (FIGS. 7A-7D). In normal conditions (no light) the valve is
closed, because the liquid in channel 40 has not exceeded a
threshold pressure such that it can pass the portion 20 of channel
30 that is resistant to the flow of the liquid 50 (FIG. 7A).
Portion 20 can include multi-layers 25 that can include an
insulator, an electrode, and a photosensitive layer as described
above. When the light beam 120 illuminates and activates the
electro-wetting circuit formed in the area where liquid 50 contacts
surface 20, the surface becomes less resistant to the flow of the
liquid 50, and the liquid moves into the channel 30 (FIG. 7B). The
beam of light 120 then shifts toward the channel 30 followed by the
liquid (FIG. 7C). Once the light 120 moves across and above surface
20, and part of surface 20 is not illuminated anymore, some liquid
will break apart from the liquid in channel 40, and after the light
is switched off, that liquid will be displaced into channel 30
(FIG. 7D).
[0044] For the purposes of this specification and appended claims,
unless otherwise indicated, all numbers expressing quantities,
percentages or proportions, and other numerical values used in the
specification and claims, are to be understood as being modified in
all instances by the term "about." Accordingly, unless indicated to
the contrary, the numerical parameters set forth in the following
specification and attached claims are approximations that may vary
depending upon the desired properties sought to be obtained by the
present invention. At the very least, and not as an attempt to
limit the application of the doctrine of equivalents to the scope
of the claims, each numerical parameter should at least be
construed in light of the number of reported significant digits and
by applying ordinary rounding techniques.
[0045] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical value, however,
inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing measurements.
Moreover, all ranges disclosed herein are to be understood to
encompass any and all subranges subsumed therein. For example, a
range of "less than 10" includes any and all subranges between (and
including) the minimum value of zero and the maximum value of 10,
that is, any and all subranges having a minimum value of equal to
or greater than zero and a maximum value of equal to or less than
10, e.g., 1 to 5.
[0046] It is noted that, as used in this specification and the
appended claims, the singular forms "a," "an," and "the," include
plural referents unless expressly and unequivocally limited to one
referent. Thus, for example, reference to "a channel species"
includes two or more different channels. As used herein, the term
"include" and its grammatical variants are intended to be
non-limiting, such that recitation of items in a list is not to the
exclusion of other like items that can be substituted or added to
the listed items.
[0047] It will be apparent to those skilled in the art that various
modifications and variations can be made to various embodiments
described herein without departing from the spirit or scope of the
present teachings. Thus, it is intended that the various
embodiments described herein cover other modifications and
variations within the scope of the appended claims and their
equivalents.
* * * * *