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WO2009046125A2 - Plateforme de pinces optoélectroniques à électrodes flottantes (feoet) pour manipulation optique de gouttelettes immergées dans l'huile - Google Patents

Plateforme de pinces optoélectroniques à électrodes flottantes (feoet) pour manipulation optique de gouttelettes immergées dans l'huile Download PDF

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Publication number
WO2009046125A2
WO2009046125A2 PCT/US2008/078476 US2008078476W WO2009046125A2 WO 2009046125 A2 WO2009046125 A2 WO 2009046125A2 US 2008078476 W US2008078476 W US 2008078476W WO 2009046125 A2 WO2009046125 A2 WO 2009046125A2
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Prior art keywords
droplet
droplets
light
feoet
electric field
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WO2009046125A3 (fr
Inventor
Sungyong Park
Pei-Yu Chiou
Chenlu Pan
Michael A. Teitell
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University of California Berkeley
University of California San Diego UCSD
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University of California Berkeley
University of California San Diego UCSD
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C5/00—Separating dispersed particles from liquids by electrostatic effect
    • B03C5/02—Separators
    • B03C5/022—Non-uniform field separators
    • B03C5/026—Non-uniform field separators using open-gradient differential dielectric separation, i.e. using electrodes of special shapes for non-uniform field creation, e.g. Fluid Integrated Circuit [FIC]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C5/00—Separating dispersed particles from liquids by electrostatic effect
    • B03C5/005—Dielectrophoresis, i.e. dielectric particles migrating towards the region of highest field strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C2201/00—Details of magnetic or electrostatic separation
    • B03C2201/02—Electrostatic separation of liquids from liquids

Definitions

  • Droplet-based microfluidic systems have attracted significant interest for their potential utility in high throughput chemical and biological screening applications.
  • biological and chemical reagents are compartmentalized within an immiscible continuous phase.
  • systems of this nature are able to provide benefits in the ability to rapidly mix reagents, control reaction timing, control interfacial properties, and the ability to synthesize and transport solid reagents and products.
  • Droplet based microfluidic systems using two-phase immiscible flow have demonstrated potential in high-speed diagnosis or chemical synthesis.
  • the droplets immersed in a liquid are typically guided by physical microfluidic channels, whereby active control of individual droplets as desired is extremely difficult.
  • a liquid typically oil
  • the use of physically patterned metal electrodes has been put forth as a means for addressing individual droplets in an open oil medium.
  • the addressing of a large number of droplets with this method involves solving complex wiring and interconnection issues using active addressing circuit matrices and CMOS techniques.
  • the need for this complex circuitry dramatically increases the fabrication cost and is highly unfavorable for chemical and biological experiments that frequently require low cost, disposable platforms for the prevention of cross contamination.
  • OET optoelectronic tweezers
  • the present invention provides a number of methods and apparatus for manipulating aqueous droplets within a fluid medium.
  • Floating electrode optoelectronic tweezers as taught herein, provide a novel optical actuation and addressing mechanism for manipulating aqueous droplets immersed or suspended in electrically insulating or low-conductivity fluid mediums.
  • This optical actuation mechanism enables massively parallel assessment of any desired number (e.g., millions) of individual aqueous droplets immersed in a low conduction medium (e.g., oil) on a low cost substrate, or even a disposable substrate (e.g., silicon coated glass), with optical images patterned by a spatial light modulator, such as a digital micromirror device (DMD) or a liquid crystal display (LCD).
  • a spatial light modulator such as a digital micromirror device (DMD) or a liquid crystal display (LCD).
  • DMD digital micromirror device
  • LCD liquid crystal display
  • the flow control device is preferably modulated in response to programming executable on a computer for carrying out the desired manipulation of droplets.
  • Optical actuation of aqueous droplets is demonstrated in oil medium using a single laser beam according to the instant application. Even using the present proof-of-concept implementations, it has been observed that droplet actuation can be achieved using a light intensity of as low as 1 .6 ⁇ Wlmm 2 .
  • the FEOET platform has the capability to perform manipulations of millions of droplets in parallel with a single light emitting diode or halogen lamp.
  • FEOET including direct optical manipulation on a featureless low cost photosensitive electrode in response to the use of an incoherent light source.
  • FEOET also provides new functionalities that could not be achieved by the use of OET devices.
  • Three of the major advantages of FEOET over OET are as follows. (1 ) FEOET devices enable optical manipulation within an insulating medium like oil. (2) FEOET devices require about 2, 100 times less optical power than the minimum optical power requirement that has ever been demonstrated in OET, which is important when implementing a large optical manipulation platform. In addition, the ability to use low optical power assures less impact to biological constituents and some chemical species. (3) FEOET devices require only one photosensitive electrode and are very compatible with PDMS microfluidic devices fabricated by soft lithography techniques. Consequently, in contrast to OET devices, FEOET devices according to the present invention can be readily integrated with mainstream lab-on-a-chip systems for wide-ranging applications.
  • the FEOET platform according to the present invention can open up numerous potential application areas in the field of microfluidics or lab-on-a- chip systems, especially in systems requiring large scale, multiplexed, dynamic, biological, and chemical analysis and synthesis.
  • the FEOET technology provides a platform that allows massively parallel control of millions of droplets individually on an extremely low cost silicon coated glass substrate in response to dynamically reconfiguring optical images, such as controlled from a typical personal computer.
  • the cost of implementing FEOET and its powerful manipulation capability should be extremely attractive for companies in drug screening, chemical synthesis, and biological diagnostics industries.
  • FEOET field-effect transistor
  • teachings include concepts, device structure, fabrication, numerical simulation, and proof-of-concept demonstration results from the present invention. For example, it is demonstrated that a 44 ⁇ W laser beam with an average intensity of 16.55 ⁇ W jmm 2 is able to transport a 750 ⁇ m oil immersed aqueous droplet at a speed of Q2 ⁇ m/s on a FEOET device. It will be expected that the necessary average intensity may be decreased and droplet speed increased as the teachings herein are refined. In either case, these results indicate that FEOET provides an effective mechanism for massively parallel droplet manipulation.
  • aqueous droplets containing chemical and biochemical contents are manipulated by optical image-patterned virtual electrodes through dielectrophoretic (DEP) forces to perform various droplet manipulation functions including (1 ) continuous 2D transport, (2) droplet merging, (3) and parallel processing of a plurality (e.g., sixteen) of droplets.
  • DEP dielectrophoretic
  • Embodiments of the inventive platform promise a low cost, silicon-coated microfluidic system for large scale, multiplexed droplet-based biochemical analysis.
  • the FEOET is described for light-driven transport of aqueous droplets immersed in electrically insulating oil on a featureless photoconductive glass layer using direct optical images.
  • this section demonstrates a 681 ⁇ m de-ionized water droplet immersed in a corn oil medium which is actuated by a 3.21 ⁇ W laser beam having an average intensity as low as 4.08 ⁇ WJ mm 2 at a maximum speed of 85.1 ⁇ m/s on a FEOET device embodiment.
  • FEOET provides a platform for performing massive parallel droplet manipulation with optical images on low cost, silicon- coated glass.
  • a FEOET device structure is described along with fabrication, working principle, numerical simulations, and operational results.
  • virtual electrodes are induced by illuminations of optical images onto a photosensitive layer to produce non-uniform electric fields from which arise dielectrophoretic (DEP) forces directing light-driven manipulation of aqueous droplets containing chemical and biochemical reagents (constituents).
  • DEP dielectrophoretic
  • These photo-adjustable electromechanical forces enable various droplet manipulation functions, including: (1 ) continuous two- dimensional transport with speeds up to 721 ⁇ mjs , (2) droplet merging and mixing, (3) droplet delivery to wells (or other microstructures and microfluidic devices), and (4) large-scale parallel processing, such as demonstrated by manipulation of sixteen droplets (although the techniques can be scaled to any desired plurality of droplets).
  • this section demonstrates successful detection of enhancement of fluorescent signals for fluo-4 preloaded HeLa cells, achieved by optical manipulation of a thmethylin (TMT) chloride droplet for activation of intracellular calcium [ CaJ + ).
  • TMT thmethylin
  • the FEOET system promises a low-cost silicon-coated microfluidic platform which is simple to fabricate (featureless), and programmable to provide flexible and dynamic addressing of optical image patterns when performing large scale multiplexed droplet-based biological and chemical operations and analyses.
  • the invention is amenable to being embodied in a number of ways, including but not limited to the following descriptions.
  • One embodiment of the invention is an apparatus for manipulating aqueous droplets within a liquid medium, comprising: (a) a photoconducting layer; (b) a chamber upon the photoconducting layer into which a liquid medium and at least one aqueous droplet can be retained; wherein the liquid medium is substantially less conductive than the aqueous droplets; (c) at least two conductive electrodes electrically coupled to the photoconducting layer and separated by at least a portion of the chamber; (d) means for applying a bias voltage across the electrodes; and (e) means for projecting a dynamic 2D light pattern onto the photoconducting layer to form virtual electrodes for manipulating the position of aqueous droplets in response to the electric field established about the 2D light pattern based on the conductivity difference between the aqueous droplets and the surrounding liquid medium; (d)(i) wherein the dynamic 2D light pattern breaks the originally symmetric electric field pattern around the aqueous droplets resulting in a non-zero net diele
  • the apparatus can be implemented within a wide range of manual, semi-automatic and automatic applications.
  • At least one embodiment of the invention includes a computer and programming executable on said computer (e.g., computer executes instructions from a memory coupled to the computer) for controlling the output of the dynamic 2D light pattern(s).
  • a position registration device such as an imaging device (i.e., optical imager, sensor array, or similar), can be coupled to the computer to close the feedback loop so that manipulation operations can be accurately performed as desired without manual direction of droplet manipulation.
  • One embodiment of the invention is a method for manipulating aqueous droplets within a liquid medium, comprising: (a) retaining at least one droplet within a less conductive liquid medium on a photoconductive layer; (b) generating an electric field on the photoconductive layer to induce a balanced dielectrophoretic (DEP) force on the droplets; (c) projecting at least one dynamic 2D light pattern onto the photoconductive layer to alter the electric field of the photoconductive layer based on the conductivity difference between the aqueous droplets and the surrounding less conducting liquid medium, creating a net unbalanced DEP force for moving the droplets; and (d) manipulating of the position of the droplets in response to changing the position of the dynamic 2D light pattern(s).
  • DEP dielectrophoretic
  • An aspect of the invention is a floating electrode optoelectronic tweezers (FEOET) apparatus and method for manipulating droplets.
  • FEOET floating electrode optoelectronic tweezers
  • Another aspect of the invention is a FEOET system in which an electric field is applied across a portion of a chamber, such as across a photoconductive layer.
  • Another aspect of the invention is a FEOET system in which a 2D light pattern is projected onto a photoconductive layer to form virtual electrodes which work in combination with an electric field for trapping and moving the position of one or more droplets.
  • Another aspect of the invention is an FEOET device in which the dielectrophoretic force arises in response to the conductivity difference between the droplets being manipulated and the less conductive liquid medium (e.g., oil, corn oil, and so forth).
  • the less conductive liquid medium e.g., oil, corn oil, and so forth.
  • Another aspect of the invention is a FEOET system which utilizes pairs of optical electrodes in combination, such as diamond shaped patterns, or similar (e.g., oval, trapezoidal, elongate and so forth), to optically manipulate droplet position.
  • Another aspect of the invention is a FEOET system which can be utilized with droplets dispersed in low-conductive and non-conductive fluid mediums.
  • Another aspect of the invention is a FEOET system which can be utilized with droplets dispersed in oil.
  • Another aspect of the invention is a FEOET system which includes at least two electrodes between which at least a portion of a chamber is positioned for retaining a liquid medium and droplets is position.
  • Another aspect of the invention is a FEOET system which utilizes a photoresponsive layer for converting incoming light into an electric field which interacts with the liquid medium and the droplets retained therein.
  • Another aspect of the invention is a FEOET system which allows trapping, translating, and merging aqueous droplets which can be directed to any desired wells or other microfluidic structures.
  • Another aspect of the invention is a FEOET system in which a droplet speed on the order of 0.5mm per second is achieved for a droplet approaching 1 mm in diameter moving through a medium having the viscosity of a corn oil.
  • Another aspect of the invention is a FEOET system in which the 2D light patterns are operable even at low light settings on the order of about
  • Another aspect of the invention is a FEOET system in which the 2D light patterns for controlling manipulation of the droplets can be generated by conventional light projecting devices and displays, as well as by custom light generation devices.
  • Another aspect of the invention is a FEOET system which can perform a wide range of manipulation functions including droplet trapping, positional translation of droplets, droplet merging, droplet mixing, droplet delivery to wells and other microfluidic structures, and other operations to which a droplet must be brought through or delivered to.
  • a still further aspect of the invention is a FEOET system which can be implemented to perform simultaneous manual, semi-automatic, or automatic manipulation of any desired plurality of droplets.
  • FIG. 1 is a cross-section of a floating electrode optoelectronic tweezers
  • FIG. 2 is a depiction of a two-dimensional electrical field in response to light illumination, according to numerical simulation.
  • FIG. 3 is a depiction of a two-dimensional electrical field around two droplets without light illumination, according to numerical simulation.
  • FIG. 4 is a depiction of a two-dimensional electrical field around two droplets in response to light illumination, according to numerical simulation.
  • FIG. 5A-5D is an image sequence of light induced water droplet motion in an oil medium according to an aspect of the present invention, shown at various times during motion. [0045] FIG.
  • FIG. 6A-6E is an image sequence of light induced merging of two water droplets in an oil medium according to an aspect of the present invention, shown at various times leading up to droplet merging.
  • FIG. 7 is a graph of droplet motion over time within a fluid medium in response to different light intensities.
  • FIG. 8 is a perspective view of a floating electrode optoelectronic tweezers (FEOET) according to an embodiment of the present invention.
  • FIG. 9A-9D are schematic illustrations of dielectrophoretic (DEP) forces induced by a circular light spot and virtual electrodes with respect to direction.
  • DEP dielectrophoretic
  • FIG. 10A-10B are graphs of electric field distribution about a droplet positioned with respect to the x direction in response to circular illumination, as determined by numerical simulations according to an aspect of the present invention.
  • FIG. 1 1 A-1 1 B are graphs of electric field distribution about a droplet positioned with respect to the y direction in response to circular illumination, as determined by numerical simulations according to an aspect of the present invention.
  • FIG. 12 is a graph of electric field distribution in response to two closely positioned virtual electrodes as determined by numerical simulations according to an aspect of the present invention.
  • FIG. 13A-13B are graphs of electric field distribution about a droplet positioned with respect to the x direction and virtual electrodes as determined by numerical simulations according to an aspect of the present invention.
  • FIG. 14A-14B are graphs of electric field distribution about a droplet positioned with respect to the y direction and virtual electrodes as determined by numerical simulations according to an aspect of the present invention.
  • FIG. 15 is an illustration of a fabricated FEOET device according to an embodiment of the present invention, this example having a 6 x 6 cm active area and two aluminum electrodes.
  • FIG. 16A-16E is an image sequence of light induced optical manipulation of a water droplet by virtual electrodes according to an aspect of the present invention, shown at various times during the trapping and transport sequence.
  • FIG. 17A-17E is an image sequence of light induced optical merging of water droplets using virtual electrodes according to an aspect of the present invention, shown at various times during the trapping, transport and merge sequence.
  • FIG. 18 is a schematic of a micro well structure according to an aspect of the invention, showing an aqueous droplet being directed to a specific well within an array.
  • FIG. 19A-19H is an image sequence of delivering aqueous droplets to target wells, such as that shown in FIG. 18, according to an aspect of the present invention.
  • FIG. 20A-20D is an image sequence of transporting a desired plurality of aqueous droplets according to an aspect of the present invention, showing droplets being trapped and transported in different directions.
  • FIG. 21A-21 C are graphs of electric field distribution in the a-Si:H layer of an FEOET device according to an aspect of the invention, shown under different conditions.
  • FIG. 22A-22C are graphs of electric field distribution on a droplet surface shown without light illumination.
  • FIG. 23A-23C are graphs of electric field distribution on a droplet surface shown in response to light illumination.
  • FIG. 24A-24D is an image sequence of light activated water droplet motion in an oil medium according to an aspect of the present invention.
  • FIG. 25 is a graph of droplet velocity in response to relative droplet position for different optical intensities.
  • FIG. 26 is a schematic of an FEOET-based microfluidic platform according to an aspect of the present invention, showing transport to an array of cells and merging in response to optical reconfiguration.
  • FIG. 27 is a cross-section of a corner portion of the FEOET-based device shown in FIG. 26.
  • FIG. 28A-28F is an image sequence of two-dimensional optical manipulation of a droplet in response to a projected virtual electrode according to an aspect of the present invention, showing trapping and movement.
  • FIG. 28A-28F is an image sequence of two-dimensional optical manipulation of a droplet in response to a projected virtual electrode according to an aspect of the present invention, showing trapping and movement.
  • FIG. 29A-29E is an image sequence of aqueous droplet delivery to target wells according to an aspect of the present invention.
  • FIG. 30A-30E is an image sequence of aqueous droplet merging and mixing according to an aspect of the present invention.
  • FIG. 31A-31 D are images of fluorescent intensity in response to different chemical loading according to aspects of the present invention.
  • FIG. 32A-32F is an image sequence of aqueous droplet transport into
  • Fluo-4 loaded cells in DMEM/CaCb according to an aspect of the present invention.
  • FIG. 33A-33B are images showing elevated fluorescence of TMT activated HeLa cells according to an aspect of the present invention.
  • OET Optoelectronic tweezers
  • OET devices operate in an ionic medium with a conductivity between 10 ⁇ 3 S/m to 1 S/m (units are Siemens per meter [S/m ] in SI units) but is not able to provide optical modulation of electric fields in electrically insulating biocompatible mediums, having significantly less conductivity (e.g., at least two orders of magnitude less than 10 ⁇ 3 S/m ), such as pure corn oil which has a conductivity around 10 ⁇ 14 S/m or above. It should be noted that typical drinking water has a conductivity of between around .
  • the FEOET device presented here enables, optical manipulation of aqueous droplets in an insulating oil with a low light intensity requirement and promises a powerful platform for parallel manipulation of a large array of oil-immersed aqueous droplets with direct optical images.
  • FIG. 1 illustrates an example embodiment 10 of a FEOET device structure fabricated by applying a photoconductive layer (e.g., amorphous hydrogenated silicon: a-Si:H, such as 0.5 ⁇ m thick) 14 to a light transmissive
  • a photoconductive layer e.g., amorphous hydrogenated silicon: a-Si:H, such as 0.5 ⁇ m thick
  • a photoresponsive material 14 can be utilized comprising other semiconducting materials, wherein the teaching herein is not limited to silicon.
  • electrodes for example n+ doped a-Si:H (e.g., 0.1 ⁇ m ) 16 over which is a conductive electrode, such as aluminum (0.1 ⁇ m Al) 18.
  • a conductive electrode such as aluminum (0.1 ⁇ m Al) 18.
  • An electrical bias voltage is applied at the two edges of this photoconductive electrode, as depicted by the voltage and ground symbols.
  • an open chamber 20 e.g., PDMS
  • a medium such as oil (e.g., corn oil)
  • oil e.g., corn oil
  • aqueous droplets 24 are contained or can be introduced.
  • aqueous droplets 24 are contained or can be introduced.
  • a medium such as oil (e.g., corn oil)
  • means for generating aqueous droplets of a desired composition and size are well known within the art.
  • the oil layer 22 and the photosensitive layer are connected in parallel, instead of the serial connection found within an OET device.
  • the electrical configuration of the FEOET is important toward enabling optical modulation of an electric field in as insulating medium.
  • a-Si:H layers doped and undoped
  • a sufficiently light transmissive substrate e.g., glass
  • DEP dielectrophoresis
  • light may be directed to the FEOET device from either side, wherein the substrate may be opaque to the transmission wavelength of light.
  • light may be applied from both sides as desired, insofar as the light patterns are generated cooperatively.
  • two aluminum electrodes deposited at the two edges of the device are separated by a gap
  • n+ a-Si:H layer is used to interface between the Al electrode and the undoped a-Si:H material, wherein after depositing the metallic electrode the n+ a-Si:H material not covered by the Al electrodes is etched away, such as using a reactive ion etcher (RIE).
  • RIE reactive ion etcher
  • a sufficient bias voltage (e.g., 600 VDC in this example) is applied between the two aluminum electrodes to provide a lateral electric field across the whole device in parallel with both the oil and the a-Si:H layers. It should be appreciated that the amount of bias voltage which constitutes a sufficient bias voltage depends on the size of the area over which manipulation is being performed, the application, and other factors. The bias voltage is sufficient in a given application if it provides a sufficient motive force for the droplets in response to operation of the device.
  • the FEOET system is configured to use the conductivity difference between the aqueous droplets and the surrounding oil. It will be noted that the aqueous droplets are significantly more conductive than the surrounding electrically insulating oil. In response to this difference an electric dipole is induced on each droplet under the application of a lateral electric field.
  • the droplet induces a highly non-uniform electric field around itself, the droplet does not move due to dielectrophoresis (DEP) forces since the symmetric electric field pattern around a droplet results in a zero net force.
  • DEP dielectrophoresis
  • a light beam illuminates the photoconductive undoped a-Si:H layer at the edge of a droplet, it creates a light patterned virtual electrode which decreases the electric field strength at the illuminated site of the droplet. This phenomenon breaks the originally symmetric electric field pattern around a droplet and results in a non-zero net DEP force, which drives the droplet away from the light beam.
  • FIG. 2, FIG. 3 and FIG. 4 illustrate an operating principle of the inventive FEOET devices shown through numerical simulation of the electric field distribution in the oil medium 22.
  • FIG. 2 a cross-section is shown of a photoconductive (photosensitive) material 14 at the bottom with biasing electrodes 18 on each end between which is positioned a chamber for retaining an oil medium 22.
  • Optical illumination on the photosensitive layer creates a virtual electrode that decreases the local electric field near the illuminated spot, as seen just right of the lower center.
  • the illumination is provided in this case by a 70 ⁇ m Gaussian laser beam.
  • the local electric field near the illuminated spot is greatly decreased due to the light-patterned virtual electrode in the a-Si:H layer.
  • a symmetric electric dipole is induced around the droplet in response to the water droplet being more conductive than the insulating oil.
  • the conductivity range of aqueous droplets can vary from about IO A S/m , for pure water, to about 10 S/m in response to the concentration of dissolved electrolyte.
  • an electric dipole can be induced around any droplet insofar as sufficient conductivity difference exists between the medium and the droplet.
  • Lower levels of electrical conductivity in the oil medium generally provide more ideal FEOET operating characteristics, resulting in lowered levels of FEOET power consumption.
  • non-polar liquid media usually have very low conductivity and can be considered as electrical insulators. In general, materials having electrical conductivity on the order of 10 ⁇ 14 S/m are considered insulators.
  • materials having electrical conductivity on the order of 10 ⁇ 14 S/m are considered insulators.
  • DEP dielectrophoretic
  • FIG. 5A-5D depict a demonstration of optically induced droplet manipulation, wherein video snapshots show a water droplet immersed in corn oil being repelled by a light spot as predicted in our simulation.
  • a laser beam (532 nm , 4.35 ⁇ W ) was utilized with a spot size of 2 mm , which successfully drove a 750 ⁇ m droplet at a speed of approximately 1 16 //m/s through the oil medium.
  • FIG. 5A depicts the droplet prior to light application, upon application of the light spot in FIG. 5B, and at 15 and 30 seconds after introducing the light in FIG. 5C and 5D, respectfully.
  • FIG. 6A-6E depicts a demonstration of two droplets driven to merge in response to manipulation by a light beam. The optical power required to drive aqueous droplets on FEOET devices is low.
  • FIG. 6A depicts the droplets prior to light application, upon application of the light spots in FIG. 6B, and at 3 and 6 seconds after introducing the light in FIG. 6C and 6D, respectfully, and finally at merging in FIG. 6E.
  • FIG. 7 depicts droplet position with respect to time for two different light intensities. It will be seen from this graph that useful droplet translation speeds can be obtained at low values of light power. [0091] 1 .4 Conclusions
  • a floating electrode optoelectronic tweezers has been described which enables optical manipulation of aqueous droplets in an electrically insulating oil medium with a light intensity as low as 16.55 ⁇ w/mm 2 on a prototype device.
  • the simple and flexible FEOET device allows droplet manipulation to be implemented even with a simple devices structures, such as using an open oil chamber.
  • the simulation results demonstrate the mechanism of successful movement of an aqueous droplet using a light patterned virtual electrode.
  • the virtual electrode decreases the electric field at the illuminated area to disrupt the originally symmetric field pattern around a droplet.
  • the newly non-symmetric electric field induces a net non-zero DEP force thereby repelling the droplet away from the light beam illumination.
  • Experimental results confirm the simulation results and demonstrate droplet movement, of a 750 ⁇ m droplet, using a laser beam
  • Droplet-based microfluidic systems have the potential for supporting high-throughput and high-speed chemical and biological analysis. Thousands of highly uniform, isolated aqueous droplets containing chemical reagents can be generated in immiscible oil within seconds by flow-focusing devices.
  • droplet-based microfluidic devices A major difficulty associated with a droplet-based microfluidic system is in achieving active control of individual droplets confined in microchannels being driven by a continuous oil flow. It has been shown that multiple droplets can be individually addressed in an open oil chamber using physically patterned electrodes, although complex wiring and interconnection issues arise for addressing numerically large droplet arrays. For example, a microfluidic device integrating a high voltage
  • CMOS driving circuit recently achieved active and parallel droplet control. However, this approach increases the fabrication cost of microfluidic devices, which are often preferred to be disposable.
  • paired electrodes of any shape can be successfully utilized for capturing and positionally translating a droplet.
  • preferred variations utilize paired electrodes which are oval, trapezoidal, elongated and so forth.
  • the use of the 2D manipulation opens up the possibility of massively parallel droplet manipulation on featureless (e.g., containing no physical microfluidic structures, for instance channels and walls, for directing the droplet) fluidic platforms (e.g., silicon coated glass substrate) controlled by using dynamic and reconfigurable optical images.
  • Optically patternable virtual electrodes generate dielectrophoretic (DEP) forces to manipulate aqueous droplets containing chemical and biochemical constituents for performing various microfluidic functions such as two- dimensional transport, droplet merging and parallel processing of a plurality of droplets (e.g., sixteen droplets).
  • DEP dielectrophoretic
  • FIG. 8 illustrates an embodiment of an FEOET 10 device within a system 30.
  • this embodiment is fabricated, as in FIG. 1 , by coating a transparent substrate (e.g., glass wafer) 12 with an undoped a-Si:H layer 14 (e.g., Q.b ⁇ m ) and an n+ doped (0.1 ⁇ m ) region for interconnection.
  • a transparent substrate e.g., glass wafer
  • an undoped a-Si:H layer 14 e.g., Q.b ⁇ m
  • n+ doped (0.1 ⁇ m ) region for interconnection.
  • Two aluminum electrodes 18 with a 6 cm lateral gap are deposited at the two edges of this device by e-beam evaporation and lift-off techniques.
  • the Al electrodes also serve as an etching mask for removing the n+ a-Si:H layer, such as by using a Reactive Ion Etcher (RIE).
  • RIE Reactive Ion Etcher
  • the n+ a-S ' wH layer 16 provides ohmic contacts with the Al electrodes.
  • An open poly- dimethylsiloxana (PDMS) chamber 20 retains the aqueous droplets 24 and immiscible oil (corn oil) 22 as affixed upon the layer of undoped a-Si:H.
  • PDMS poly- dimethylsiloxana
  • a means 34 for projecting patterned light 36 onto the photoresponsive layer 14 provides for the generation of virtual electrodes within the chamber for manipulating the droplets therein.
  • a number of devices can be used for generating the dynamic patterned light, such as conventional light projectors displaying a mask pattern (e.g., monochrome, or alternatively colored patterns providing different intensities), display devices, LCD shutter arrangements, MEMs mirror driven devices and other light manipulation devices as known to those of ordinary skill in the art. These light pattern projective means are not described in detail herein, as the present invention may be implemented using a wide range of such devices.
  • FIG. 8 shows additional peripheral aspects of the invention toward integrating the FEOET 10 into a working system 30.
  • control device such as a computer (e.g., at least one CPU, microcontroller, microprocessor, or similar) 36 is needed to sequence and direct the light patterns being output.
  • An optional user interface 40 is shown coupled to the computer for controlling the operation of the system, in particular when operated in manual, or semi-automatic modes.
  • Computer 36 is shown coupled to memory 38 from which programming is read for execution on computer 36 to dynamically control the operation of the FEOET device, such as by adjusting the light patterns impinging on the photoresponsive area of the FEOET device.
  • Light projection means 32 shown outputting light pattern 34, is shown controlled via computer 36, which can control the pattern, size, intensity, and motion of the light used to manipulate the droplets within the FEOET.
  • the bias voltage to the FEOET can also be optionally controlled by the system, such as via computer 36 generating commands to a programmable power supply (PS) 42.
  • PSD programmable power supply
  • the droplets used in the FEOET can be optionally generated by a droplet generating device (DG) 44, such as controlled by computer 36.
  • DG droplet generating device
  • the FEOET system can be optionally configured with one or more position registration means (sensors) (C) 46, such as an optical sensor array, microscopic camera, or the like, whose inputs are received and image processed by either a separate device or programming operable on computer 36.
  • sensors position registration means
  • C position registration means
  • FIG. 9A-9D illustrate DEP forces induced by a circular light spot string. In the field direction the DEP forces are strong (FIG. 9A), yet are weak in the direction perpendicular to applied field (FIG. 9B). However, DEP forces induced by two diamond shaped virtual electrodes are strong in both parallel and perpendicular directions as seen in FIG. 9C-9D. [00106] However, the extent of DEP forces induced on droplets within the
  • FEOET depend upon the direction of applied electric field.
  • the directional force difference is shown in FIG. 9A-9B. This force difference substantially limits droplet motion to one direction, which could be restrictive in a number of applications.
  • the present invention teaches a method for manipulating droplet position using virtual electrodes, such as trapping a droplet between the gap of two diamond- shaped virtual electrodes as shown in FIG. 9C-9D.
  • virtual electrodes such as trapping a droplet between the gap of two diamond- shaped virtual electrodes as shown in FIG. 9C-9D.
  • FIG. 9C-9D it will be appreciated that not only the electric field but also the shape, intensity and positioning of optical virtual electrodes alter the DEP forces applied to the droplets.
  • the preferred diamond shape of the virtual electrodes provides a number of benefits, in particular with regard to submitting a droplet to the same order of magnitude DEP forces in both directions parallel and perpendicular to the applied field.
  • Electrodes may be utilized in combination having either single or multiple orientations.
  • opposing electrodes may be utilized in both x and y directions upon which electric fields are applied having opposing phases.
  • teachings herein can be modified to implement these variations.
  • Numerical simulations of a three-dimensional electric field distribution in a FEOET chamber and on a droplet surface are performed using a simulation program, for instance COMSOL Multiphysics 3.2 ®.
  • the device is simplified to two layers: a b ⁇ m thick undoped a-Si:H and a 350 ⁇ m thick oil medium.
  • a 100 Volt direct current (DC) bias is applied at the two end planes along the x direction, and a 300 ⁇ m diameter aqueous droplet is loaded in a 1 .4 x 0.8 mm oil chamber.
  • the dark conductivity of the homogeneous a-Si:H layer (amorphous semiconductor) is assumed to be about 10 ⁇ 8 S/m .
  • corn oil is an insulating medium having a typical conductivity lower than about 10 ⁇ 14 S/m .
  • the circular light beam is assumed to have a 200 ⁇ m full width at half maximum (FWHM) spot size and it induces a peak photoconductive of 10 ⁇ S/m in the center.
  • FWHM full width at half maximum
  • the same peak photoconductivity is also assumed in the case of diamond-shaped virtual electrodes with a 200 ⁇ m separation gap.
  • the Maxwell stress tensor has been applied for calculating DEP forces on droplets.
  • FIG. 10A-10B and FIG. 1 1A-1 1 B depict numerical simulations of electric field distributions in response to a circular laser beam illumination both parallel to (x-direction) and perpendicular to (y-direction) the applied electric field.
  • a droplet is shown located 150 ⁇ m away from the center along the x direction.
  • FIG. 10B shows the associated electrical field distribution for FIG. 10A.
  • FIG. 1 1A depicts a droplet located 150 ⁇ m away from the center along the y direction, with FIG. 1 1 B showing the associated electrical field distribution.
  • FIG. 10B perpendicular (FIG. 1 1 B) to the applied electric field, respectively.
  • a circular laser beam illumination is assumed to be a 200 ⁇ m full width at half maximum (FWHM) to create a Gaussian photoconductivity distribution with a peak photoconductive of 10 4 S/m in the center of a laser beam.
  • FWHM full width at half maximum
  • Droplet actuation (positional manipulation) on the FEOET arises from the electrostatic dipole-dipole interactions between the droplet and virtual electrodes. Without light illumination, a droplet-induced dipole generates a symmetrical electric field distribution around a droplet surface, resulting in zero net DEP forces for transporting the droplet.
  • To actuate a droplet one can illuminate a light beam at one edge of a droplet to break this field symmetry around the droplet. As shown in FIG. 10A-1 OB, the electric field at the illumination side is greatly reduced, resulting in net DEP forces moving the droplet away from the light beam.
  • the 0.02 nN force in the y direction arises in response to numerical errors.
  • the transport of droplets in the y direction is not as effective as in the x direction. Illuminating a droplet edge at the direction perpendicular (y direction) to the electric field fails to transport the droplet since the electric field strength difference between the illuminated and non-illuminated sides on the droplet surface is too small as shown in FIG. 1 1 A-1 1 B.
  • the y direction force is 78.8 times smaller than that of the x direction force depicted in FIG. 10A-
  • FIG. 12, FIG. 13A-13B and FIG. 14A-14B collectively illustrate simulation field patterns of a droplet trapped in response to the illumination of two diamond patterns onto the a-Si:H layer previously described.
  • FIG. 12 illustrates electric field distribution induced by two closely positioned diamond- shaped virtual electrodes separated by a 200 ⁇ m gap, in which strong electric fields are created.
  • FIG. 13A depicts a droplet located 150 //m away from the center along the x direction, with FIG. 13B showing the unbalanced e-field pattern in the x direction causing the DEP force to drive and trap the droplet to the right.
  • FIG. 13A depicts a droplet located 150 //m away from the center along the x direction, with FIG. 13B showing the unbalanced e-field pattern in the x direction causing the DEP force to drive and trap the droplet to the right.
  • FIG. 14A depicts a droplet located 150 ⁇ m away from the center along the y direction, with the e-field pattern shown in FIG. 14B which is symmetric in the x direction but asymmetric in the y direction, producing a net DEP force to attract the droplet back to the center.
  • the electric field strength at the gap between these two electrodes is strongly enhanced (FIG. 12).
  • the enhanced electric field can generate DEP forces pulling the droplet back to the center of the gap.
  • DEP force in the x direction is similar to the one in case of a circular laser beam.
  • the DEP force shows a dramatic increase compared to the y direction force in the case of a circular light beam.
  • the y direction force of FIG. 14A-14B is only
  • FIG. 15 illustrates an embodiment 10 of a fabricated FEOET device with a 6 x 6 cm active optical manipulation area.
  • Oil medium 22 is shown in a chamber 20 between two Al electrodes 18 to which a 5 kV bias voltage is applied to power the entire device.
  • the voltage is high in this example, the requisite power consumption of the whole device is only 0.4 ⁇ W in the dark state and less than A mW in the bright state due to the large electrical impedance of the oil and a-Si:H thin film ( ⁇ 10 14 ⁇ in the dark state).
  • amorphous silicon is typically utilized as the photoconductor. However, the electric field is applied differently in the two different devices.
  • the electric field is applied perpendicular to the thin film, resulting in a dark resistance of 10 6 ⁇ for a 1 cm ⁇ 1 cm ⁇ 1 ⁇ m film.
  • the electric field in an FEOET device is applied in the direction parallel to the amorphous silicon thin film, wherein the resulting resistance is approximately 10 14 ⁇ , which is about eight orders of magnitude higher than in the OET.
  • the unique operating properties of the FEOET are not surprising, and in view of which the electric power consumption of the FEOET can be as low as 0.4 ⁇ W even in response to a very high voltage drive.
  • 16A-16E depicts video snapshots of two-dimensional optical manipulation on a FEOET device transporting the droplet in both x and y directions by reconfiguring projected optical images.
  • the image sequence shows manipulation of a 1 .47 ' mm droplet containing the Trypan blue dye.
  • the light and dark circles indicate droplet positions before and after movement.
  • two diamond-shaped virtual electrodes create a strong electric field between the gap to trap the droplet shown.
  • FIG. 16C the trapped droplet is transported to the right hand side along the electric field (e-field) direction.
  • the droplet is driven to the top side perpendicular to e- field direction, while in FIG. 16E the droplet is shown being moved to the left hand side again.
  • FIG. 17A-17H illustrate video snapshots of two 1 mm droplets containing different color dyes (e.g., yellow and green food coloring dyes) which are transported and merged.
  • the droplets are shown in an initial position with the voltage off. Droplet trapping is then seen in FIG. 17B, with the diamond pattern pairs being moved relative to one another in FIG.
  • FIG. 17C at 5 seconds
  • FIG. 17D at 14 seconds
  • FIG. 17E at 20 seconds
  • FIG. 17F at 26 seconds
  • the droplets are merged in FIG. 17G as the diamond pattern pairs align with one another, wherein the droplets mix in FIG. 17H.
  • dipole-dipole interaction between two droplets induces electrocoalescence and combines two droplets together.
  • FIG. 18 illustrates a micro well structure 50 exemplified in a polymer base 52, such as polydimethylsiloxane, generally referred to as PDMS.
  • a polymer base 52 such as polydimethylsiloxane, generally referred to as PDMS.
  • An aqueous droplet 56 is shown being manipulated 58 to a target well 54, which in this example contains a Trypan blue dye (not shown).
  • FIG. 19A-19H depict an image sequence of delivering aqueous droplets to target wells among an array of PDMS wells positioned on an FEOET device. It should be appreciated that although these wells are exemplified as being separate wells, a well as considered herein may comprise any desired structures, microfluidic structures, or droplet interfaces to which one or more droplets can be introduced for a given application.
  • a 1 .28 mm de-ionized water droplet is optically trapped between two diamond- shaped images.
  • FIG. 19C-19H a two-dimensional transport of the droplet is achieved by the corresponding optical image motions which are shown at times of 13, 34, 55, 58 and 60 seconds, respectively.
  • FIG. 19A-19H depict an image sequence of delivering aqueous droplets to target wells among an array of PDMS wells positioned on an FEOET device. It should be appreciated that although these wells are exemplified as being separate wells, a well as considered herein may comprise any desired
  • the droplet is merged into the target well containing Trypan blue.
  • an array of PDMS micro well structures are positioned on top of a FEOET device.
  • these wells are preloaded with aqueous solutions containing the Trypan blue dye and immersed in an oil environment.
  • a 1 .28 mm de-ionized water droplet is transported by a paired diamond-shaped virtual electrode and delivered to the target well to dilute the dye concentration in that well.
  • FIG. 20A-20D illustrate an example of transporting a plurality of droplets, (e.g., sixteen as per this example), in parallel.
  • the droplet size in this demonstration varied from about 0.84 mm to about 1 .3 mm in diameter, although it should be appreciated that a droplet may be of a size from about one micrometer on up to a few millimeters in diameter.
  • the black circles indicate the droplet position in the previous step, while the white circles present the droplet position in the current step.
  • FIG. 20A-20B an array of diamond-shaped optical images are generated to create sixteen traps into whose gaps the droplets are attracted.
  • FIG. 20C-20D parallel transport of the trapped droplets is performed by translation (relative movement) of the dynamic optical images.
  • FIG. 2OC the droplets in the first and third rows are driven to the right side, while the droplets in the second and fourth rows are guided to the left, which continues in FIG. 2OD. Accordingly, the figures demonstrate an ability to transport any desired number of droplets even in opposing directions. [00131] 2.5 Conclusions
  • This section has taught an optically reconfigurable microfluidic platform enabling parallel processing of oil-immersed aqueous droplets on a photoconductive glass substrate using direct optical images.
  • This platform is realized by using optically patterned virtual electrodes, such as paired diamond-shaped patterns, that allow transporting droplets on a two- dimensional FEOET surface.
  • optically patterned virtual electrodes such as paired diamond-shaped patterns
  • This FEOET system is also compatible with other microfluidic structures, such as an array of micro wells.
  • the inventive platform is capable of providing a low cost, droplet-based, microfluidic system for large scale, multiplexed chemical and biochemical screening applications.
  • Droplet-based microfluidic systems have attracted significant interest for their potential utility in high throughput chemical and biological screening. Using a multiphase flow focusing device, tens of thousands of highly uniform, isolated aqueous droplets can be generated in immiscible oil within seconds. Applications, such as fluorescent detection of millisecond chemical kinetics, laser Raman spectroscopic probing, and polymerase chain reactions for high throughput DNA amplification, and others have been demonstrated using droplet-based microfluidic devices.
  • OET optoelectronic tweezers
  • FEOET floating electrode optoelectronic tweezers
  • FIG. 1 An FEOET device was previously described with reference to FIG. 1 whose implementation was exemplified in response to depositing two a-Si:H layers (Q.b ⁇ m undoped and 0.1 ⁇ m n+) on a glass substrate.
  • Two aluminum electrodes separated by a 1 cm gap were deposited at the two edges of the device, for instance by using a lift-off method enabling electrical contact.
  • the n+ a-Si:H layer not covered by Al electrodes was then etched away, for example using a reactive ion etcher.
  • the remaining covered n+ a-S ' wH layer reduces the electrical resistance between the Al electrodes and the undoped a-Si:H layer.
  • PDMS polydimethylsiloxana
  • the perturbed field penetrates into the oil layer, which creates nonuniformity of the electric fields necessary for DEP manipulation in the electrically insulating oil.
  • an electric dipole is also induced on each droplet under the application of a lateral electric field. Even though a highly nonuniform electric field is induced around a droplet, there is no DEP force actuation on the droplet since the balanced electric field distribution around the droplet results in a zero net force.
  • the device is simplified to the following layers: ⁇ ⁇ m a-Si:H, 20 ⁇ m PDMS, and 500 ⁇ m oil medium.
  • a 300 VDC bias is applied at the two end planes along the x direction, and a 300 ⁇ m diameter aqueous droplet is immersed in a 2 X 2 mm oil environment on top of the thin PDMS layer.
  • the dark conductivity of the homogeneous a-Si:H layer is assumed as 10 ⁇ 8 S/m and the optical illumination is assumed to a full width at half maximum to create a Gaussian photoconductivity distribution with its peak conductivity of 10 ⁇ 4 S/m and spot size of 100 ⁇ m .
  • FIG. 21 A-21 C depict 3D numerical simulation results of electric field distribution.
  • FIG. 22A-22C and FIG. 23A-23C illustrate numerical simulations of the electric field distribution around an ionic aqueous droplet loaded into the oil environment.
  • FIG. 22A-22C depicts the e-field without light illumination, wherein the balanced electric field distribution is exhibited around an electric dipole of a droplet. With no light a symmetrical electric field distribution is developed around a droplet, owing to the droplet induced electric dipole, whereby the balanced electric field pattern produces zero net DEP force on the droplet and thus no movement arises.
  • FIG. 23A-23C depicts the e-field in response to optical illumination at the edge of a droplet which creates an unbalanced electric field distribution near the droplet, wherein the DEP force drives a droplet away from the illuminated spot.
  • FIG. 23C The 3D electric field strength distributions on the surface of a droplet are shown in FIG. 22B-22C and FIG. 23B-23C which demonstrate the significant difference in the field patterns with and without light illumination.
  • F [pV)E
  • p the induced dipole
  • E the electric field.
  • a good approximation can be obtained from this equation only when the particle size is much smaller than the gradient of the electric field, criteria that is not satisfied to estimate the DEP force on a droplet whose size is comparable to the light induced electric field gradient.
  • the Maxwell stress tensor is integrated over the whole droplet surface,
  • This estimated DEP force predominates in the x and z directions, meaning that the light-induced virtual electrode raises a droplet and pushes it away from the illuminated spot along the direction of the electric field.
  • the theoretical value of the y direction force should be zero due to symmetry, and the value in the simulation data comes from numerical errors due to limited computation power for 3D simulation.
  • FIG. 24A-24D depict video snapshots of a de-ionized water droplet, immersed in corn oil medium, being repelled by a light beam as predicted by the simulation results of the present invention, and shown at 0s, 3s, 6s and 9s, respectively.
  • Light-induced droplet actuation has been experimentally demonstrated on the FEOET device.
  • a laser beam (3.53 m W at 532 nm ) was utilized with a 1 mm output spot size
  • a charge-coupled device camera e.g., Sony DFW-SX91010 was used with metallic neutral density filters.
  • a maximum droplet speed of 418.6 ⁇ m/s has been achieved on a 748 ⁇ m droplet with a light intensity of 4.49 ⁇ w/ mm 2 .
  • FEOET still allows optical actuation of a 681 ⁇ m droplet at a maximum speed of 85.1 ⁇ m/s .
  • the maximum velocity is limited by the maximum voltage that can be applied to FEOET devices.
  • the electric field strength applied here is 600 V/cm . Applying a higher voltage could provide larger DEP forces and faster droplet motion. It will also be appreciated that aside from bias voltage increases, droplet motion can be sped up by heating the oil, using lower viscosity oils, and so forth.
  • a droplet manipulation mechanism FEOET which enables optical actuation of aqueous droplets in an electrically insulating media on a plain amorphous silicon coated glass device.
  • FEOET allows light patterned virtual electrodes to perturb a uniform electric field distribution, breaking an originally symmetric electric field pattern around a droplet for DEP actuation.
  • the use of FEOET promises a large-scale droplet manipulation platform for parallel droplet processing on a low cost substrate using flexible optical addressing.
  • Microfluidic devices or micro total analysis systems have been developed for providing the prospect to manipulate efficiently the complex protocols in a wide range of applications such as biotechnology, clinical diagnostic, combinatorial chemistry. These systems have the potential to perform various fluidic handling functionalities while offering the advantages of minimal reagent consumption, portability, decreased operating costs, and high throughput.
  • two types of devices are considered, such as a continuous-flow devices and digitized microfluidic devices.
  • a continuous-flow devices In traditional continuous-flow microfluidic devices, multiple streams of liquids are guided within micro channels by regulating their flow rates.
  • Digitized microfluidic systems have found applications in an expanding number of fields, including enzymatic kinetic assays, protein crystallization, and polymerase chain reactions (PCR) for high throughput DNA amplification.
  • PCR polymerase chain reactions
  • Drawbacks of these conventional microfluidic systems include: (1 ) the need of complex mechanical components, such as pumps, valves, tubing and so forth, to guide digitized droplets within micro channels; and (2) the inefficiency in active control of individual droplets interfered by micro channels being driven by a continuous oil flow.
  • Various actuation mechanisms for effective droplet control have been investigated to overcome these drawbacks, such as thermocapillary, dielectrophoresis (DEP), electrowetting on dielectric (EWOD), surface acoustic wave, and magnetic forces.
  • DEP dielectrophoresis
  • EWOD electrowetting on dielectric
  • surface acoustic wave surface acoustic wave
  • OET optoelectronic tweezers
  • an electrically-based droplet driving mechanisms such as EWOD or DEP-based techniques require the electrical activation on 2D digitized metal electrodes
  • the FEOET device of the present invention uses optically-induced electrical field nonuniformity resulting from the modulation of a lateral electric field (one-directional electric field modulation) applied on electrodes on opposing sides, or ends, of the chamber.
  • this lateral electric field modulation using circular laser illumination limits the droplet movement to a linear motion along the direction of electric field, which may restrict potential applicability in chemical and biological applications necessary for multiplexed microfluidic functionalities.
  • an optically reconfigurable droplet-based microfluidic platform enabling an effective 2D addressing of aqueous droplets, which is realized by utilizing one or more pairs of diamond-shaped virtual electrodes.
  • the optical illumination of a pair of these images generates the spatial electric field modulation, resulting in continuous 2D droplet manipulation capability on a FEOET platform.
  • Optically patternable virtual electrodes produce dielectrophoretic (DEP) forces to manipulate aqueous droplets containing chemical and biochemical contents and to perform various microfluidic functions, such as two-dimensional transport, droplet merging and parallel processing of any desired plurality of droplets (e.g., sixteen shown by way of example).
  • DEP dielectrophoretic
  • FIG. 26 illustrates an example embodiment 70 of a flexible and reconfigurable FEOET-based microfluidic platform.
  • the test sample droplets which contain biological cells with physiological buffer solutions, are prepared on a PDMS coated substrate, for example a thin flat surface, an array of micro well structures, other microfluidic structures or combination thereof.
  • a PDMS coated substrate for example a thin flat surface, an array of micro well structures, other microfluidic structures or combination thereof.
  • These sample preparations are very flexible according to biochemical compatibility with a FEOET device.
  • the PDMS substrate with the sample cells is loaded on a photoconductive layer and electrically-insulating oil medium covers it in order to prevent such a small volume of the sample droplets from evaporating in air.
  • Multiple droplets containing different biochemical reagents are introduced and mixing can be performed 72, followed by transport 76 through an array of cells 74 to a target cell (sample) 78.
  • the optically-induced DEP force enables actively driving these droplets for 2D transport in response to light 34 from projector 32.
  • Droplets can be merged or otherwise manipulated during transport to each given target cell.
  • the PDMS substrate is taken out from the device and the cells are inspected for biological analysis. It will be appreciated that the FEOET system in this regard can be configured as a laboratory on a chip.
  • FIG. 27 depicts the layered structure of the FEOET device shown in FIG. 26, which by way of example depict similar layers as in FIG. 1 with a transparent substrate 12, photoconductive layer 14, electrode 18 and PDMS chamber (substrate) containing wells, or other microfluidic receptacles or structures.
  • the fabrication process is relatively simple and featureless when compared to other droplet actuation devices in which the 2D digitized physically deposited metal electrodes are required for electrical activations.
  • the device consists of two layer depositions: a 100 nm a-S ' wH layer and '] 00 nm aluminum electrodes with 5 cm separation at the two edges on a glass substrate.
  • Test sample droplets and cells are loaded into an oil medium retained in an open poly- dimethylsiloxana (PDMS) chamber which is fixed on top of the a-Si:H layer.
  • PDMS poly- dimethylsiloxana
  • the FEOET device described in prior sections was able to actuate an aqueous droplet by light-induced DEP forces with an intensity as low as 4 ⁇ W/mm 2 , an intensity promising the ability to create a large area droplet manipulation platform with commercially available optical projectors or LCD computer monitors, as shown in the lower portion of FIG. 26, without the need of extra optics components.
  • the DEP force induced on the FEOET is definitely dependent upon the direction of applied electric field and shape of optical virtual electrodes.
  • the strong electric field region created between a pair of virtual electrodes induces an optical trap and enables 2D active addressing of a droplet into the position of the two-image gap as shown in FIG. 9C-9D.
  • the device is able to provide a droplet with the same order of magnitude DEP forces in both directions parallel and perpendicular to the applied field.
  • This advancement enables active control of individual droplets and offers the possibility of implementing featureless, low-cost silicon-coated microfluidic platform which are programmable for a flexible and dynamic addressing of optical image patterns in order to perform large scale, multiplexed droplet-based biological and chemical analyses.
  • F dep [-1.07, 0.00, -0.32] x 10 "8 N , corresponding to the force components in x, y, and z directions, respectively.
  • Transporting droplets in the y direction is not as effective as transport in the x direction using a circular light beam. Illuminating a droplet edge at the direction perpendicular (y direction) to the electric field fails to transport the droplet since the electric field strength difference between the illuminated and non-illuminated sides on the droplet surface is too small as shown in FIG. 1 1 A-1 1 B.
  • the y direction force magnitude is 107 times smaller than that of the x direction force in FIG. 10A-
  • FIG. 12 showed the simulation results of a droplet trapped by a paired diamond-shaped image illumination.
  • a droplet is located at the same location as the situation in a circular laser beam illumination, 150 //m away from the center between two diamond-shaped images along the direction parallel (FIG. 13B) and perpendicular (FIG. 14B) to the applied electric field.
  • the photoconductivity profile by two diamond- shaped virtual electrodes is assumed to have the same peak photoconductivity of 10 4 S I m and a 200 ⁇ m separation gap.
  • the electric field strength Prior to loading a droplet, the electric field strength is strongly enhanced at the gap between these two electrodes, as was shown in FIG. 12.
  • This strong electric field region enables the optical trap pattern between the images to attract a droplet.
  • the enhanced electric field can generate DEP forces trapping the droplet into the center of the gap.
  • the value of the DEP force in the x direction is similar to the one in case of a circular laser beam. [00181] For the situation of a droplet positioned 150 ⁇ m away from the gap center along the y direction, however, the DEP force shows a dramatic increase compared to the y direction force in the case of a circular light beam.
  • the y direction force is only 2.41 times smaller than the x direction force in the FIG. 13B situation. This value shows a dramatic improvement compared to the 107 times smaller in the circular light beam case.
  • This y direction force is able to provide effective trapping and transporting of a droplet in the y direction, and also realizes effective 2D droplet manipulation functions on FEOET devices.
  • the power consumption of the whole device is a couple of hundred ⁇ W in the dark state and less than a few m W in the bright state due to the large electrical impedance of the oil and a-Si:H thin film ( - 1014 ⁇ in the dark state) in the lateral direction.
  • FIG. 16A-16E Video snapshots of 2D transport of a 1 .47 mm aqueous droplet containing the Trypan blue dye were shown in FIG. 16A-16E. Initially the droplet is located at 4.5 mm away from the center of two projected diamond- shaped virtual electrodes as shown in FIG. 16A. These images indicate the strong electric field region produced in the center of the images which cause the optically-induced droplet trap in response to applied bias voltage. Then the droplet is attracted to such an optically-induced trap and the continuous 2D transport of the droplet in both x and y directions is now achieved by following the motion of paired diamond-shaped images as shown in FIG. 16C through
  • FIG. 16E The droplet transport speed is 721 ⁇ m/s in the x direction and
  • FIG. 28A-28F illustrates images from a demonstration similar to the above, however, in this case the pattern images were generated by an LCD computer monitor upon which the FEOET device was positioned. After gently positioning the FEOET device on the LCD monitor, images are directly patterned to the device without any additional optical components. Because of the pixilated LCD images, their intensity and contrast are greatly lower than the one from the projector illumination. Nevertheless, continuous 2D transport of a 1 .54 mm de-ionized (Dl) water droplet was achieved by LCD image motions of 5 ⁇ 5 ⁇ mfs in the x direction and 221 ⁇ m/s in the y direction. [00187] In this sequence, FIG. 28A depicts the initial position of the droplet before trapping.
  • Dl de-ionized
  • FIG. 28D at time equal to 38 seconds, the droplet has been moved upward in response to the diamond pattern, then in FIG. 28E the droplet was moved back to the right, and in FIG. 28F the droplet was moved back down to its original position.
  • FIG. 18 illustrated a simple example of a 2 x 3 array of PDMS-fabricated micro well structures. It should be appreciated that these wells can contain any desired molecular or biological specie, for example adherent cells pre-grown in these micro wells with physiological buffer solutions and loaded into the FEOET device according to the present invention.
  • FIG. 29A-29E demonstrates operation of the FEOET wherein Trypan blue dye droplets are confined in the micro wells, with the PDMS structure positioned on top of a FEOET device, being immersed in an oil environment.
  • FIG. 29A depicts the initial position of the droplet with the bias voltage off.
  • FIG. 29B the bias voltage is turned on, and the droplet is seen trapped by the electrodes in FIG. 29C, shown at 45 seconds, then in FIG. 29D the droplet is depicted immediately prior to merging into the target well at 60 seconds, and finally in FIG. 29E the droplet is shown upon delivery to the well.
  • FIG. 17A-17H depicts an example of two 1 mm droplets containing red and green food coloring dyes being individually manipulated and merged together.
  • dipole-dipole interaction between two droplets induces electrocoalescence and combines two droplets together.
  • FIG. 30A-30E depicts a sequence of images showing that mixing inside the droplet is achieved by a simple movement of the droplet. The friction with the solid surface induces the shear flow inside the droplet for mixing while optical transport is taking place within the FEOET.
  • FIG. 3OA shows the two droplets prior to merging and coalescing, then in FIG. 3OB after droplet merging.
  • a DEP force drives the merged droplet and as seen in FIG. 3OD at a time of 4s, wherein the shearing flow inside the droplet causes mixing within the droplet which is substantially intermixed by FIG. 3OE shown at a time of 8 seconds.
  • FIG. 31 A-31 D illustrate a successful demonstration of the enhancement of fluorescent signal for HeLa cell detection using a FEOET device. This process is accomplished by optical manipulation of the droplet of trimethyltin (TMT) chloride for activation of intracellular calcium [ CaJ + ) with HeLa cells.
  • TMT trimethyltin
  • FIG. 31 A The intensity increase of fluo-4 preloaded HeLa cells corresponds with the level of CaJ + flux into cells as depicted in FIG. 31 B.
  • the cells are shown with both fluo-4 and TMT in FIG. 31 C. No photobleaching was observed for up to a few hours.
  • FIG. 31 D HeLa cells are shown loaded with fluo-4, CaJ + , and TMT in which a greatly enhanced fluorescent signal can be seen. This greatly enhanced signal arises because the application of TMT elevates CaJ + flux, resulting in reactions with fluo-4.
  • HeLa cells in this example were maintained at 37°C and 5% CO2 in
  • DMEM fetal calf serum
  • FIG. 32A-32E demonstrates TMT droplet transport into Fluo-4 loaded cells in DMEM/CaCI 2 .
  • FIG. 32A depicts TMT loading, wherein a TMT droplet is seen, as well as a Fluo-4 preloaded HeLa cell and a target cell.
  • FIG. 33A-33B demonstrate the positive result of droplet manipulation as clearly indicated by the noticeable fluorescent intensity elevation observed between TMT activated (FIG. 33A) and non-activated droplets (FIG. 33B).
  • FIG. 33A-33B demonstrate the positive result of droplet manipulation as clearly indicated by the noticeable fluorescent intensity elevation observed between TMT activated (FIG. 33A) and non-activated droplets (FIG. 33B).
  • FIG. 33A-33B demonstrate the positive result of droplet manipulation as clearly indicated by the noticeable fluorescent intensity elevation observed between TMT activated (FIG. 33A) and non-activated droplets (FIG. 33B).
  • FIG. 33A-33B demonstrate the positive result of droplet manipulation as clearly indicated by the noticeable fluorescent intensity elevation observed between TMT activated (FIG. 33A) and non-activated droplets (FIG. 33B).
  • FIG. 33A-33B demonstrate the positive result of droplet manipulation as clearly indicated by the noticeable fluorescent intensity elevation observed between TMT activated (FIG. 33A) and non-activated
  • FEOET platform several important droplet manipulation functions have been demonstrated, including: continuous 2D droplet transport, droplet merging and parallel processing of any desired plurality of droplets.
  • the FEOET system of the present invention is also compatible with other microfluidic structures, such as micro wells arrays.
  • This inventive platform promises a low cost, droplet- based, microfluidic system for large scale, multiplexed chemical and biochemical screening applications.

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Abstract

L'invention concerne un dispositif de pinces optoélectroniques à électrodes flottantes (FEOET) pour la manipulation optique de gouttelettes immergées dans l'huile sur une couche photoconductrice sans éléments en réponse au déplacement d'images optiques, et mieux encore, de paires d'images optiques retenues à proximité suffisante pour le piégeage de gouttelettes. Dans un mode de réalisation, des électrodes sont liées à une couche photoconductrice conçue avec une chambre destinée à retenir un milieu liquide et des gouttelettes aqueuses. Une polarisation de tension suffisante est appliquée sur les électrodes et un motif de lumière 2D est dirigé sur la couche photoconductrice afin de former des électrodes virtuelles qui dirigent des déplacements de gouttelettes aqueuses par diélectrophorèse (DEP). Les gouttelettes aqueuses contiennent des constituants chimiques et biochimiques qui peuvent être manipulées, à savoir piégées, transportées en 2D, fusionnées, coalescées, acheminés vers des puits ou d'autres structures. Ledit système microfluidique basé sur des gouttelettes présente une large applicabilité, tel que dans le criblage chimique et biologique à haut rendement.
PCT/US2008/078476 2007-10-02 2008-10-01 Plateforme de pinces optoélectroniques à électrodes flottantes (feoet) pour manipulation optique de gouttelettes immergées dans l'huile Ceased WO2009046125A2 (fr)

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WO2013181288A1 (fr) * 2012-05-30 2013-12-05 Berkeley Lights, Inc. Sortie d'une gouttelette de milieu liquide d'un dispositif pour traitement de micro-objets dans le milieu
CN105486867A (zh) * 2014-09-19 2016-04-13 中国科学院沈阳自动化研究所 基于光诱导介电泳机械力的免标记细胞电特性获取方法
US9533306B2 (en) 2010-08-02 2017-01-03 The Regents Of The University Of California Single sided continuous optoelectrowetting (SCEOW) device for droplet manipulation with light patterns
US9815056B2 (en) 2014-12-05 2017-11-14 The Regents Of The University Of California Single sided light-actuated microfluidic device with integrated mesh ground
US10675625B2 (en) 2016-04-15 2020-06-09 Berkeley Lights, Inc Light sequencing and patterns for dielectrophoretic transport
US10799865B2 (en) 2015-10-27 2020-10-13 Berkeley Lights, Inc. Microfluidic apparatus having an optimized electrowetting surface and related systems and methods
US11007520B2 (en) 2016-05-26 2021-05-18 Berkeley Lights, Inc. Covalently modified surfaces, kits, and methods of preparation and use
US11365381B2 (en) 2015-04-22 2022-06-21 Berkeley Lights, Inc. Microfluidic cell culture
WO2023281274A1 (fr) * 2021-07-09 2023-01-12 Lightcast Discovery Ltd Perfectionnements apportés ou se rapportant à l'imagerie de microgouttelettes dans un dispositif microfluidique

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US6734436B2 (en) * 2001-08-07 2004-05-11 Sri International Optical microfluidic devices and methods
WO2005100541A2 (fr) * 2004-04-12 2005-10-27 The Regents Of The University Of California Pinces optoelectroniques pour la manipulation de microparticules et de cellules

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US9533306B2 (en) 2010-08-02 2017-01-03 The Regents Of The University Of California Single sided continuous optoelectrowetting (SCEOW) device for droplet manipulation with light patterns
WO2013181288A1 (fr) * 2012-05-30 2013-12-05 Berkeley Lights, Inc. Sortie d'une gouttelette de milieu liquide d'un dispositif pour traitement de micro-objets dans le milieu
CN105486867A (zh) * 2014-09-19 2016-04-13 中国科学院沈阳自动化研究所 基于光诱导介电泳机械力的免标记细胞电特性获取方法
US9815056B2 (en) 2014-12-05 2017-11-14 The Regents Of The University Of California Single sided light-actuated microfluidic device with integrated mesh ground
US10569271B2 (en) 2014-12-05 2020-02-25 The Regents Of The University Of California Single-sided light-actuated microfluidic device with integrated mesh ground
US11365381B2 (en) 2015-04-22 2022-06-21 Berkeley Lights, Inc. Microfluidic cell culture
US12134758B2 (en) 2015-04-22 2024-11-05 Bruker Cellular Analysis, Inc. Microfluidic cell culture
US10799865B2 (en) 2015-10-27 2020-10-13 Berkeley Lights, Inc. Microfluidic apparatus having an optimized electrowetting surface and related systems and methods
US11964275B2 (en) 2015-10-27 2024-04-23 Berkeley Lights, Inc. Microfluidic apparatus having an optimized electrowetting surface and related systems and methods
US11376591B2 (en) 2016-04-15 2022-07-05 Berkeley Lights, Inc. Light sequencing and patterns for dielectrophoretic transport
US10675625B2 (en) 2016-04-15 2020-06-09 Berkeley Lights, Inc Light sequencing and patterns for dielectrophoretic transport
US11007520B2 (en) 2016-05-26 2021-05-18 Berkeley Lights, Inc. Covalently modified surfaces, kits, and methods of preparation and use
US11801508B2 (en) 2016-05-26 2023-10-31 Berkeley Lights, Inc. Covalently modified surfaces, kits, and methods of preparation and use
US12280370B2 (en) 2016-05-26 2025-04-22 Bruker Cellular Analysis, Inc. Covalently modified surfaces, kits, and methods of preparation and use
WO2023281274A1 (fr) * 2021-07-09 2023-01-12 Lightcast Discovery Ltd Perfectionnements apportés ou se rapportant à l'imagerie de microgouttelettes dans un dispositif microfluidique

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