WO2021074635A1 - Appareil et procédés de manipulation de microgouttelettes par application d'une force d'électrodémouillage - Google Patents

Appareil et procédés de manipulation de microgouttelettes par application d'une force d'électrodémouillage Download PDF

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Publication number
WO2021074635A1
WO2021074635A1 PCT/GB2020/052606 GB2020052606W WO2021074635A1 WO 2021074635 A1 WO2021074635 A1 WO 2021074635A1 GB 2020052606 W GB2020052606 W GB 2020052606W WO 2021074635 A1 WO2021074635 A1 WO 2021074635A1
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layer
microdroplets
photoactive layer
surfactant
carrier fluid
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PCT/GB2020/052606
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English (en)
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Thomas Henry ISAAC
Rebecca Natalie PALMER
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Lightcast Discovery Ltd
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Publication of WO2021074635A1 publication Critical patent/WO2021074635A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
    • B01L3/50—Containers for the purpose of retaining a material to be analysed, e.g. test tubes
    • B01L3/502—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures
    • B01L3/5027—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip
    • B01L3/502769—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip characterised by multiphase flow arrangements
    • B01L3/502784—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip characterised by multiphase flow arrangements specially adapted for droplet or plug flow, e.g. digital microfluidics
    • B01L3/502792—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip characterised by multiphase flow arrangements specially adapted for droplet or plug flow, e.g. digital microfluidics for moving individual droplets on a plate, e.g. by locally altering surface tension
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/16—Surface properties and coatings
    • B01L2300/161—Control and use of surface tension forces, e.g. hydrophobic, hydrophilic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/16—Surface properties and coatings
    • B01L2300/161—Control and use of surface tension forces, e.g. hydrophobic, hydrophilic
    • B01L2300/163—Biocompatibility
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2300/00—Additional constructional details
    • B01L2300/16—Surface properties and coatings
    • B01L2300/168—Specific optical properties, e.g. reflective coatings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L2400/00—Moving or stopping fluids
    • B01L2400/04—Moving fluids with specific forces or mechanical means
    • B01L2400/0403—Moving fluids with specific forces or mechanical means specific forces
    • B01L2400/0415—Moving fluids with specific forces or mechanical means specific forces electrical forces, e.g. electrokinetic
    • B01L2400/0427—Electrowetting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
    • B01L3/50—Containers for the purpose of retaining a material to be analysed, e.g. test tubes
    • B01L3/502—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures
    • B01L3/5027—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip
    • B01L3/502707—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures by integrated microfluidic structures, i.e. dimensions of channels and chambers are such that surface tension forces are important, e.g. lab-on-a-chip characterised by the manufacture of the container or its components

Definitions

  • the present disclosure relates to a device and associated methods for manipulating microdroplets, and in particular to a microfluidic chip configured to manipulate microdroplets by application of electro-dewetting force.
  • the technical field generally relates to methods and devices used to manipulate fluids and more specifically to methods and devices that utilize the effect of an applied electrical field that makes a liquid less wetting on a surface than the natural state.
  • Electrowetting is a well-known effect in which an electric field applied between a liquid and a substrate makes the liquid more wetting on the surface than the natural state.
  • the effect of electrowetting can be used to manipulate (e.g., move, divide, change shape) fluids by applying a series of spatially configured electrical fields on a substrate to increase the surface wettability following the spatial configurations in a sequence.
  • Devices for manipulating droplets or magnetic beads by application of electro-wetting force have been previously described in the art; see for example US6565727, US20130233425 and US20150027889.
  • Such devices, which employ what hereinafter will be referred to as ‘real’ electrowetting electrodes are known in the art by the acronym EWOD (Electrowetting on Dielectric) devices. Since most reliable dielectric materials are hydrophilic but electrowetting is most effective on a hydrophobic surface, most EWOD devices require a hydrophobic topcoat that is interposed between the surface of a substrate and the fluid.
  • OEWOD optically mediated electrowetting
  • the microdroplets are translocated through a microfluidic space defined by containing walls; for example a pair of parallel plates having the microfluidic space sandwiched therebetween.
  • At least one of the containing walls includes what are hereinafter referred to as ‘virtual’ electrowetting electrodes locations which are generated by selectively illuminating an area of a semiconductor layer buried within.
  • WO2018/234445 an improved version of the OEWOD approach is described which enables many thousands of microdroplets, in the size range less than 10pm, to be manipulated simultaneously and at velocities higher than have been observed hereto.
  • Another advantage associated with the device of WO2018/234445 is that conductive cells are dispensed with and hence permanent droplet-receiving locations are abandoned in favour of a homogeneous dielectric surface on which the droplet- receiving locations are generated ephemerally by selective and varying illumination of points on the photoconductive layer using for example a pixellated light source.
  • the device of WO2018/234445 comprises a second optional layer of high-strength dielectric material on the second composite wall, and a very thin anti-fouling layer which negates the inevitable reduction in electrowetting field caused by overlaying a low-dielectric-constant anti-fouling layer.
  • a typical EWOD device includes a substrate with electrodes patterned on it and a dielectric layer covering the electrodes.
  • the dielectric layer is covered with a thin layer of hydrophobic topcoat, so that water (or another fluid) beads on the topcoat surface in its natural (i.e., hydrophobic) state and wets the surface when an electric field is applied between the fluid and the electrode.
  • hydrophobic topcoat leads to several important difficulties and disadvantages. First, most materials, whether natural or engineered, are hydrophilic.
  • Polymers tend to have a relatively low surface energy and are relatively less wettable, but only a small number of them, such as PTFE (Teflon®, Cytop®, etc.), are hydrophobic enough to make high-performance EWOD devices.
  • PTFE Teflon®, Cytop®, etc.
  • the strong hydrophobic materials come with a low surface energy, making it difficult to coat them on to another material.
  • the most typical failure mechanism for both EWOD devices and OEWOD devices is through dielectric breakdown, in which one or more of the insulating layers degrades upon application of the bias voltage.
  • the surfaces such as collagen, laminin and UV-activated polystyrene which are commonly used to promote cell adhesion are generally hydrophilic.
  • WO201 7/127505 and Nature 572, 507-510 (2019) describe methods wherein droplet manipulation is achieved using electrical signals to induce the liquid to dewet the surfaces of the fluidic device, rather than wet.
  • the liquid- substrate interaction is not controlled directly by electric field but instead by field- induced dispersal of ionic surfactants away from the interface between the substrate and the droplet and the interface between the droplet and the continuous phase fluid; in the case of the given references the continuous phase fluid is generally air and for a de-wetting effect the ionic surfactants are dispersed away from the three-way droplet/air/substrate interface.
  • the continuous phase fluid is generally air and for a de-wetting effect the ionic surfactants are dispersed away from the three-way droplet/air/substrate interface.
  • permanent physically-patterned electrodewetting electrodes are employed.
  • the present invention provides an apparatus and associated methods for manipulating microdroplets by application of an electrodewetting force that is optically-mediated (optoelectrodewetting).
  • the electrodewetting effect can achieve what much of the well-accepted electrowetting effect (especially EWOD) does but without facing the main limitations of the latter.
  • the main advantage of electrodewetting-based microfluidics over the electrowetting-based microfluidics is its ability to use hydrophilic surfaces in contact with liquids.
  • the use of a hydrophilic surface is a major advantage, considering most of the main shortcomings of the EWOD-based microfluidics stem from its necessary use of a hydrophobic topcoat. Without any topcoat, electrodewetting-based microfluidic devices are simpler to manufacture than EWOD devices and are free of the above listed problems.
  • An electrodewetting device can have a Si02 surface for example.
  • the operating voltages required for electrodewetting are substantially lower than those required for EWOD. Running such devices at lower voltages means they can run at potentials that are too low to cause electrolysis, electrophoresis or cell lysis. Furthermore, it is necessary to carefully control the amount of current drawn through the droplet in electrodewetting devices; accumulation or dispersal of the ionic surfactant must be carefully modulated so as not to cause bubbling through electrolysis whilst still driving sufficient surfactant away from the interface and ensuring the proportion of the surfactant dispersed is appropriate given the initial surfactant concentration. As such precise control over the driving current applied to the surfactant, particularly around the droplet/continuous phase/substrate interfacial meeting point, is highly advantageous in an optoelectrodewetting device.
  • the presently disclosed apparatus makes use of a photoconductor layer which allows continuous variation of the resistivity of the terminal layer of the device and hence precise control of the amount of current driven proximally to the droplet/continuous phase/substrate interface.
  • resistivity of the leaky dielectric layer is fixed at the point of fabrication. It is well known the that resistivity of such dielectric layers is generally inhomogenous and uncontrolled on the microscopic scale; elements such as pinhole defects and thickness inhomogeneities impact the resistivity of the layer.
  • the device of the present invention does not require dielectric insulator layers or layers comprising materials that render the inner surfaces of the device hydrophobic as is required in devices known in the art that are based on electrowetting, and it does not require ‘leaky’ dielectric layers as is required in devices known in the art to drive electrodewetting.
  • the microfluidic substrates of the apparatus have no patterned electrodes, removing several complex low-yield fabrication steps and simplifying the electrical interconnections in comparison to conventional approaches. Device failures caused by dielectric breakdown between neighbouring electrodes are eliminated thereby.
  • a simplified electrodewetting photoactive stack is thus described which requires a surprisingly thin photoactive layer.
  • the disclosed apparatus advantageously allows for the manipulation of microdroplets with a high level of control across a wide range of sizes, and being digitally controlled, provides for dynamically re-programmable operational steps.
  • the resulting device structure permits more elaborate and integrated workflows compared to conventional approaches, such as independent control of the carrier phase and the droplets, as well as allowing for a greater density of droplets to be controlled across regions of the microfluidic chip surface.
  • a device for manipulating microdroplets using optically-mediated electrodewetting comprising: a first composite wall comprised of: a first substrate; a first conductor layer on the first substrate; and a photoactive layer on the first conductor layer, the photoactive layer having a hydrophilic surface and a thickness of less than 150nm; a second composite wall comprised of: a second substrate; a second conductor layer on the second substrate; wherein the hydrophilic surface of the photoactive layer and the exposed surface of the second conductor layer define a microfluidic space configured to hold microdroplets in an immiscible carrier fluid, one of the immiscible carrier fluid and the microdroplets containing a surfactant; a power source configured to provide a voltage across the first and second composite walls; and a source of electromagnetic radiation configured to impinge on the photoactive layer to create one or more de-wetting locations on the photoactive layer, such that the contact angle of one or more droplets located on or adjacent to the
  • the first and second walls of the device can form or are integral with the walls of a transparent chip or cartridge with the microfluidic space sandwiched between.
  • the first substrate and first conductor layer are transparent enabling light from the source of electromagnetic radiation (for example multiple laser beams or LED diodes) to impinge on the photoactive layer.
  • all layers are transparent.
  • the first and second substrates are made of a material which is mechanically strong for example glass, metal, crystalline semiconductor wafer or an engineering plastic. In one embodiment, the substrates may have a degree of flexibility.
  • the first and second conductor layers are located on one surface of the first and second substrates.
  • at least one of these layers is made of a transparent conductive material such as Indium Tin Oxide (ITO), a very thin film of conductive metal such as silver or a conducting polymer such as PEDOT or the like.
  • ITO Indium Tin Oxide
  • PEDOT conducting polymer
  • These layers may be formed as a continuous sheet or a series of discrete structures such as wires.
  • the conductor layer may be a mesh of conductive material with the electromagnetic radiation being directed between the interstices of the mesh.
  • the first conductor layer may be transparent.
  • the second conductor layer may be transparent.
  • the exposed internal surfaces of the device are suitably hydrophilic.
  • the exposed second conductor layer is suitably hydrophilic.
  • the exposed a photoactive layer on the first conductor layer is suitably hydrophilic.
  • the photoactive layer is suitably comprised of a semiconductor material which can generate localised areas of charge carriers in response to illumination with a source of electromagnetic radiation.
  • a semiconductor material which can generate localised areas of charge carriers in response to illumination with a source of electromagnetic radiation.
  • Examples include fully hydrogenated amorphous silicon layers.
  • Examples include a substantially uniform layer of fully hydrogenated amorphous silicon.
  • the photoactive layer is activated by the use of visible light.
  • the photoactive layer possesses a hydrophilic surface.
  • the photoactive layer possesses a thickness of less than 150nm.
  • the photoactive layer may possess a thickness of 100nm or less.
  • these photoactive structures and opposing conductive layers are coated with an anti-fouling layer to assist in the establishing the desired microdroplet/carrier fluid/surface contact angle at the various virtual electrodewetting locations, and additionally to prevent the contents of the microdroplets adhering to the surface and being diminished as the microdroplet is moved through the chip.
  • the anti-fouling layer may be partially conducting or conducting.
  • One or more of the surfaces defining the microfluidic space may be coated with a conductive anti-fouling layer.
  • the second anti-fouling layer may be applied directly onto the second conductor layer.
  • the anti-fouling layer should assist in establishing a microdroplet/carrier fluid/surface contact angle that should be below 90° when measured at an air-liquid-surface three-point interface at 25°C.
  • these layer(s) have a thickness of less than 10nm and may be a monomolecular layer.
  • the anti-fouling layer or layers comprise a layer of covalently coupled PEG-silane. Either or both of the anti-fouling layers are hydrophilic to ensure optimum performance.
  • the photoactive layer and the second conductor layer and therefore the first and second walls define a microfluidic space in which the microdroplets are contained.
  • the microdroplets Before they are contained in this microdroplet space, the microdroplets may themselves have an intrinsic diameter which may be more than 10% greater, or more than 20% greater, than the width of the microdroplet space. This may be achieved, for example, by providing the device with an upstream inlet, such as a microfluidic orifice, where microdroplets having the desired diameter are generated in the carrier medium.
  • an upstream inlet such as a microfluidic orifice
  • the microfluidic space includes one or more spacers for holding the first and second walls apart by a predetermined amount.
  • Options for spacers include beads or pillars, ridges created from an intermediate resist layer which has been produced by photo-patterning.
  • Various spacer geometries can be used to form narrow channels, tapered channels or partially enclosed channels which are defined by lines of pillars. By careful design, it is possible to use these structures to aid in the deformation of the microdroplets, subsequently perform droplet splitting and effect operations on the deformed droplets.
  • the first and second walls are biased using a source of D/C power attached to the conductor layers to provide a voltage potential difference therebetween.
  • the voltage potential difference may be in the range of 5 to 50V.
  • the structures described herein are typically employed in association with a source of second electromagnetic radiation having a wavelength in the range 400-850nm, preferably 660nm, and an energy higher than the bandgap of the photoactive layer.
  • the photoactive layer will be activated at the virtual electrodewetting locations.
  • the source of electromagnetic radiation is, in one embodiment, pixelated so as to produce corresponding photoexcited regions on the photoactive layer which are also pixelated. By this means, pixelated virtual electrodewetting locations are induced on the photoactive layer.
  • the source of electromagnetic radiation is pixelated it may be supplied either directly or indirectly using a reflective screen such as a digital micromirror device (DMD) illuminated by light from LEDs or other lamps.
  • DMD digital micromirror device
  • This enables highly complex patterns of virtual electrodewetting locations to be rapidly created and destroyed on the photoactive layer thereby enabling the microdroplets to be precisely steered along essentially any virtual pathway using closely-controlled electrodewetting forces. This is also especially advantageous where there is a requirement for the chip to manipulate many thousands of such microdroplets simultaneously along multiple pathways.
  • Such electrodewetting pathways can be viewed as being constructed from a continuum of virtual electrodewetting locations on the photoactive layer. Absent any illumination, all points on the surface of first conductor layer have an equal propensity to become electrodewetting locations. Overall this makes the device very flexible and the electrodewetting pathways highly programmable.
  • the points of impingement of the sources of electromagnetic radiation on the photoactive layer can be any convenient shape.
  • the morphologies of these points are determined by the morphologies of the corresponding pixelations and in another correspond wholly or partially to the morphologies of the microdroplets once they have entered the microfluidic space.
  • the points of impingement and hence the electrodewetting locations may be crescent-shaped and orientated in the intended direction of travel of the microdroplet.
  • the electrodewetting locations themselves are smaller than the microdroplet surface adhering to the first wall and give a maximal field intensity gradient across the contact line formed between the droplet and the photoactive layer.
  • the device of the present invention may comprise means for manipulating the points of impingement of the electromagnetic radiation on the photoactive layer so as to vary the arrangement of the dewetting locations, thereby creating at least one pathway along which the microdroplets are manipulated.
  • the means for manipulating the points of impingement of the electromagnetic radiation on the photoactive layer is adapted or programmed to produce a plurality of concomitantly-running, for example parallel, first electrodewetting pathways on the photoactive layer.
  • it is adapted or programmed to further produce a plurality of second electrodewetting pathways on the photoactive layer which intercept with the first electrodewetting pathways to create at least one microdroplet-coalescing location where different microdroplets travelling along different pathways can be caused to coalesce.
  • the first and second electrodewetting pathway may intersect at right-angles to each other or at any angle thereto including head-on.
  • microdroplets are dispersed in the form of an emulsion.
  • the emulsion may be a water-in-oil emulsion.
  • the emulsion employed is an emulsion of aqueous microdroplets in an immiscible carrier solvent medium comprised of a hydrocarbon, fluorocarbon or silicone oil.
  • the emulsion suitably comprises surfactants which may be contained in the aqueous microdroplets, in the immiscible carrier fluid or may be present at or near the microdroplet-carrier fluid interface.
  • the surfactants may be chosen so as ensure that the microdroplet/carrier medium/electrodewetting surface location contact angle is optimal.
  • the surfactant may be a cationic surfactant.
  • the surfactant may be an anionic surfactant.
  • the surfactant may comprise one or more of dodecyl trimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and tetradecylmethylammonium bromide (TTAB).
  • the surfactant may comprise one or more of sodium dodecyl sulfate (SDS), 1-hexadecanesulfonic acid sodium salt (HDSAS), sodium tetradecyl sulfate (STS), and sodium decyl sulfate (SI OS).
  • the device may be in the form of a microfluidic chip.
  • a device for manipulating microdroplets, the device comprising a microfluidic chip adapted to receive and manipulate microdroplets dispersed in carrier fluid flowing along pathways on a surface of the chip, wherein the microdroplets are manipulated using an optically-mediated electrodewetting force.
  • the device and methods of the present invention may further include a means to analyse the contents of the microdroplets disposed either within the device itself or at a point downstream thereof.
  • this analysis means may comprise a second source of electromagnetic radiation arranged to impinge on the microdroplets and a photodetector for detecting fluorescence emitted by chemical components contained within.
  • the device may include an upstream zone in which a medium comprised of an emulsion of aqueous microdroplets in an immiscible carrier fluid is generated and thereafter introduced into the microfluidic space on the upstream side of the device.
  • the device may comprise a flat chip having a body formed from composite sheets corresponding to the first and second walls which define the microfluidic space therebetween and at least one inlet and outlet.
  • the device of the invention may further comprise an internal coating structure to allow controlled attachment and detachment of adherent cells contained within the microdroplets.
  • the coating structure may be formed on the surface of the chip to facilitate cell adhesion.
  • the coating structure may comprise silicon dioxide.
  • the coating structure may comprise polystyrene.
  • the coating structure may for example comprise a layer of Bovine Serum Albumin (BSA) coupled to the surface via a chemical linker.
  • BSA Bovine Serum Albumin
  • an apparatus for adherent cell culture in which adherent (mammalian) cells are cultured from an emulsion of aqueous microdroplets in oil, and wherein the actuation mechanism for manipulating the cell-containing microdroplets on the surface of a microfluidic chip, and controlling attachment to and detachment from that surface, is optically mediated electrodewetting.
  • adherent mammalian cells
  • the actuation mechanism for manipulating the cell-containing microdroplets on the surface of a microfluidic chip, and controlling attachment to and detachment from that surface is optically mediated electrodewetting.
  • Such a coating structure may be formulated such that it is electrically conducting or partially electrically conducting.
  • the present invention thus may also provide an integrated platform where automated on-chip operations for screening, sorting, and repeated culturing cycles cells can be performed in the same environment.
  • conventional methods require manual handling of cells and repeated transfer of cells to different environments for performing different operations.
  • the device of the present invention may also provide for implementing environment controls suitable for the adherent cell conditions such as: controlled temperature, regions of different flow, controlling the carrier fluid to continuously feed cultured cells a supply of nutrients, and control of the local gas concentration in the carrier fluid surrounding the cultured cells.
  • Conventional plate-based methods also often have high percentage of “empty” wells during analysis.
  • the on-chip sorting and discarding operations enabled by the microfluidic chip of the present invention provide greater efficiency for performing assays.
  • the present invention also provides a device and related methods for the rapid identification, manipulation and selection of cells.
  • Fluid manipulation includes not only sliding or displacement of the droplet along the device but also dividing and shape changing of the droplet.
  • the detection system may be provided to detect one or more microdroplets.
  • One or more microdroplets may utilize light or optical spectroscopy such as fluorescence spectroscopy.
  • a detector can be configured to detect the fluorescence of one or more microdroplets.
  • the detector can be a fluorescence detector. Accordingly, in another aspect of the invention there is also provided a method of manipulating one or more microdroplets in an immiscible carrier fluid using a microfluidic device according to a previous aspect of the invention, one of the microdroplets and the immiscible carrier fluid containing a surfactant, the method comprising: a.
  • microfluidic space receiving one or more microdroplets on a surface of a photoactive layer defining a microfluidic space, the microfluidic space being located between first and second conductor layers of the microfluidic device; b. applying a voltage across the first and second conductor layers; c. causing electromagnetic radiation to impinge on the photoactive layer to reduce the resistivity of the photoactive layer at the point of impingement and create a de-wetting location, thereby inducing an increase in contact angle of one or more microdroplets located on or adjacent to the de-wetting location.
  • the microfluidic device used to carry out the method of manipulating one or more microdroplets in an immiscible carrier fluid may comprise the following features: a first composite wall comprised of: a first substrate; a first conductor layer on the first substrate; and a photoactive layer on the first conductor layer, the photoactive layer having a hydrophilic surface and a thickness of less than 150nm; a second composite wall comprised of: a second substrate; a second conductor layer on the second substrate; wherein the hydrophilic surface of the photoactive layer and the exposed surface of the second conductor layer define a microfluidic space configured to hold microdroplets in an immiscible carrier fluid, one of the immiscible carrier fluid and the microdroplets containing a surfactant; a power source configured to provide a voltage across the first and second composite walls; and a source of electromagnetic radiation configured to impinge on the photoactive layer to create one or more de-wetting locations on the photoactive layer, such that the contact angle of one or more
  • Devices of the type specified above may be used to manipulate adherent cells contained in microdroplets on a surface of the microfluidic chip of the present invention. Accordingly, there is also provided a method of manipulating one or more adherent cells contained in microdroplets on a surface of a microfluidic device of the 10 present invention.
  • FIG. 1 shows a cross-sectional view of a device according to the present invention.
  • FIGs. 2 to 4 show a proof-of-concept 2D simulation of optoelectrodewetting applied to a rectangular droplet using a device of the present invention.
  • FIG. 1 A cross-sectional view of a device according to the invention suitable for the fast manipulation of aqueous microdroplets 1 (aqueous droplet shaded) emulsified into an immiscible carrier fluid is provided in FIG. 1 1.
  • the device comprises top and bottom glass plates 2a and 2b coated with transparent layers of conductive Indium Tin Oxide (ITO) 3a and 3b. Each ITO layer is connected to a D/C source with the BO lower ITO layer 3b being the ground.
  • the lower ITO layer 3b is coated with a layer of amorphous silicon 5.
  • ITO Indium Tin Oxide
  • An image of a reflective pixelated screen, illuminated by an LED light source 4 is disposed generally beneath the lower glass plate 2b and visible light is emitted from each diode and caused to impinge on the layer of amorphous silicon 5.
  • photoexcited regions of charge are created which induce modified liquid-solid contact angles in at corresponding electrodewetting locations. These modified properties provide the capillary force necessary to propel the microdroplets from one point to another.
  • the device is controlled by a microprocessor which determines which diodes in the array are illuminated at any given time by pre-programmed algorithms.
  • surfactant molecules are attracted towards the photoexcited portion of amorphous silicon layer 5, modifying the local contact angles between the droplet and the conductor layers.
  • the device comprises top 2a and bottom 2b glass plates each 500pm thick coated with transparent layers of conductive Indium Tin Oxide (ITO) 3a and 3b having a thickness of 130nm.
  • ITO Indium Tin Oxide
  • Each of the layers of conductive Indium Tin Oxide (ITO) 3 is connected to a D/C source with the ITO layer on bottom glass plate 2b being the ground.
  • the source of D/C power attached to the conductor layers provides a voltage potential difference of 20V.
  • Bottom glass plate 2b is coated with a layer of amorphous silicon 5 which is 100nm thick.
  • Top glass plate 2a and the layer of amorphous silicon 5 are spaced 8pm apart using spacers (not shown) so that the microdroplets undergo a degree of compression when introduced into the device cavity.
  • An image of a reflective pixelated screen, illuminated by an LED light source 4 is disposed generally beneath bottom glass plate 2b and visible light (wavelength 660 or 830nm) at a level of O.OIWcm 2 is emitted from each diode and caused to impinge on the layer of amorphous silicon 5 by propagation in the direction of the multiple upward arrows through bottom glass plate 2b and the layer of conductive Indium Tin Oxide (ITO) 3.
  • ITO Indium Tin Oxide
  • LED light source 4 is controlled by a microprocessor which determines which of the diodes in the array are illuminated at any given time by pre programmed algorithms.
  • the device of the invention may be configured to move a liquid droplet containing a surfactant in an immiscible fluid on a surface by electrodewetting.
  • the liquid droplet may contain surfactant molecules that are mobile in response to an electric field that is applied to the liquid, while the immiscible fluid may contain no surfactant or only surfactants that are not mobile under an electric field in the immiscible fluid (e.g., non-ionic surfactant molecules).
  • an immiscible fluid e.g., air, oil
  • a droplet of liquid e.g., water
  • the surfactant molecules may be cationic surfactant such as cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyl trimethylammonium bromide (DTAB), or anionic surfactant such as 1- hexadecanesulfonic acid sodium salt (HDSAS), sodium tetradecyl sulfate (STS), sodium dodecyl sulfate (SDS), and sodium decyl sulfate (S10S).
  • CAB cetyltrimethylammonium bromide
  • TTAB tetradecyltrimethylammonium bromide
  • DTAB dodecyl trimethylammonium bromide
  • anionic surfactant such as 1- hexadecanesulfonic acid sodium salt (HDSAS), sodium tetradecyl sulfate (STS), sodium dodecyl sulfate (
  • the bromide ion can be altered by other ions such as chloride; in SDS, the sodium ion can be altered by other ions such as potassium ion.
  • concentration of the surfactant should be below its critical micelle concentration (CMC), which is the concentration of a surfactant above which the surfactant molecules form micelles.
  • the photoexcited region 6 reduces the resistivity of a small region of the device and permits a current to flow between the two opposeing electrodes by way of the liquid droplet.
  • this current flow will be mediated by motion of ionic species within the liquid and on the surface of the liquid, and in the case where there is an ionic surfactant on this interface, the current flow will be substantially mediated by the motion of ionic surfactant molecules.
  • This flow of current disperses ionic surfactant molecules away from the surface contact line, thus modifying the contact angle of the droplet at the surface of the photoexcited region 6. Depletion of the surfactant in this region renders the liquid droplet less wetting at this position compared to its natural wetting state.
  • upper conductor layer 3 accumulates surfactant molecules thus also modifying the contact angle of the liquid droplet at the upper conductor layer surface.
  • surfactant molecules are presumed to be cationic surfactant molecules. If an anionic surfactant is used, the droplet would move in the reverse direction. If the bias voltage were to be reversed, the liquid droplet would also move in the reverse direction.
  • any source of DC biasing voltage that provides necessary electrical current supply, such as voltage source, current source, power supply, and their variations, including both manual and programmable sources may be used.
  • the device of the invention can be operated in wetting or dewetting mode. The mode in which the device is operating can be switched by simply reversing the voltage. Whether wetting or dewetting mode is preferable will depend on the contact angle of droplets at the device surface.
  • the surfactant molecules may also be contained in the immiscible carrier fluid outside the droplet.
  • the immiscible carrier fluid may contain surfactant molecules that surround the droplet that sits on a surface of the conductor layers.
  • droplets are mobilised according to the same phenomenon described above.
  • the photoexcited region attracts or disperses surfactant molecules in the immiscible carrier fluid around the contact point with the droplet phase and the device surfaces, thus modifying the contact angle of liquid at the surface of the conductor layer.
  • the upper conductor layer drives surfactant molecules in the opposing direction thus also modifying the contact angle of liquid at the upper conductor layer surface. Because the surrounding immiscible carrier fluid wets the more wetting upper conductor layer and dewets the less wetting photoexcited region, the immiscible carrier fluid moves, carrying the droplet with it.
  • the hydrophilicity of the device surface may be modified by adding another optional thin ( ⁇ 0.1 micron) layer (not shown in Figure 1 ) including a surfactant or by performing a hydrophilic treatment such as piranha solution (a mixture of sulfuric acid and hydrogen peroxide) cleaning or by exposure to oxygen plasma.
  • piranha solution a mixture of sulfuric acid and hydrogen peroxide
  • most hydrophobic surfaces, i.e. , dewettable to water are lipophilic, i.e., wettable to oils.
  • the electrodewetting methods may also work with hydrophobic surfaces if the surfactant- containing liquid (e.g., oil, solvent) wets the hydrophobic surface.
  • the surfactant- containing liquid e.g., oil, solvent
  • the contact angle of the liquid on the surface of interest is less than 90° and increases by more than 10° via surfactant absorption.
  • FIGs. 2 to 4 show a proof-of-concept 2D simulation of the electric field required to generate an effective optoelectrodewetting force, applied to a rectangular droplet using a device of the present invention.
  • an appropriate chosen ionic surfactant appropriate sessile droplet contact angle and appropriate electric field strength for electrodewetting, it follows that an useful level of electrodewetting force will be exerted.
  • a possible approach that can be taken may include the approach of calculating ab- initio the electric field profile which forms around a microdroplet when subjected to a variety of different voltage biases provided by a electrodewetting structure described previously.
  • the calculation is performed by subdividing the layer structure in to units of spatially discrete complex DC permittivity which essentially defines the behaviour of each material to varying electrical biases; behaviour of the photoconductor in response to excitation by light is simulated by a change in the electrical permittivity of those areas of the modelled region which are photoexcited.

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Abstract

L'invention concerne un dispositif et des procédés associés pour manipuler des microgouttelettes par application d'une force d'électrodémouillage qui est à médiation optique. Le dispositif microfluidique est conçu pour manipuler des microgouttelettes, le dispositif comprenant : une première paroi composite comprenant : un premier substrat ; une première couche conductrice sur le premier substrat ; et une couche photoactive sur la première couche conductrice, la couche photoactive ayant une surface hydrophile et une épaisseur inférieure à 150 nm ; une seconde paroi composite comprenant : un second substrat ; une seconde couche conductrice sur le second substrat ; la surface hydrophile de la couche photoactive et la surface exposée de la seconde couche conductrice définissant un espace microfluidique conçu pour contenir des microgouttelettes dans un fluide porteur non miscible, l'un du fluide porteur non miscible et les microgouttelettes contenant un tensioactif ; une source d'alimentation conçue pour fournir une tension aux bornes des première et seconde parois composites ; et une source de rayonnement électromagnétique conçue pour impacter la couche photoactive afin de créer un ou plusieurs emplacements de démouillage sur la couche photoactive, de telle sorte que l'angle de contact d'une ou de plusieurs gouttelettes situées sur ou à proximité des emplacements de démouillage est augmenté.
PCT/GB2020/052606 2019-10-17 2020-10-16 Appareil et procédés de manipulation de microgouttelettes par application d'une force d'électrodémouillage WO2021074635A1 (fr)

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CN113634293A (zh) * 2021-08-09 2021-11-12 复旦大学 一种光控全无机ewod器件
CN115475669A (zh) * 2022-09-15 2022-12-16 上海科技大学 一种液滴微流控芯片
WO2023281275A1 (fr) * 2021-07-09 2023-01-12 Lightcast Discovery Ltd Perfectionnements apportés ou se rapportant à un dispositif microfluidique

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WO2023281275A1 (fr) * 2021-07-09 2023-01-12 Lightcast Discovery Ltd Perfectionnements apportés ou se rapportant à un dispositif microfluidique
CN113634293A (zh) * 2021-08-09 2021-11-12 复旦大学 一种光控全无机ewod器件
CN115475669A (zh) * 2022-09-15 2022-12-16 上海科技大学 一种液滴微流控芯片

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