Directing motion of droplets using differential wetting

Abstract

Apparatus for controlling motion of liquid droplets. A set of electrode pads is arranged to define one or more tracks over which liquid droplets may be induced to move over a sequence of the electrode pads. A surface over the electrode pads is dielectric, smooth, and slippery to the droplets. In some cases, the smooth surface is formed as a thin layer of a second liquid that is immiscible with the liquid of the droplets. The surface has wetting affinity to the liquid that can be individually varied in a controlled manner by application of voltage to respective electrode pads. A control is designed to alter the wetting characteristic of varying-wettability portions of the surface over respective electrode pads to effect induced motion of the droplets over the surface. The apparatus is designed with the smooth hydrophobic surface open, with no overlying or facing electrode or plate above the droplets.

What is claimed is: 
     
         1 .- 30 . (canceled) 
     
     
         31 . A device for processing a droplet comprising a biological sample, comprising:
 an array comprising (i) a plurality of electrodes configured to supply an electric field, (ii) a gap-filling material between one or more adjacent electrodes of said plurality of electrodes, and (iii) a dielectric disposed over said plurality of electrodes and said gap-filling material, wherein said dielectric is distinct from said gap-filling material,   wherein at least a subset of said plurality of electrodes is configured to supply an electric field to alter a wetting characteristic of said dielectric, to thereby manipulate said droplet over said dielectric.   
     
     
         32 . The device of  claim 31 , further comprising a liquid layer disposed over said dielectric. 
     
     
         33 . The device of  claim 32 , wherein said surface of said liquid layer comprises one or more paths, wherein a path of said one or more paths comprises one or more tracks for motion of said droplet. 
     
     
         34 . The device of  claim 32 , wherein said surface of said liquid layer is configured to support an additional droplet comprising an additional sample or a chemical sample. 
     
     
         35 . The device of  claim 32 , wherein said liquid layer comprises an upper surface, and wherein said upper surface of said liquid layer, said droplet, and a gas form a liquid-liquid-gas interface. 
     
     
         36 . The device of  claim 32 , wherein said liquid layer and said dielectric form an electrical barrier between (1) said plurality of electrodes, and (2) said droplet. 
     
     
         37 . The device of  claim 31 , further comprising a light source operatively coupled to said controller, wherein said controller is configured to alter said wetting characteristic of said surface of said liquid layer by directing said light source to apply light to said array. 
     
     
         38 . The device of  claim 31 , further comprising one or more dispensers configured to dispense or remove said droplet to or from said surface. 
     
     
         39 . The device of  claim 31 , wherein said dielectric comprises a polymeric material. 
     
     
         40 . The device of  claim 39 , wherein said polymeric material is removable. 
     
     
         41 . The device of  claim 31 , wherein said array further comprises one or more stations, wherein said one or more stations are selected from the group consisting of a mixing station, a temperature control station, a magnetic field station, an acoustic field station, a nucleic acid delivery station, an optical inspection station, an optical manipulation station, a droplet input station and a droplet output station. 
     
     
         42 . The device of  claim 31 , wherein said dielectric has a thickness of at least 25 nanometers or at most 100 μm. 
     
     
         43 . The device of  claim 31 , wherein said droplet comprises a biological sample. 
     
     
         44 . The device of  claim 31 , wherein said electric field induces said droplet to motion in at least two directions along said surface of said liquid layer. 
     
     
         45 . The device of  claim 31 , further comprising a controller configured to direct said at least a subset of said plurality of electrodes to supply an electric field. 
     
     
         46 . The device of  claim 31 , wherein said gap-filling material comprises a photoresist, epoxy, potting compound, liquid polymer, or dielectric. 
     
     
         47 . The device of  claim 31 , wherein said gap-filling material is a liquid. 
     
     
         48 . A system for processing a biological sample, comprising:
 an array comprising (i) a plurality of electrodes and (ii) a dielectric adjacent to said plurality of electrodes, wherein said dielectric comprises a surface that is configured to support a droplet comprising said biological sample, wherein said plurality of electrodes are configured to supply an electric field to induce said droplet to motion along said surface of said dielectric, wherein said surface has a roughness of less than or equal to 2 micrometer (μm); and   a controller operatively coupled to said plurality of electrodes, wherein said controller is configured to direct at least a subset of said plurality of electrodes to supply an electric field to alter a wetting characteristic of said dielectric adjacent to at least a subset of said plurality of electrodes, to thereby induce said droplet to motion along said dielectric.   
     
     
         49 . The system of  claim 48 , wherein said surface roughness is less than or equal to 0.5 μm. 
     
     
         50 . The system of  claim 48 , wherein said dielectric is textured to hold a layer of a liquid that has a wetting affinity characteristic for said dielectric, wherein said liquid is immiscible with said droplet. 
     
     
         51 . The system of  claim 48 , wherein said surface is configured such that said droplet leaves less trail as compared to a dielectric with a roughness of greater than 2 μm. 
     
     
         52 . The system of  claim 48 , wherein said surface is configured to support a subsequent droplet, wherein said subsequent droplet is not subject to cross contamination from said droplet. 
     
     
         53 . The system of  claim 48 , wherein said dielectric comprises one or more paths, wherein a path of said one or more paths comprises one or more tracks for motion of said droplet. 
     
     
         54 . The system of  claim 48 , wherein said dielectric is configured to support one or more additional droplets comprising an additional biological sample or a chemical sample. 
     
     
         55 . The system of  claim 48 , wherein said surface is hydrophobic. 
     
     
         56 . The system of  claim 48 , further comprising one or more dispensers configured to dispense or remove said one or more droplets to and from said surface. 
     
     
         57 . The system of  claim 48 , wherein said dielectric comprises a polymeric film. 
     
     
         58 . The system of  claim 57 , wherein said polymeric film is removable. 
     
     
         59 . The system of  claim 48 , wherein further comprising an additional plurality of electrodes and wherein said plurality of electrodes and said additional plurality of electrodes are not coplanar. 
     
     
         60 . The system of  claim 48 , wherein said array further comprises one or more stations, wherein said one or more stations are selected from the group consisting of a mixing station, a temperature control station, a magnetic field station, an acoustic field station, a nucleic acid delivery station, an optical inspection station, optical manipulation station, droplet input station and droplet output station.