Methods for Manipulating Droplets by Electrowetting-Based Techniques

• US 20090260988A1
• Filed: 06/30/2009
• Published: 10/22/2009
• Est. Priority Date: 09/24/2002
• Status: Active Grant

• Current Assignee: Duke University
• Original Assignee: Duke University
• Inventors: Pamula, Vamsee K., Ren, Hong, Paik, Philip Y., Pollack, Michael G., Fair, Richard B.
• Granted Patent: US 8,394,249 B2
• Time in Patent Office: Days
• US Class Current: 204/450
• CPC Class Codes: B01F 31/65 the materials to be mixed being directly submitted to a pulsating movement, e.g. by means of an oscillating piston or air column
• CPC Class Codes: B01F 33/3021 the components to be mixed being combined in a single independent droplet, e.g. these droplets being divided by a non-miscible fluid or consisting of independent droplets
• CPC Class Codes: B01F 33/3031 using electro-hydrodynamic [EHD] or electro-kinetic [EKI] phenomena to mix or move the fluids
• CPC Class Codes: B01F 33/30351 using hydrophilic/hydrophobic surfaces
• CPC Class Codes: B01L 2200/06 Fluid handling related problems
• CPC Class Codes: B01L 2200/0605 Metering of fluids
• CPC Class Codes: B01L 2200/10 Integrating sample preparation and analysis in single entity, e.g. lab-on-a-chip concept
• CPC Class Codes: B01L 2300/089 Virtual walls for guiding liquids
• CPC Class Codes: B01L 2300/161 Control and use of surface tension forces, e.g. hydrophobic, hydrophilic
• CPC Class Codes: B01L 2300/165 Specific details about hydrophobic, oleophobic surfaces
• CPC Class Codes: B01L 2400/0415 electrical forces, e.g. electrokinetic
• CPC Class Codes: B01L 2400/0427 Electrowetting
• CPC Class Codes: B01L 3/00 Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
• CPC Class Codes: B01L 3/5027 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 B01L3/5023 takes precedence; micromixers B01F33/30; microreactors for synthesis B01J19/0093; microcapillary devices in general B81B1/00
• CPC Class Codes: B01L 3/50273 characterised by the means or forces applied to move the fluids micropumps F04B19/006, of the membrane type F04B43/043
• CPC Class Codes: B01L 3/502784 specially adapted for droplet or plug flow, e.g. digital microfluidics automatic analysis using a stream of discrete samples in a tube system G01N35/08
• CPC Class Codes: B01L 3/502792 for moving individual droplets on a plate, e.g. by locally altering surface tension
• CPC Class Codes: B41J 2002/14395 Electrowetting
• CPC Class Codes: C25B 9/00 Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
• CPC Class Codes: G01N 27/44791 Microapparatus sample containers with integrated microfluidic structures B01L3/5027
• CPC Class Codes: G02B 26/005 : based on electrowetting

Abstract

Methods are provided for manipulating droplets. The methods include providing the droplet on a surface comprising an array of electrodes and a substantially co-planer array of reference elements, wherein the droplet is disposed on a first one of the electrodes, and the droplet at least partially overlaps a second one of the electrodes and an intervening one of the reference elements disposed between the first and second electrodes. The methods further include activating the first and second electrodes to spread at least a portion of the droplet across the second electrode and deactivating the first electrode to move the droplet from the first electrode to the second electrode.

Claims

1. A method for actuating a droplet comprising the steps of:

(a) providing the droplet on a surface comprising an array of electrodes and an array of one or more reference elements, wherein the droplet is disposed on a first one of the electrodes, and the droplet is adjacent to a second one of the electrodes; and

(b) biasing the first and second electrodes to move the droplet from the first electrode to the second electrode.

2. The method according to claim 1 wherein the second electrode is adjacent to the first electrode along a first direction, the electrode array comprises one or more additional electrodes adjacent to the first electrode along one or more additional directions, the droplet is adjacent to the one or more additional electrodes, and the method comprises the steps of:

(a) selecting the first direction as a desired direction along which the droplet is to move; and

(b) selecting the second electrode for biasing based on the selection of the first direction.

3. A method for splitting a starting droplet into two or more droplets, comprising the steps of:

(a) providing a starting droplet on a surface of a substrate, the substrate comprising an array of drive electrodes, wherein the drive electrode array comprises at least three drive electrodes comprising a first outer drive electrode, a medial drive electrode adjacent to the first outer drive electrode, and a second outer drive electrode adjacent to the medial drive electrode, and the starting droplet is initially disposed on at least one of the three drive electrodes and is adjacent to at least one other of the three drive electrodes;

(b) biasing each of the three drive electrodes to a first voltage to position the starting droplet across the three drive electrodes; and

(c) biasing the medial drive electrode to a second voltage different from the first voltage to split the starting droplet into first and second split droplets, whereby the first split droplet is formed on the first outer drive electrode and the second split droplet is formed on the second outer drive electrode; and

wherein the substrate further comprises a grounded electrode, and the droplet overlaps the grounded electrode.

4. The method according to claim 3 wherein the step of biasing the three drive electrodes to the first voltage comprises selectively coupling the three drive electrodes with a voltage source.

5. The method according to claim 3 wherein the second voltage is approximately zero.

6. A method for merging two or more droplets into one droplet, comprising the steps of:

(a) providing first and second droplets on a surface comprising an array of electrodes, wherein the electrode array comprises at least three electrodes comprising a first outer electrode, a medial electrode adjacent to the first outer electrode, and a second outer electrode adjacent to the medial electrode, the first droplet is disposed on the first outer electrode and is adjacent to the medial electrode, and the second droplet is disposed on the second outer electrode and is adjacent to the medial electrode;

(b) selecting one of the three electrodes as a destination electrode;

(c) selecting two or more of the three electrodes for biasing based on the selection of the destination electrode; and

(d) biasing the electrodes selected between a first voltage and a second voltage to move one of the first and second droplets toward the other droplet or both of the first and second droplets toward each other, whereby the first and second droplets merge together to form a combined droplet on the destination electrode.

7. The method according to claim 6 wherein the first outer electrode is selected as the destination electrode, and the biasing step comprises biasing the second outer electrode and the medial electrode to the first voltage to position the second droplet across the medial electrode, biasing the second outer electrode to the second voltage to move the second droplet away from the second outer electrode, biasing the first outer electrode to the first voltage to merge the first and second droplets into each other, and biasing the medial electrode to the second voltage to form the combined droplet on the first outer electrode.

8. The method according to claim 6 wherein the second outer electrode is selected as the destination electrode, and the biasing step comprises biasing the first outer electrode and the medial electrode to the first voltage to position the first droplet across the medial electrode, biasing the first outer electrode to the second voltage to move the first droplet away from the first outer electrode, biasing the second outer electrode to the first voltage to merge the first and second droplets into each other, and biasing the medial electrode to the second voltage to form the combined droplet on the second outer electrode.

9. The method according to claim 6 wherein the medial electrode is selected as the destination electrode, and the biasing step comprises biasing the first outer electrode, the medial electrode, and the second outer electrode to the first voltage to position the first and second droplets across the medial electrode and to merge the first and second droplets into each other, and biasing the first and second outer electrodes to the second voltage to move the first and second droplets away from the first and second outer electrodes, respectively, and form the combined droplet on the medial electrode.

10. The method according to claim 6 comprising the step of sequentially biasing other electrodes of the electrode array to move the first droplet into electrical communication with the first outer electrode prior to forming the combined droplet.

11. The method according to claim 6 wherein the second voltage is approximately zero.

12. The method according to claim 6 wherein the first droplet comprises a first composition, the second droplet comprises a second composition, and the combined droplet comprises the first and second compositions, the method further comprising the step of mixing the first and second compositions together.

13. The method according to claim 12 wherein the step of forming the combined droplet mixes the first and second compositions together.

14. The method according to claim 12 wherein the mixing step comprises passively mixing the first and second compositions together by allowing diffusion to occur within the combined droplet.

15. The method according to claim 12 wherein the mixing step comprises moving the combined droplet on a two-by-two sub-array of four electrodes by sequentially biasing each of the four electrodes to rotate the combined droplet.

16. The method according to claim 15 wherein at least a portion of the combined droplet remains substantially stationary at or near an intersecting region of the four electrodes while the combined droplet rotates.

17. The method according to claim 12 wherein the mixing step comprises sequentially activating and de-activating a linearly arranged set of electrodes of the electrode array to oscillate the combined droplet back and forth along the linearly arranged electrode set a desired number of times and at a desired frequency.

18. The method according to claim 12 wherein the mixing step comprises selecting a set of electrodes of the electrode array as mixing electrodes, and biasing one or more of the mixing electrodes to split the combined droplet into two or more split droplets and oscillate the split droplets along one or more linear paths a desired number of times and at a desired frequency.

19. The method according to claim 18 comprising the step of merging the split droplets to form a new combined droplet.

20. The method according to claim 19 comprising the steps of splitting the new combined droplet into two or more new split droplets and oscillating the new split droplets.

21. The method according to claim 12 wherein the mixing step comprises selecting a set of electrodes of the electrode array as transport electrodes, and sequentially biasing one or more of the transport electrodes to actuate the combined droplet along a transport path defined by the transport electrodes, whereby the first and second compositions of the combined droplet become mixed together as the combined droplet moves along the transport path.

22. The method according to claim 21 wherein the transport path comprises a repeatable loop on the electrode array, and the combined droplet is actuated along the loop a desired number of times.

23. The method according to claim 12 wherein the mixing step comprises selecting a set of electrodes of the electrode array as mixing electrodes, and sequentially biasing one or more of the mixing electrodes to split the combined droplet into two or more split droplets and move the split droplets along two or more paths.