MICRODROPLET MANIPULATION DEVICE

Abstract

A device for manipulating microdroplets using optically-mediated electrowetting comprising: a first composite wall comprising: a first transparent substrate; a first transparent conductor layer on the substrate having a thickness of 70 to 250 nm; a photoactive layer activated by electromagnetic radiation in the wavelength range 400-1000 nm on the conductor layer having a thickness of 300-1000 nm; and a first dielectric layer on the conductor layer having a thickness of 120-160 nm; a second composite wall comprised of: a second substrate; a second conductor layer on the substrate having a thickness of 70 to 250 nm; and an A/C source to provide a voltage across the first and second composite walls connecting the first and second conductor layers; at least one source of electromagnetic radiation having an energy higher than the bandgap of the photoexcitable layer; and means for manipulating the points of impingement of the electromagnetic radiation on the photoactive layer.

Claims

1. A device for manipulating microdroplets using optically-mediated electrowetting consisting essentially of: a first composite wall comprising: a first substrate; a first transparent conductor layer on the first substrate having a thickness in the range 70 to 250 nm; a photoactive layer activated by electromagnetic radiation in the wavelength range 400-1000 nm on the first transparent conductor layer having a thickness in the range 300-1000 nm and a first dielectric layer on the photoactive layer having a thickness in the range 120 to 160 nm; a second composite wall comprising: a second substrate; a second conductor layer on the second substrate having a thickness in the range 70 to 250 nm; and optionally a second dielectric layer on the second conductor layer having a thickness in the range 120 to 160 nm wherein exposed surfaces of the first and second dielectric layers are disposed less than 10 m apart to define a microfluidic space adapted to contain microdroplets; an A/C source to provide a voltage across the first and second composite walls connecting the first and second conductor layers; at least one source of electromagnetic radiation having an energy higher than the bandgap of a photoexcitable layer adapted to impinge on the photoactive layer to induce corresponding ephemeral electrowetting locations on the surface of the first dielectric layer; and means for manipulating the points of impingement of the electromagnetic radiation on the photoactive layer so as to vary the disposition of the ephemeral electrowetting locations thereby creating at least one electrowetting pathway along which microdroplets may be caused to move.

2. The device as claimed in claim 1, wherein the first and second composite walls further comprise first and second anti-fouling layers on respectively the first and second dielectric layers.

3. The device as claimed in claim 2, wherein the anti-fouling layer on the second dielectric layer is hydrophobic.

4. The device as claimed in claim 1, wherein the microfluidic space is further defined by a spacer attached to the first and second dielectric layers.

5. The device as claimed in claim 1, wherein the electrowetting pathway is comprised of a continuum of virtual electrowetting locations each subject to ephemeral electrowetting at some point during use of the device.

6. The device as claimed in claim 1, wherein the microfluidic space is from 2 to 8 m.

7. The device as claimed in claim 1, wherein the source(s) of electromagnetic radiation comprise a pixellated array or light reflected from or transmitted through such an array.

8. The device as claimed in claim 1, wherein the electrowetting locations are crescent-shaped in the direction of travel of the microdroplets.

9. The device as claimed in claim 1, further comprising a means to stimulate and detect fluorescence in the microdroplets located within or downstream of the device.

10. The device as claimed in claim 1, further comprising a means to generate a medium comprised of an emulsion of aqueous microdroplets in an immiscible carrier fluid.

11. The device as claimed in claim 1, further comprising a means to induce a flow of a medium comprised of an emulsion of aqueous microdroplets in an immiscible carrier fluid through the microfluidic space via an inlet into the microfluidic space.

12. The device as claimed in claim 1, wherein the first and second composite walls are first and second composite sheets which define the microfluidic space therebetween and form the periphery of a cartridge or chip.

13. The device as claimed in claim 12, further comprising a plurality of first electrowetting pathways running concomitantly to each other.

14. The device as claimed in claim 13, further comprising a plurality of second electrowetting pathways adapted to intersect with the first electrowetting pathways to create at least one microdroplet-coalescing location.

15. The device as claimed in claim 1, further comprising a means for introducing into the microfluidic space microdroplets whose diameters are more than 20% greater than the width of the microfluidic space.

16. The device as claimed in claim 1, wherein the second composite wall further comprises a second photoexcitable layer and the source of electromagnetic radiation also impinges on the second photoexcitable layer to create a second pattern of ephemeral electrowetting locations which can also be varied.

17. The device as claimed in claim 1, where spacers are used to control the spacing between the first and second layer structures, and the physical shape of these spacers is used to aid the splitting, merging and elongation of the microdroplets in the device

18. A method for manipulating aqueous microdroplets comprising the steps of (a) introducing an emulsion of the microdroplets in an immiscible carrier medium into a microfluidic space having a defined by two opposed walls spaced less than 10 m or less apart and respectively comprising: a first composite wall comprising: a first transparent substrate a first transparent conductor layer on the first transparent substrate having a thickness in the range 70 to 250 nm; a photoactive layer activated by electromagnetic radiation in the wavelength range 400-1000 nm on the first transparent conductor layer having a thickness in the range 300-1000 nm and a first dielectric layer on the first transparent conductor layer having a thickness in the range 120 to 160 nm; a second composite wall comprising: a second substrate; a second conductor layer on the second substrate having a thickness in the range 70 to 250 nm and optionally a second dielectric layer on the second conductor layer having a thickness in the range 120 to 160 nm; (b) applying a plurality of point sources of the electromagnetic radiation to the photoactive layer to induce a plurality of corresponding ephemeral electrowetting locations in the first dielectric layer; and (c) moving a least one of the microdroplets in the emulsion along an electrowetting pathway created by the ephemeral electrowetting locations by varying the application of the point sources to the photoactive layer.

Description

[0046] The invention is now illustrated by the following.

[0047] FIG. 1 shows a cross-sectional view of a device according to the invention suitable for the fast manipulation of aqueous microdroplets 1 emulsified into a hydrocarbon oil having a viscosity of 5 centistokes or less at 25 C. and which in their unconfined state have a diameter of less than 10 m (e.g. in the range 4 to 8 m). It comprises top and bottom glass plates (2a and 2b) each 500 m thick coated with transparent layers of conductive Indium Tin Oxide (ITO) 3 having a thickness of 130 nm. Each of 3 is connected to an A/C source 4 with the ITO layer on 2b being the ground. 2b is coated with a layer of amorphous silicon 5 which is 800 nm thick. 2a and 5 are each coated with a 160 nm thick layer of high purity alumina or Hafnia 6 which are in turn coated with a monolayer of poly(3-(trimethoxysilyl)propyl methacrylate) 7 to render the surfaces of 6 hydrophobic. 2a and 5 are spaced 8 m apart using spacers (not shown) so that the microdroplets undergo a degree of compression when introduced into the device. An image of a reflective pixelated screen, illuminated by an LED light source 8 is disposed generally beneath 2b and visible light (wavelength 660 or 830 nm) at a level of 0.01 Wcm.sup.2 is emitted from each diode 9 and caused to impinge on 5 by propagation in the direction of the multiple upward arrows through 2b and 3. At the various points of impingement, photoexcited regions of charge 10 are created in 5 which induce modified liquid-solid contact angles in 6 at corresponding electrowetting locations 11. These modified properties provide the capillary force necessary to propel the microdroplets 1 from one point 11 to another. 8 is controlled by a microprocessor 12 which determines which of 9 in the array are illuminated at any given time by pre-programmed algorithms.

[0048] FIG. 2 shows a top-down plan of a microdroplet 1 located on a region of 6 on the bottom surface bearing a microdroplet 1 with the dotted outline 1a delimiting the extent of touching. In this example, 11 is crescent-shaped in the direction of travel of 1.