Droplet interfaces in electro-wetting devices
Droplet interfaces are formed between droplets in an electro-wetting device comprising an array of actuation electrodes. Actuation signals are applied to selected actuation electrodes to place the droplets into an energised state in which the shape of the droplets is modified compared to a shape of the droplets in a lower energy state and to bring the two droplets into proximity. The actuation signals are then changed to lower the energy of the droplets into the lower energy state so that the droplets relax into the gap and the two droplets contact each other thereby forming a droplet interface. The use of sensing electrodes in the device permit electrical current measurements across the droplet interface. The sensing electrodes can be used for either (i) applying a reference signal during droplet actuation or (ii) recording electrical current measurements.
1. An apparatus for performing experiments on droplet interfaces, the apparatus comprising:
an electro-wetting device comprising an array of actuation electrodes and an electrically insulating layer covering the actuation electrodes and having an outermost hydrophobic surface of the electrically insulating layer, the electro-wetting device being arranged to receive a fluid medium and droplets comprising liquid in the fluid medium disposed on the hydrophobic surface,
a control system configured to apply actuation signals to the actuation electrodes selected to manipulate received droplets and to form at least one system of droplets having one or more droplet interfaces between the droplets; and
a sensor system configured to take electrical measurements between droplets in at least one formed system of droplets across droplet interfaces;
wherein the sensor system comprises a substrate supporting at least two sensor electrodes facing the hydrophobic surface of the electrically insulating layer;
wherein the substrate comprises a hydrophobic material coating, the hydrophobic material coating having apertures exposing only a part of the sensor electrodes.
2. An apparatus according to claim 1 , wherein the control system is arranged to modify the at least one formed system of droplets in response to outputs of the sensor system.
3. An apparatus according to claim 2 , wherein said outputs of the sensor system include electrical measurements taken by the sensor system.
4. An apparatus according to claim 2 , wherein the sensor system further comprises an analysis system configured to process the electrical measurements, and said outputs of the sensor system include outputs of the analysis system.
5. An apparatus according to claim 2 , wherein the control system is configured to apply actuation signals to the actuation electrodes selected to modify the at least one formed system of droplets by separating a droplet interface in the system.
6. An apparatus according to claim 2 , wherein the control system is configured to apply actuation signals to the actuation electrodes selected to modify the at least one formed system of droplets by moving a new droplet into contact with a current droplet in the system of droplets and forming a droplet interface between the new droplet and the current droplet.
7. An apparatus according to claim 2 , wherein the control system is configured to apply actuation signals to the actuation electrodes selected to modify the at least one formed system of droplets by moving a new droplet into contact with a current droplet in the system of droplets and fusing the new droplet and the current droplet.
8. An apparatus according to claim 7 , wherein the new droplet does not comprise amphipathic molecules at the interface between the liquid of the droplet and the fluid medium.
9. An apparatus according to claim 1 , wherein the control system is configured to apply actuation signals to the actuation electrodes selected to form plural systems of droplets in parallel.
10. An apparatus according to claim 1 , wherein the control system is configured to apply actuation signals to the actuation electrodes selected to form at least one system of droplets having one or more droplet interfaces between the droplets.
11. An apparatus according to claim 1 , wherein the electrical measurements include impedance measurements.
12. An apparatus according to claim 1 , wherein the sensor system is configured to take electrical measurements in a frequency range from a lower limit to an upper limit, wherein the lower limit is 1 Hz, 10 Hz or 100 Hz and the upper limit is 10 MHz, 100 KHz or 10 KHz, in any combination.
13. An apparatus according to claim 1 , wherein the electrical measurements are measurements of ion flow between droplets through a transmembrane pore.
14. An apparatus according to claim 1 , wherein the sensor system is arranged to take the electrical measurements while applying a potential difference between a respective pair of sensor electrodes.
15. An apparatus according to claim 1 , wherein the sensor system further comprises an analysis system configured to process the electrical measurements.
16. An apparatus according to claim 15 , wherein the analysis system is configured to process the electrical measurements to analyse an analyte that interacts with a transmembrane pore inserted into a formed droplet interface comprising a membrane of amphipathic molecules.
17. An apparatus according to claim 16 , wherein the analyte is a polymer comprising polymer units and the sensor system is configured to process the electrical measurements to derive estimated identities of polymer units of the polymer.
18. An apparatus according to claim 1 , further comprising a droplet preparation system configured to form droplets disposed on the hydrophobic surface of the electro-wetting device in the fluid medium, wherein the control system is configured to control the droplet preparation system to form the droplets.
19. An apparatus according to claim 1 , wherein the insulator layer comprises a layer of electrically insulating material coated by a hydrophobic material that forms said hydrophobic surface.