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. Two or more electrodes are configurable to lyse cells within a droplet positioned over said electrodes.
1. An apparatus for receiving a droplet having a sample and for lysing said sample to perform experiments on the sample using a plurality of droplet interfaces, the apparatus comprising:
an electro-wetting device comprising:
an array of actuation electrodes and an insulator layer covering the actuation electrodes supported on a first substrate and having an outermost hydrophobic surface, 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;
an array of sensor electrodes coated by a hydrophobic material, said hydrophobic material comprising apertures configured to expose at least part of the sensor electrodes supported on a second substrate, such that the droplets are sandwiched between the first and second substrate;
a lyser, connected to at least two lysing electrodes, and configured to apply a lysing signal to a droplet for lysing a cell within a droplet, wherein the lysing signal is controlled by the control system; and
a sensor system configured to take electrical measurements between droplets in a formed system of droplets across droplet interfaces.
2. An apparatus according to claim 1 wherein the at least two lysing electrodes are measurement electrodes or actuation electrodes.
3. An apparatus according to claim 1 , wherein the actuation electrodes in the array of actuation electrodes are individually controllable and the control system is configured to pass a lysing signal via a droplet positioned between or over any two actuation electrodes in the array of actuation electrodes.
4. An apparatus according to claim 1 , wherein at least two actuation electrodes in the array of actuation electrodes are operable as lysing electrodes configured to provide the lysing signal, and wherein the lysing electrodes are isolated mechanically and/or electrically from the other electrodes in the array of actuation electrodes, and wherein the array of actuation electrodes is configured to manoeuvre a droplet having a sample to and from the lysing electrodes.
5. An apparatus according to claim 1 , wherein two lysing electrodes are configured in a lysing zone adjacent or within the array of actuation electrodes, said lysing zone isolated from the array of actuation electrodes, and wherein the array of actuation electrodes is configured to manoeuvre a droplet having a sample to and from the lysing zone.
6. An apparatus according to claim 1 , wherein the control system is configured to deactivate and/or isolate the array of actuation electrodes from two or more electrodes in the array of actuation electrodes that operate as lysing electrodes for a period of time during which a lysing signal is applied to a droplet for lysing a cell within a droplet.
7. An apparatus according to claim 6 , wherein a ratio between
the length of time that the control system isolates the array of actuation electrodes, and
the length of time a lysing signal is applicable to a droplet, is between about 20:1 and about 2:1 in units of seconds:seconds.
8. An apparatus according to claim 1 , wherein the second substrate supports at least one lysing electrode.
9. An apparatus according to claim 1 , wherein the apparatus is configured to:
receive a droplet having a sample to be analyzed;
manoeuvre the droplet to the at least two lysing electrodes for lysing said sample for rupturing cells therein;
manoeuvre at least a portion of the lysed droplet to a measurement electrode;
move a second droplet adjacent the lysed droplet to form a droplet interface bilayer; and
perform measurements on the sample using the droplet interface.
10. An apparatus according to claims 9 , wherein following lysing, the apparatus moves and/or mixes the lysed sample for preparation before creating a droplet interface bilayer and subsequent experiments.
11. An apparatus according to claim 9 , wherein after manoeuvring the droplet to lysing electrodes the apparatus is further configured to collate content of the droplet in a group using dielectrophoresis such that the group of contents are arranged for lysing for rupturing cells therein.
12. An apparatus according to claim 11 configured to apply the dielectrophoresis field between the lysing electrodes.
13. An apparatus according to claim 3 , wherein the electrical measurements are measurements of ion flow between droplets through a transmembrane pore.
14. An apparatus according to claim 3 , wherein the sensor system further comprises an analysis system configured to process the electrical measurements, and wherein the analysis system is configured to process the electrical measurements to analyze an analyte that interacts with a transmembrane pore inserted into a formed droplet interface comprising a membrane of amphipathic molecules, and 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.
15. An apparatus according to claim 3 , wherein the electro-wetting device is arranged to receive droplets comprising amphipathic molecules at their surface and containing a transmembrane pore and 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 comprising a membrane of amphipathic molecules between the droplets such that a transmembrane pore is allowed to insert into a formed droplet interface.
16. A method for preparing an analyte in an apparatus according to claim 1 , the method comprising:
contacting a first droplet containing a cell of interest with at least two actuation electrodes, said electrodes connectable to the lyser for applying a lysing signal to the first droplet to lyse said cell;
connecting the lyser to an electrode pair of the at least two actuation electrodes in contact with the first droplet to lyse the cell and release analyte of interest from the cell.
17. The method of claim 16 , further comprising using dielectrophoresis to group cells within the droplet prior to lysing.
18. The method of claim 17 , wherein the dielectrophoresis is applied between the lysing electrodes in order to group the cells at the lysing electrodes for lysing.
19. The method of claim 18 , wherein following lysing of the cells and release of the analyte into the droplet, a further dielectrophoresis field is applied to the droplet to hold the analyte at the at least two lysing electrodes.
20. The method of claim 16 , further including:
dividing the first droplet to form a first sub-droplet and a second sub-droplet to form a first droplet pair;
bringing a second droplet in to contact with the first sub-droplet to form a second droplet pair and contacting each of the first sub-droplet and the second droplet with a respective measurement electrode; and
bringing a third droplet in to contact with the second sub-droplet to form a third droplet pair and contacting each of the second sub-droplet and third droplet with a respective measurement electrode.