Method of detecting an analyte
The invention relates to certain novel approaches to reducing or eliminating the movement of contaminants from one droplet to another on a droplet actuator via liquid filler fluid. In one application, a method of detecting an analyte is provided and includes providing in a detection window a droplet including a signal-producing substance indicative of the presence and/or quantity of an analyte and one or more magnetically responsive beads which may interfere with signal produced by the signal producing substance. The method further includes using a magnetic field for magnetically removing the magnetically responsive beads from the detection window and/or magnetically restricting the magnetically responsive beads from entering the detection window while transporting and/or retaining the droplet in the detection window. The method additionally includes detecting a signal produced by the signal-producing substance.
1. A method of detecting an analyte, the method comprising:
(a) providing a droplet in a droplet operations gap of a droplet actuator in a detection window comprising an opening or window in a substrate of the droplet actuator, the droplet comprising:
(i) a signal-producing substance indicative of the presence and/or quantity of an analyte;
(ii) one or more magnetically responsive beads which may interfere with signal produced by the signal producing substance;
(b) using a magnetic field for:
(i) magnetically removing the magnetically responsive beads from the detection window, wherein the magnetic field aggregates the magnetically responsive beads in a region of the droplet which is outside the detection window; and/or
(ii) magnetically restricting the magnetically responsive beads from entering the detection window while transporting and/or retaining the droplet in the detection window, wherein the magnetic field aggregates the magnetically responsive beads in a region of the droplet which is outside the detection window;
(c) detecting a signal from the droplet within the detection window produced by the signal-producing substance to detect the presence, absence and/or quantity of the analyte while the magnetically responsive beads are outside the detection window.
2. The method of claim 1 wherein,
step 1(b) comprises providing a fixed magnet in proximity to the detection window; and
transporting the droplet into the detection window delivers the magnetically responsive beads into sufficient proximity with the fixed magnet that the beads are pulled away from and/or restricted from entering the detection window.
3. The method of claim 1 wherein the magnetic field is generated by a magnetic field source comprising a fixed permanent magnet.
4. The method of claim 1 wherein the magnetic field is generated by a magnetic field source comprising a moveable permanent magnet.
5. The method of claim 1 wherein the magnetic field is generated by a magnetic field source comprising an electromagnet.
6. The method of claim 1 wherein the magnetic field aggregates the magnetically responsive beads at an edge of the droplet.
7. The method of claim 1 wherein the signal is produced by a fluorescent dye.
8. The method of claim 1 wherein the magnetic field attracts the magnetically responsive beads in a manner which restricts substantially all of the beads from entering or re-entering the detection window as the droplet is transported into the detection window.
9. The method of claim 1 wherein the detection window is provided in a substrate of a droplet actuator device.
10. The method of claim 9 wherein the droplet actuator comprises a plurality of paths of electrodes associated with the droplet operations substrate, each path associated with
a detection window; and
a magnetic field in proximity to the path, the magnetic field arranged for:
(i) magnetically removing the magnetically responsive beads from the corresponding detection window; and/or
(ii) magnetically restricting the magnetically responsive beads from entering the corresponding detection window while transporting into and/or retaining the droplet in the detection window.
11. The method of claim 1 wherein the one or more analytes comprise amplified nucleic acid.
12. The method of claim 1 wherein,
the detection window is located in a substrate of a droplet actuator;
the droplet actuator comprises temperature control zones along the path of electrodes for conducting a thermal cycling reaction; and
the method comprises:
(i) thermal cycling an amplification-ready droplet to yield an amplified droplet; and
(ii) transporting the amplified droplet into the detection window.
13. The method of claim 12 comprising transporting a droplet comprising magnetically responsive beads along the path of electrodes to the path of electrodes at least partially into the detection window following 1 or more of the thermal cycles.
14. The method of claim 1 wherein the droplet is retained in place in the detection window by electrowetting while the magnetic field aggregates the magnetically responsive beads in a region of the droplet which is outside the detection window.