Manipulation of beads in droplets and methods for manipulating droplets
Provided herein are methods of splitting droplets containing magnetically responsive beads in a droplet actuator. A droplet actuator having a plurality of droplet operations electrodes configured to transport the droplet, and a magnetic field present at the droplet operations electrodes, is provided. The magnetically responsive beads in the droplet are immobilized using the magnetic field and the plurality of droplet operations electrodes are used to split the droplet into first and second droplets while the magnetically responsive beads remain substantially immobilized.
1. A method of splitting a droplet comprising magnetically responsive beads, the method comprising:
(a) providing a droplet actuator comprising:
(i) a plurality of droplet operations electrodes configured to transport the droplet; and
(ii) a magnetic field present at the plurality of droplet operations electrodes;
(b) substantially immobilizing the magnetically responsive beads using the magnetic field; and
(c) using the plurality of droplet operations electrodes to split the droplet into first and second droplets, wherein the first droplet contains at least substantially all of the magnetically responsive beads and the second droplet is at least substantially lacking in magnetically responsive beads.
2. The method of claim 1 further wherein the splitting involves using a hydrophilic patch.
3. The method of claim 1 further comprising using a magnet to generate the magnetic field.
4. The method of claim 1 further comprising using a magnet embedded within a gasket of the droplet actuator to generate the magnetic field.
5. The method of claim 1 further comprising positioning a magnet proximate a gasket of the droplet actuator to generate the magnetic field.
6. The method of claim 1 further comprising using a physical barrier to facilitate splitting of the droplet.
7. The method of claim 1 further comprising using a magnetized physical barrier to facilitate splitting of the droplet.
8. The method of claim 1 further comprising positioning a magnetic shielding material in the droplet actuator to selectively minimize the magnetic field.
9. The method of claim 1 wherein the magnetic field is sufficiently strong to hold the magnetically responsive beads substantially immobile during a droplet operation.
10. The method of claim 1 wherein the magnetic field is sufficiently weak to enable the magnetically responsive beads to be moved away from the magnetic field during a droplet operation.
11. The method of claim 1 wherein the droplet operations electrodes comprise an electrode path having a droplet splitting region, the droplet splitting region including a segmented electrode comprising a plurality of electrode strips, including inner electrode strips and outer electrode strips, wherein the electrode strips can be independently activated and deactivated to cause the controlled splitting of the droplet in the droplet splitting region.
12. The method of claim 11 wherein the droplet is split into first and second droplets by:
(i) activating the droplet operations electrodes to extend a droplet across the electrode strips of the segmented electrode; and
(ii) causing the controlled splitting of the droplet in the droplet splitting region by either deactivating the inner electrode strips followed by deactivating the outer electrode strips, or by deactivating the outer electrode strips followed by deactivating the inner electrode strips.
13. The method of claim 1 wherein the droplet operations electrodes comprise an electrode path having a droplet splitting region, the droplet splitting region including a tapered electrode that has a length along the electrode path that is about twice that of an adjacent droplet operations electrode.
14. The method of claim 1 wherein the droplet operations electrodes comprise an electrode path having a droplet splitting region, the droplet splitting region including two adjacent tapered electrodes that have a combined length along the electrode path that is about three times that of an adjacent droplet operations electrode.
15. The method of claim 1 wherein the droplet operations electrodes comprise an electrode path having a droplet splitting region, the droplet splitting region including a segmented electrode comprising multiple rows and columns of electrode strips that can be independently activated and deactivated to cause the controlled splitting of the droplet in the droplet splitting region.
16. The method of claim 1 further comprising:
(i) a bottom substrate having a droplet operations surface comprising the droplet operations electrodes;
(ii) a top substrate separated from the droplet operations surface to form a gap; and
(iii) a physical barrier extending from the top substrate into the gap and constricting the gap in proximity with the one or more droplet operations electrodes.
17. The method of claim 16 wherein the barrier produces a magnetic field.
18. The method of claim 16 further comprising a first electromagnet arranged near the top substrate of the droplet actuator and a second electromagnet arranged near the bottom substrate of the electromagnet.
19. The method of claim 18 further comprising using the first electromagnet and second electromagnet to disperse the magnetically responsive beads within the droplet by switching on and off the magnetic field produced by the first electromagnet and second electromagnet.