Manipulation of beads in droplets and methods for manipulating droplets
The invention provides a method of circulating magnetically responsive beads within a droplet in a droplet actuator. The invention also provides methods for splitting droplets. The invention, in one embodiment, makes use of a droplet actuator with top and bottom substrates, a plurality of magnetic fields respectively present proximate the top and bottom substrates, wherein at least one of the magnet fields is selectively alterable, and a plurality of droplet operations electrodes positioned along at least one of the top and bottom surfaces. A droplet is positioned between the top and bottom surfaces and at least one of the magnetic fields is selectively altered.
1. A method of dispensing a bead-containing sub-droplet, the method comprising:
(a) circulating magnetically responsive beads within a droplet on a droplet actuator, wherein circulating comprises:
(i) providing a droplet actuator, comprising:
(1) top and bottom substrates;
(2) a plurality of magnetic fields respectively present proximate the top and bottom substrates, wherein at least one of the magnet fields is selectively alterable; and
(3) a plurality of droplet operations electrodes positioned along at least one of the top and bottom surfaces;
(ii) positioning the droplet comprising magnetically responsive beads between the top and bottom substrates in a gap that is within the magnetic fields; and
(iii) selectively altering at least one of the magnetic fields to circulate the magnetically responsive beads in the droplet; and
(b) using droplet operations to dispense a sub-droplet from the droplet.
2. The method of claim 1 wherein altering at least one of the magnetic fields further comprises activating an electromagnet proximate at least one of the top and bottom surfaces.
3. The method of claim 1 wherein altering at least one of the magnetic fields further comprises activating and deactivating the magnetic fields in a pattern which causes the beads to circulate within the droplet.
4. The method of claim 1 wherein altering at least one of the magnetic fields further comprises activating an electromagnet proximate only one of the top and bottom surfaces.
5. The method of claim 1 further comprising selectively activating at least one of a plurality of electromagnets positioned proximate the top surface.
6. The method of claim 1 further comprising selectively deactivating at least one of a plurality of electromagnets positioned proximate the top surface.
7. The method of claim 1 further comprising selectively activating at least one of a plurality of electromagnets positioned proximate the bottom surface.
8. The method of claim 1 further comprising selectively deactivating at least one of a plurality of electromagnets positioned proximate the bottom surface.
9. The method of claim 1 wherein altering at least one of the magnetic fields further comprises physically altering a position of a magnet emanating the at least one magnetic field.