Patent ID: 8637317

Claim:
A method of washing beads comprising: (a) providing a droplet actuator comprising: (i) two substrates arranged to provide a gap; (ii) electrodes associated with one or both of the two substrates and arranged for conducting droplet operations in the gap; (iii) a starting droplet situated in the gap comprising magnetically responsive beads within a region of a magnetic field and a starting concentration of the substance; (b) conducting one or more electrowetting-mediated droplet operations to merge a wash droplet with the droplet provided in step (a)(iii) to yield a combined droplet; (c) conducting one or more droplet operations while restraining the beads to divide the combined droplet, yielding a set of daughter droplets comprising: (i) a first daughter droplet retaining at least about 99% of the beads and having a decreased concentration of the substance relative to the starting concentration; (ii) a second daughter droplet which is separated from the at least one surface; and (d) transporting the first daughter droplet away from the magnetic field.