Droplet actuator devices and methods employing magnetic beads

A method of providing a droplet in contact with magnetically responsive beads and having a reduced quantity of a substance, the method comprising:

• (a) providing a droplet actuator comprising:
• (i) magnet sets and electrode sets, wherein:
• (1) each electrode set comprises one or more electrodes associated with a substrate;
• (2) two or more electrode sets are arranged to form an array of electrodes and configured for conducting one or more droplet operations;
• (3) each magnet set comprises one or more magnets;
• (4) each magnet set is arranged in a relationship with an electrode set such that magnetic field(s) exerted by the magnet set restricts a mobility of the magnetically responsive beads to a locus which is proximate to the electrode set;
• and
• (5) each magnet set is arranged in relationship to an adjacent magnet set(s), which relationship is a polar opposite to a polar orientation of the adjacent magnet set;
• (ii) a starting droplet associated with each electrode set, each starting droplet comprising:
• (1) magnetically responsive beads;
• (2) a starting quantity of the substance;
• and
• (3) a starting volume;
• (b) conducting one or more droplet operations to merge a wash droplet with each starting droplet to yield a combined droplet associated with each electrode set;
• (c) magnetically immobilizing the magnetically responsive beads at a target droplet splitting zone on each electrode set;
• (d) conducting one or more droplet operations comprising droplet dividing operations selected to divide the combined droplet at the droplet splitting zone to yield a set of droplets on each electrode set comprising:
• (i) a droplet comprising substantially all of the magnetically responsive beads and having a decreased quantity of the substance relative to the starting concentration;
• and
• (ii) a droplet substantially lacking the magnetically responsive beads;
• and wherein (d) is conducted without removing the magnet set immobilizing the magnetically responsive beads.