Digital microfluidics chip with integrated intra-droplet magnetic bead manipulation

This paper demonstrates an integrated device combining both EWD droplet actuation and intra-droplet magnetic bead manipulation. Magnetic bead manipulation is achieved by using current-carrying wires acting as microelectromagnets. The current wire structure is capable of segregating and separating magnetic beads within a droplet. By adjusting the amount of current in the wire structure, high segregation efficiency within the droplet is shown and the separation of two kinds of beads is realized within a distance of 65 A mu m. The EWD droplet actuation function and the magnetic bead separation function can be operated independently, which provides flexibility when designing operation protocols. The current wire structure is embedded in an EWD electrode without affecting droplet actuation. The vertical structure of the device and its fabrication process are also the same as a normal EWD device. Magnetic bead segregation efficiency of 96.8 % was achieved for 2.8-A mu m beads that were collected over a distance of 65 A mu m during a 20-s current pulse. Droplet splitting is shown to allow complete separation of beads into one of the two daughter droplets. And, intra-droplet separation of 1- and 2.8-A mu m beads was demonstrated over an average distance of 65 A mu m. This experiment shows the feasibility of performing separation in droplets with a complex mixture of multiple beads, each having different magnetic contents.