Application of Magnetic Microspheres for Pyrosequencing on a Digital Microfluidic Platform

One of the key advantages to a lab-on-a-chip system based on digital microfluidics is the reconfigurability and reusability of the same chip for different tasks. The ability to manipulate magnetic microspheres in solution on a lab-on-a-chip will expand the variety of tasks that can be performed if the microspheres are used as reagent immobilization surfaces. Because the microspheres can be transported in solution and immobilized by a magnetic field, the use of microspheres on-chip will not alter the reconfigurability or reusability of the chip. The retention of 8 μm diameter magnetic microspheres during droplet splitting has been demonstrated on a digital microfluidic platform. A droplet of deionized water was merged with a droplet containing magnetic microspheres, and Neodymium-Iron-Boron magnets were placed on the cover plate of the electrowetting chip. When the combined droplet was split, the magnetic microspheres were isolated in the daughter droplet in closest proximity to the magnets. Retention rates of microspheres during droplet splitting were observed at and above 88% retention. This result has important implications for the eventual goal of performing a substrate-based process such as pyrosequencing. The ability to retain magnetic microspheres during droplet splitting will allow the microspheres to combine with and split from various reagents as well as to be washed of reaction by-products or excess reagent without removing the microspheres from the chip.