Using wettability and interfacial tension to handle droplets of magnetic beads in a micro-chemical-analysis system

We developed a beads-droplet-handling mechanism for micro-chemical-analysis systems that enables us to manipulate magnetic-bead droplets reliably. Differences in wettability and the interfacial tension between different liquids prevent the beads from sticking to the glass surfaces. We also developed mechanisms for extracting and fusing bead droplets and confirmed that beads can be effectively condensed and rinsed by combining extraction and fusion units. The average liquid volume of an extracted droplet containing a bead cluster was 30 nl, which is almost the same of that of the void space in a closely packed bead-cluster structure. An extracted droplet can be diluted 1600-fold with our droplet extraction and fusion process by using a fresh droplet. The primary advantage of the system is that it does not need mechanical devices such as pumps, valves, and filters for handling a solution.