Rapid and continuous magnetic separation in droplet microfluidic devices

This paper presents a droplet microfluidic method to extract molecules of interest from a droplet in a rapid and continuous fashion. We accomplish this by first marginalizing functionalized superparamagnetic beads in within the droplet using a magnetic field, and then splitting the droplet into one droplet containing the majority of magnetic beads and one droplet containing the minority fraction. A similar enrichment strategy have been reported in the recent literature [1, 2] using a 50:50 tshaped splitting junction but a quantitative analysis and optimization of the factors that affect the enrichment efficiency was lacking. In contrast, we quantitatively analyzed the factors that affect the efficiency of marginalization and droplet splitting. We also improved the design of the splitting junction to allow the preferential extraction of bead-rich regions of the droplets resulting in a 5x enrichment of magnetic beads during a single pass.