Passive Magnetic Separator Integrated with Microfluidic Mixer: Demonstration of Enhanced Capture Efficiency

In this paper, we present two results: (1) a new method for quantifying the efficiency of magnetic bead separators by magnetic measurements, and (2) a new idea for designing efficient magnetic bead separators. For microfluidic magnetic separators, a limiting factor for the capture of magnetic beads is the steep decrease of the magnetic force on the beads as a function of their distance to the magnetic structures. Our idea is to integrate the magnetic separator with a microfluidic mixer to ensure that all beads are brought close to the magnetic structures. We have fabricated a magnetic separator consisting of permalloy elements adjacent to a microfluidic channel. The performance of a system with an integrated surface structured (staggered herringbone) microfluidic mixer is compared to that of an equivalent system without the mixer. It is quantitatively demonstrated that the mixer significantly enhances the bead capture-and-release efficiency.