Continuous separation of non-magnetic particles through negative magnetophoresis inside ferrofluids

We present a simple, low-cost, effective, and label-free continuous flow non-magnetic microparticle separation scheme in a microfluidic device under static magnetic fields. The separation process is based on negative magnetophoresis and uses water-based ferrofluids. We exploit the difference in particle sizes to achieve continuous binary separation of fluorescent microparticles with high throughput and efficiency. We demonstrate size-based separation (2.1 μm and 9.9 μm; 2.1 μm and 4.8 μm) of microparticles with close to 100% separation efficiency and a minimum of 10 particles/hour throughput. This new approach opens the door for the development of label-free continuous cellular separation in microfluidic devices with high throughput, efficiency, and reliability.