Magneto-Hydrodynamic Fractionation (MHF) for continuous and sheathless sorting of high-concentration paramagnetic...

Sorting cells, microorganisms and particles from a solution is of paramount importance in many biological applications. An ideal sorting device should work at high throughput, involve simple design, avoid energy consumption, operate without a diluting sheath flow and perform separation with high purity. However, currently available sorting methods such as pinched flow fractionation, hydrodynamic filtration, magnetophoresis and deterministic lateral displacement meet only a few of the above-mentioned characteristics. In this paper, we report a hybrid technique combining magnetic focusing of particles in a thin microchannel and their hydrodynamic fractionation at a downstream expansion region, to devise a sheathless and high-throughput Magneto-Hydrodynamic Fractionation (MHF) method. First, sheathless magnetic focusing of 11 μm microparticles against the wall of the thin microchannel was investigated over a wide range of flow rates (0.5-5 mL h^-1). Then, a mixture of 5 μm and 11 μm paramagnetic particles was injected into the device at a flow rate of 5 mL h^-1 to demonstrate their sorting. Both of these magnetic particles were aligned along the wall of the channel and hence focused in the device, however their centers were lying on different streamlines due to their different sizes. Therefore, they were separated into distinct streamlines upon entering into the expansion region. Using this device, we achieved a high throughput sorting of more than 10⁴ particles per second with an approximate on-chip fractionation purity of 98%. This technique has a great potential for separation of more than two magnetic particles for application in immunomagnetic affinity-based sorting of multiple biological substances.