Sheathless and high throughput sorting of paramagnetic microparticles in a magneto-hydrodynamic microfluidic device.

Sorting of microorganisms and particles from a mixture is critical for numerous biotechnological and medical applications. Several sorting methods such as pinched flow fractionation (PFF), optical sorting, dielectrophoresis, acoustic separation, magnetophoresis and deterministic lateral displacement (DLD) have been reported in literature. But most of these methods lack ideal characteristics of a sorter such as ability to process at high throughput, simple design, non-complicated fabrication method, sheathless operation and high purity in separation. In this paper, we have introduced a novel sorting technique by integrating focusing of magnetic particles in a narrow microchannel with their hydrodynamic separation at a downstream expansion channel which meets majority of the aforementioned characteristics. To achieve this, the sheathless focusing of paramagnetic microparticles in the narrow microchannel and their deflection at the expansion channel were first studied at various flow rates (0.5-5 ml h-1). Then, a mixture of 5 and 11 μm paramagnetic particles was introduced into the device and their separation was examined quantitatively. It was found that the magnetic particles were focused along the wall of channel, however their centers were positioned on two distinct streamlines owing to difference in their sizes. Hence, these two particles were found separated from each other as they flew into the expansion region. This technique of size based separation of paramagnetic particles works at a high throughput of 107 particles per hour and offers more than 98% purity in sorting.