Magnetic separation of particles and cells in ferrofluid flow through a straight microchannel using two offset magnets

The separation of particles and cells is critical in many chemical and biological applications. This work presents a simple idea for utilizing a pair of permanent magnets to continuously separate diamagnetic particles and cells in ferrofluid flow through a straight microchannel. The first magnet is placed close to the microchannel for focusing the particle mixture to a single stream without the use of a sheath flow. The second magnet, which is offset from the first magnet and placed farther from the channel, is to displace the aligned particles to dissimilar flow paths for a continuous sorting. This idea is first demonstrated through the separation of 3μm- and 10μm-diameter polystyrene particles, where the effects of flow speed and magnet distance are both examined. The experimental data are found to fit well with the predictions of an analytical model. Furthermore, a continuous separation of live yeast cells from 10μm polystyrene particles is implemented in the same device. •We develop a simple diamagnetic particle and cell separation technique in ferrofluids.•Two offset magnets are used to achieve a sheath-free continuous separation in a straight microchannel.•The technique is demonstrated through the magnetic separation of polystyrene particles and yeast cells.•The effects of ferrofluid speed and magnet-channel distance are examined on particle separation.•The predictions from an analytical model agree with the experimental data quantitatively.