Microfluidic continuous particle/cell separation via electroosmotic-flow-tuned hydrodynamic spreading

Among the microfluidic separation methods, hydrodynamic spreading is a simple and high-throughput continuous separation technique based on the difference in size. However, it is difficult to adjust tiny pressure differences accurately in microfluidic devices. In this study, a combination of electroosmotic flow (EOF) and hydrodynamic flow spreading was employed to tune the size separation of particles. A stream with different kinds of particle suspensions was driven co-fluently with a particle-free carrier stream under both mechanical external and electroosmotic pressure in a microchannel. The EOF-tuned hydrodynamic spreading behaviour was investigated experimentally and modelled through an electric equivalent model and numerical simulation. When the magnitudes of the mechanically and electroosmotically induced pressures were similar, the EOF tuning on the pressure-driven flow became significant. Hence, the hydrodynamic spreading could be easily adjusted by a tuned power supply. The separation was studied in more detail with 1.9 and 9.9 µm fluorescent polystyrene particles. Moreover, separation of E. coli and yeast cells was accomplished. In conclusion, this technique has the advantages of good stability of mechanical-pressure-driven flow and precise tuning of the EOF, and provides a robust method for size-based separation of particles and cells.