High accuracy size-based droplet separation with pinched flow fractionation

Abstract Droplet microfluidics is widely used in biochemical analysis and cell sorting. Conventional droplet-based cell sorting methods typically involve manipulating droplets containing target cells using electric fields or dielectrophoretic forces, which require additional control systems and high voltage. In this study, we investigate the passive structure of pinched flow fractionation to achieve highly accurate separation of droplets with different sizes. The small variation in the sizes of the separated droplets can lead to a reduction in the accuracy of the droplet separation. In our research, we investigate droplet separation through both experiments and simulations, aiming to summarize the principles behind pinched flow separation of droplets. In our experiments, we have successfully separated droplets with diameters smaller than 100 μ m as well as those larger than 110 μ m. Furthermore, we also take into consideration the impact of sheath flow in the separation process. It is important to note that only an adequate sheath flow rate can ensure that the droplets flow smoothly without interference, maintaining a stable trajectory and thereby ensuring accuracy. The findings of this study can serve as a valuable guide for designing passive droplet separation methods for various types of droplet-based cell sorting systems.