Spiral microchannel with stair-like cross section for size-based particle separation

Particle separation has a variety of applications in biology, chemistry and industry. Among them, circulating tumor cells (CTCs) separation has drawn significant attention to itself due to its high impact on both cancer diagnosis and therapeutics. In recent years, there has been growing interest in using inertial microfluidics to separate micro/nano particles based on their sizes. This technique offers label-free, high-throughput and efficient separation and can be easily fabricated. However, further improvements are needed for potential clinical applications. In this study, a novel inertial separation technique using spiral microchannel having stair-like cross section is introduced. The design fundamental concepts, design criteria and efficacy are investigated thoroughly using a robust numerical model; moreover, it is experimentally tested on the fabricated spiral microchannel. Based on the results, in contrast to conventional spiral microchannels, in which the flow vortices are located latitudinal, the two vortices are uniquely placed longitudinally in the stair-like cross section. The numerical and experimental results indicate that there is a size-dependent volume flow rate threshold defined for each particle size determining which vortices become equilibrated and consequently facilitate their separation. According to the results, using stair-like cross section, the separation throughput and resolution, as the two important design criteria in CTCs’ separation techniques, are significantly improved compared to the conventional spiral microchannels.