Effective dean vortex separation at reduced flow rates towards rare cell sorting.

The study focuses on the design of a spiral microfluidic device, aiming to efficiently sort particle by size, at tailored flow rate for downstream processing. While spiral devices exploiting Dean vortices are recognized for their high-throughput capabilities, they often require high flow rates that limit their integration with other microfluidic functions and reduce sorting performance. Our work aims to design a low flowrate-operating-spiral (~ 50 mL/h) by investigating the influence of spiral geometric parameters and flow conditions on sorting efficiency. Through combined experimental and theoretical analysis, we evaluate how particle size and flow dynamics determine particle positions within the spiral, validating underlying models. This approach provides valuable insights for optimizing spiral microfluidic systems particularly their design, performance, and versatility in applications such as the isolation of rare cell isolation. The spiral design achieved efficient size-based sorting of 10 and 15 μm microbeads at a flow rate of 50 mL/h. When applied to biological samples, the system removed 89% of white blood cells from a 1:1 lysed blood sample (≈ 10⁷ cells/min) while maintaining a recovery of more than 75% for all tested CTC-mimicking cells.