Label-Free, Sheathless Ferrohydrodynamic Microfluidic Chip for Size-Dependent Sorting

To address the issue of sample dilution associated with sheath flow dependency in conventional microfluidic sorting systems, a sheathless sorting chip leveraging ferrohydrodynamic effects was developed. By integrating Dean flow pre-focusing in asymmetric serpentine channels with gradient magnetic field modulation, precise separation of size-similar particles was achieved without the need for sheath flow. Halbach magnet arrays were implemented to maintain effective magnetic gradients up to 0.5 mm from the channel, overcoming the challenge of constructing magnetic fields over short distances. Experimental results demonstrated a size resolution of 5 m at a throughput of 6×104 particles/min, with sorting purity reaching 82.6% and 82.2% for 20 m and 15 m microspheres, respectively. This technology provides a novel approach for label-free, sheathless sorting of rare biological particles, such as circulating tumor cells, with significant scientific and practical implications.