A novel width-expanding spiral microchannel for high-throughput continuous separation of bacterial-sized particles

Separating target particles (e.g., bacteria) from complex media is critical to preventing matrix interference in the detection and analysis of target substances. However, existing techniques still face challenges in improving throughput for the separation of bacteria-sized particles. To address this, we present a novel width-expanding spiral microchannel designed for continuous, high-throughput separation of bacteria-sized particles from larger particles. The separation principle and the effect of width variation on separation performance were assessed through numerical simulations and experimental tests. Numerical results indicate that, compared to a constant-width microchannel, a width-expanding microchannel exhibits a lower Dean flow distribution due to the gradually increasing aspect ratio, resulting in delayed migration of smaller particles due to Dean flow. This migration lag can be compensated by increasing the operating flow rate. Fluorescent microsphere experiments demonstrated that the width-expanding microchannel achieved 99.20% and 96.70% separation efficiencies for 1 μm microspheres from mixtures containing 7 μm and 10 μm microspheres, respectively, at flow rate of 170 µL/min, thereby surpassing the performance of existing technologies. Considering separation performance, pressure drop, and processing throughput, the width-expanding microchannel ensures both high separation efficiency and lower pressure drops, enabling higher-throughput operation. This innovative design holds significant promise for enhancing bacterial isolation from infected blood and reducing the time required for bacterial pretreatment.