Rapid-manufacturing and cost-effective single-layer microfluidic device for high-throughput three-dimensional hydrodynamic focusing

Microfluidic devices play a crucial role in the widespread application of single-cell analysis, where hydrodynamic focusing stands out due to its simplicity in structure and excellent adaptability to a wide range of flow rates. Owing to the extensive application of soft lithography, polydimethylsiloxane (PDMS) is widely used in the fabrication of microfluidic devices. However, challenges arise under high-throughput conditions, where the elastic deformation of PDMS can cause microchannel expansion, diminishing focusing effect. To address this challenge, this work introduces a three-dimensional (3D) hydrodynamic focusing device with simplified single-layer structure, which is fabricated by the double transfer process, specifically designed for fabricating polyurethane acrylate (PUA) microfluidic devices. Notably, this approach eliminates the time-consuming heating procedures, which significantly enhances manufacturing speed by an order of magnitude compared to the soft lithography process. To evaluate the practical focusing performance of the microfluidic device, optical time-stretch (OTS) microscopy is employed for high-throughput imaging of clinical urine samples. Experimental results demonstrate that as the flow rate increases, the focusing efficiency gradually improves in both vertical and lateral directions. At an averaged velocity of 16.7 m/s, the focusing efficiency reaches 98.4% in the vertical direction and 95.0% in the lateral direction. Thus, the amalgamation of simplicity, efficiency, and adaptability positions this technology as a promising tool in the realm of microfluidics, particularly for applications requiring precise cell focusing in high-throughput scenarios.