Microfluidic device for continuous blood plasma separation from whole blood

Sample preparation is a critical step in clinical diagnostics, as plasma must be separated from whole blood before analysis. Conventional centrifugation is time-consuming, require bulky equipment, and is unsuitable for point-of-care (POC) applications. Here, we present a simple and low-cost microfluidic device that achieves continuous (uninterrupted flow separation without batch processing) and real-time (immediate flow separation and inline without delays) plasma separation from undiluted whole human blood without external forces. Six channel geometries were evaluated by numerical simulations to investigate the effects of side-channel orientation and channel height on red blood cell (RBC) contamination carryover. The optimized configuration with a 20-μm channel height, minimized recirculation zones and enhanced inertial focusing, leading to reduced RBC contamination in the side channel plasma outlet. Devices were then fabricated by standard photolithography and soft lithography. Experimental validation with whole human blood demonstrated that the device significantly reduced red blood cell (RBC) contamination across a flow rate range of 0.05-0.2 mL min^-1, yielding plasma with substantially lower RBC levels compared with whole blood, although low residual RBCs were still present. Flow cytometry further confirmed an efficient depletion of peripheral blood mononuclear cells (PBMCs), resulting in markedly lower leukocyte content than in plasma obtained by standard centrifugation. The plasma yield reached 3.8 %, corresponding to an extraction rate of 6.5 μL min^-1, and hemolysis levels remained comparable to centrifuged samples, indicating preservation of plasma integrity. This established device provides a robust platform for high-purity plasma separation and has a strong potential for point-of-care diagnostic applications.