Continuous-Flow Electrokinetic-Assisted Plasmapheresis by Using Three-Dimensional Microelectrodes Featuring Sidewall Undercuts.

We present a novel plasmapheresis device designed for a fully integrated point-of-care blood analysis microsystem. In the device, fluidic microchannels exhibit a characteristic cross-sectional profile arising from distinct three-dimensional (3D) microelectrodes featuring sidewall undercuts readily integrated through a single-mask process. The structure leverages mainly electrothermal convective rolls that efficiently manifest themselves in physiological fluids and yet have received inadequate attention for the application of plasmapheresis due to concerns over Joule heating. Using this device, we show that such convective rolls not only lead to plasma extraction at a high yield and purity but also deliver plasma at an acceptable quality with no evidence of hemolytic stress or protein denaturation. Specifically, plasma from 1.5 μL of whole blood diluted to 4% hematocrit in a high-conductivity buffer (1.5 S/m) is extracted in a continuous flow at a fraction of 70% by using a peak voltage of ±10 Vp applied at 650 kHz; the extracted plasma is nearly 99% pure, as shown by a rigorous assessment using flow cytometry. The plasmas obtained using this device and using conventional centrifugation and sedimentation are of comparable quality as revealed by absorbance and circular dichroism spectra despite thermal gradients; however, these gradients effectively drive electrothermal bulk flows, as assessed using the microparticle image velocity technique. The device achieves high target molecule recovery efficiency, delivering about 97% of the proteins detected in the plasma obtained using sedimentation. The utility of the extracted plasma is further validated based on the detection of prostate-specific antigen at clinically relevant levels.