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.