Contact Activation in Dielectric Blood Coagulometry: A Comparison of Screen-Printed and Sputtered Gold Electrodes of ClotChip Microfluidic Sensor

This letter investigates the effect of surface roughness on the kinetics of whole blood coagulation through a comparative study of two different electrode fabrication techniques, i.e., screen printing and sputtering, for a microfluidic dielectric sensor termed ClotChip. Featuring a 3D parallel-plate capacitive sensing structure with gold sensing and floating electrodes deposited on polymethyl methacrylate plastic substrates, we have previously shown that ClotChip can measure the temporal variation in the normalized real permittivity of a coagulating whole blood sample (<10 µL) at 1 MHz and provide clinically useful information on the coagulation time of the sample through a time-to-permittivity peak (
T
_peak
) readout parameter. In this letter, scanning electron microscope imaging and profilometry measurements reveal that the surface of the sputtered gold electrode is much smoother than the rough surface of its screen-printed counterpart, having a mean arithmetic average height and root-mean-square roughness of ∼38.0 and 47.0 nm versus 5.7 and 7.2 µm for the screen-printed electrode. The ClotChip
T
_peak
parameter has also been measured for both untreated whole blood samples and those modified
in vitro
with corn trypsin inhibitor: an inhibitor of the activated coagulation factor XII (FXIIa) used to suppress surface-induced coagulation by contact activation. Our results establish that surface-induced FXIIa-mediated contact activation plays a more prominent role in accelerating the kinetics of whole blood coagulation for rough screen-printed electrodes than for smooth sputtered electrodes.