An improved electrochemical biosensing device architecture with ultra-thin and surface-modified dielectric stacking structure

Abstract

Electrochemical capacitive sensors typically employ a planar electrode (PE) design on a dielectric substrate to evaluate target-induced changes in electrical double-layer (EDL) capacitance. However, as functional substrate areas shrink down to the nanoscale, sensor performance becomes highly sensitive to subtle variations in electrode shape and spacing. These present significant challenges for mass production. To address these issues, we introduce microwell array (MWA) capacitive sensors, which replace the conventional planar layout with a vertically stacked electrode design. This architecture preserves the benefits of nanoscale PE sensors while shifting the fabrication complexity of the sensing area from nanolithography to a more scalable chemical vapor deposition (CVD) process. To evaluate the performance compared to conventional PE-based sensors, we demonstrate biosensing application with the proposed MWA capacitive sensors. In brief, we develop a fabrication process that achieves ultra-thin dielectric layers of 240 nm and 60 nm between MWA electrodes, with fabrication reliability rates of 89.29 % and 50.71 %, respectively. Moreover, simulations reveal that the asymmetric electrode geometry of MWA sensors enhances near-surface current compared to PE sensors. We experimentally show that this effect becomes more pronounced as the dielectric layer thickness decreases. Finally, we also demonstrate that the lateral substrate of MWA sensors supports stable functionalization with an AEAPTES-biotin layer, as confirmed by surface potential measurements. Leveraging these technical advancements, the MWA sensor achieves Avidin and Streptavidin detection limit as 120 fM and 1.76 pM, respectively. These results underscore the potential of the proposed MWA capacitive sensors, demonstrating their superiority over conventional PE sensors for advanced biosensing applications.