Development of a Novel Three-Dimensional Parallel-Plate Biochemical Sensor for Electrochemical Impedance Spectroscopy (EIS)

Miniaturized electrochemical impedance-based biochemical sensors have been extensively used for detection of chemical and biological agents at extremely low concentrations. The majority of the sensors presented in the literature have a two-dimensional (planar) geometry and use two interdigitated electrodes that are exposed to an aqueous solution for deteciotn. In this work, a novel three-dimensional sensor is presented that uses a parallel-plate geometry for sensor structure. The sensor has a digitated electrode patterned on the substrate and a planar and porous electrode suspended above the fixed electrode. The sensor is fabricated using PolyMUMPs and diethylhexyl phthalate (DEHP) is used to demonstrate the ability of the sensor for biochemical detection. The measurement results show that the sensor has distinct Nyquist responses for 0.02 ppm, 0.2 ppm, 2 ppm and 10 ppm concentrations of the DEHP. Different electrochemical phenomena such as double-layer capacitance formation and charge transport at high frequencies, and diffusion at low frequencies are detected using Nyquist plots. The experimental results show that, for 3D parallel-plate sensors, in contrast to interdigitated geometry, the electrostatic effect is noticeable, and the parallel-plate capacitance due to the dielectric effect of the solution notably affects the Nyquist response. This is an important effect, specially for biological detection.