Bioactive Hydrogel Layers on Microdisk Electrode Arrays: Impedimetric Characterization and Equivalent Circuit Modeling

Microfabricated microdisk electrode arrays (MDEAs) of 50 μm (5184 disks), 100 μm (1296 disks) and 250 μm (207 disks) ( d / r =4; A= 0.1 cm 2 ) were coated with poly(hydroxyethylmethacrylate)‐based hydrogel membranes and studied by electrochemical impedance spectroscopy (EIS) in 1.0 mM ferrocene monocarboxylic acid (FcCO 2 H). Equivalent circuit modeling showed an approximate three‐fold increase in solution resistance, R sol , and an order of magnitude increase in charge transfer resistance, R ct, resulting from a reduction in apparent diffusivity of FcCO 2 H. Additionally, both resistive parameters decreased while the capacitance ( Q ) increased with decreasing microdisk diameter; consistent with an increase in effective electroactive area. The hydrogel layer did not compromise enhanced mass transport achieved by the MDEA and thus may be used to advantage in biosensors.