Electrolyte Potential Control Schemes for Redox‐Cycling

Redox‐cycling at interdigitated microelectrode arrays provides amplified current signals for the detection of electroactive species. However, stable operation conventionally requires a reference electrode to control the electrolyte potential. Here, a two‐dimensional finite‐element model based on Nernst–Planck transport and Butler–Volmer electrode kinetics was developed to analyze the influence of electrolyte potential on redox‐cycling currents. The model was parameterized for the p‐aminophenol/quinoneimine redox couple and reproduced experimentally reported steady‐state currents of approximately 80 nA for 10 µM p‐aminophenol. For the investigated sensor system, the simulations show a broad current maximum around the optimum electrolyte potential. With generator and collector potentials of +150 and −150 mV, respectively, electrolyte‐potential deviations of ±50 mV had little influence on the redox‐cycling current, whereas deviations of ±100 mV reduced the current by approximately 7.5%. These findings explain the experimentally observed tolerance of the system toward potential drift when Au pseudo‐reference electrodes are used. A reference‐electrode‐free control approach based on maximum‐current‐point detection is proposed. By modulating the electrolyte potential and using the phase‐sensitive current response as an error signal, the counter‐electrode potential is adjusted to maintain maximum redox‐cycling current. SPICE simulations based on FEM‐derived current–potential characteristics demonstrate suppression of drift‐induced current variations. The concept is suitable for compact and highly integrated redox‐cycling sensor systems.