Electrode–Electrolyte Interface Impedance Characterization of Ultra-Miniaturized Microelectrode Arrays Over Materials and Geometries for Sub-Cellular and Cellular Sensing and Stimulation

Electrochemical interfaces with low-impedance, high biocompatibility, and long-term stability are of paramount importance for microelectrode arrays (MEAs), that are widely used in numerous cellular sensing/stimulation applications, e.g., brain interface, electroceuticals, neuroprosthetics, drug discovery, chemical screening, and fundamental biological research. It is becoming increasingly critical since sensing/actuations at sub-cellular resolution necessitate ultra-miniaturized electrodes, which exhibit exacerbated electrochemical interfaces, especially on interfacial impedance. This paper reports the first comprehensive characterization and interfacial electrochemical impedance spectroscopy (EIS) of the ultra-miniaturized electrodes for different electrode sizes (8×8 μm², 16×16 μm², and 32×32 μm²) and a wide material collection (Au, Pt, TiN, and ITO). Equivalent electrochemical interfacial circuit models with interface capacitance, charge transfer resistance, and solution resistance are obtained for all the electrode designs based on their EIS measurements. The results can potentially guide the designs of ultraminiaturized MEAs for future bioelectronics systems.