Tracking Carbon Microelectrode Impedance during Fast-Scan Cyclic Voltammetry

Fast-scan cyclic voltammetry (FSCV) is a powerful technique for monitoring rapid neurochemical fluctuations in living animals. When paired with permanently implanted carbon-fiber microelectrodes, changes in neurochemical dynamics can be monitored over months and related to changes in behavior. However, the performance and electrical properties of handmade microelectrodes are variable and impacted by the biological response to implantation and the physical and chemical diversity of recording environments. These factors collectively impact calibration factors and the shape of the cyclic voltammograms (CVs) that are used for analyte quantification and identification. We previously reported that model RC circuits of variable impedance could be utilized to mimic the observed shifts in FSCV performance that develop in vivo. In this work, an electrochemical impedance spectroscopy (EIS) measurement was incorporated within each voltammetric sweep to provide information on rapid changes in impedance, reactance, and capacitance that impact the electrochemical system during the FSCV experiment. The data, which were collected using standard FSCV equipment, quantify large shifts in these parameters upon implantation in tissue. These shifts were largely mitigated by electrochemical conditioning, as reflected in the voltammetric data. This paired FSCV:EIS paradigm can be used to inform users regarding changes in electrochemical performance that occur at any point during an in vivo experiment, representing a significant step toward in situ calibration strategies and improved accuracy in data analysis.