Real-Time Monitoring\nof Electrode Surface Changes\nin Fast-Scan Cyclic Voltammetry Using Fourier Transform Electrochemical\nImpedance Spectroscopy

Fast-scan cyclic\nvoltammetry (FSCV) is a widely used\nelectrochemical\ntechnique to measure the phasic response of neurotransmitters in the\nbrain. It has the advantage of reducing tissue damage to the brain\ndue to the use of carbon fiber microelectrodes as well as having a\nhigh temporal resolution (10 Hz) sufficient to monitor neurotransmitter\nrelease in vivo. During the FSCV experiment, the surface of the carbon\nfiber microelectrode is inevitably changed by the fouling effect.\nIn terms of redox peak potential and sensitivity against neurotransmitters,\na changed electrode surface results in a voltammogram that differs\nfrom the precalibration. However, when an electrode is implanted in\nthe brain, the method for monitoring the electrode status change is\nlimited. In this study, we propose employing an electrochemical impedance\nconcept to monitor the gradual change of the electrode surface during\nFSCV scanning. Fourier transform electrochemical impedance spectroscopy\n(FTEIS) was used in combination with FSCV to detect the real-time\nimpedance of the electrode. The relationship between impedance and\nelectrode surface conditions was studied by immersing carbon fiber\nmicroelectrodes in bovine serum albumin solution to induce biofouling\nand diminish electrode sensitivity. As a result of the nonspecific\nadsorption of bovine serum albumin during the interleave scan of FSCV\nand FTEIS, both the measured dopamine response and the capacitance\nof the equivalent circuit model from FTEIS decreased over time. The\ncapacitance and sensitivity of the electrode showed correlation (R<sup>2</sup> = 0.90), while the resistance of the equivalent circuit did\nnot. In vivo measurements using the interleave scan of FSCV and FTEIS\nwere also carried out to observe biofouling on the FSCV electrode\nsurface and to measure dopamine sensitivity in the striatum of the\nrat brain for an hour. The results showed that the resistance did\nnot significantly change, while capacitance and measured dopamine\nwere significantly diminishing over time. In summary, real-time neurotransmitter\nmeasurements and electrode monitoring with the combination of FSCV\nand FTEIS would be useful in neuroscience research.