Real-Time Monitoring of Electrode Surface Changes in Fast-Scan Cyclic Voltammetry Using Fourier Transform Electrochemical Impedance Spectroscopy

Fast-scan cyclic voltammetry (FSCV) is a widely used electrochemical technique to measure the phasic response of neurotransmitters in the brain. It has the advantage of reducing tissue damage to the brain due to the use of carbon fiber microelectrodes as well as having a high temporal resolution (10 Hz) sufficient to monitor neurotransmitter release in vivo. During the FSCV experiment, the surface of the carbon fiber microelectrode is inevitably changed by the fouling effect. In terms of redox peak potential and sensitivity against neurotransmitters, a changed electrode surface results in a voltammogram that differs from the precalibration. However, when an electrode is implanted in the brain, the method for monitoring the electrode status change is limited. In this study, we propose employing an electrochemical impedance concept to monitor the gradual change of the electrode surface during FSCV scanning. Fourier transform electrochemical impedance spectroscopy (FTEIS) was used in combination with FSCV to detect the real-time impedance of the electrode. The relationship between impedance and electrode surface conditions was studied by immersing carbon fiber microelectrodes in bovine serum albumin solution to induce biofouling and diminish electrode sensitivity. As a result of the nonspecific adsorption of bovine serum albumin during the interleave scan of FSCV and FTEIS, both the measured dopamine response and the capacitance of the equivalent circuit model from FTEIS decreased over time. The capacitance and sensitivity of the electrode showed correlation (R² = 0.90), while the resistance of the equivalent circuit did not. In vivo measurements using the interleave scan of FSCV and FTEIS were also carried out to observe biofouling on the FSCV electrode surface and to measure dopamine sensitivity in the striatum of the rat brain for an hour. The results showed that the resistance did not significantly change, while capacitance and measured dopamine were significantly diminishing over time. In summary, real-time neurotransmitter measurements and electrode monitoring with the combination of FSCV and FTEIS would be useful in neuroscience research.