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Electrochemical Characterization and Surface Analysis of Activated Glassy Carbon Neural Electrodes

Glassy carbon (GC) neural electrodes have recently gained visibility thanks to their great resistance to corrosion combined to their ability to record and stimulate neuronal activity. To enhance their electrochemical performance, GC electrodes are often subjected to activation, either through electrical or chemical means. In this study, we have compared the activation of GC electrodes performed using electrical biphasic pulses to chemically-induced activation. Because the GC electrodes used for this research are made by pyrolysing SU-8 photoresist - and thus they undergo massive shrinkage during carbonization - 2 electrode diameters were investigated (300 and 50 µm) with the aim of understanding if their surface composition and their ability to get activated change with their geometry. Chemical activation was induced by immersing the electrodes in 2 solutions: A1 and A2, 30 and 150 mM H2O2/PBS (hydrogen peroxide in phosphate buffered saline) respectively. The comparison between activation methods was done by measuring GC electrodes impedance, charge storage capacity (CSC) and by performing surface analysis, before and after the treatments. Results show that impedance drops in all the cases, especially at low frequencies (< 1 kHz) and that there is always an increase in CSC. Raman spectra and relative intensities of disorder are very similar for both electrode diameters and before and after every treatment. X-Ray photoelectron spectroscopy (XPS) interestingly shows graphite content only on the 300 µm electrodes and a high percentage of graphite only on the pristine one. Apart from oxygen and nitrogen, no other species were present on the electrodes surface. In conclusion, both electrically and chemically-induced activation help improving the electrochemical performance of GC electrodes without harming them.