Revisiting Background Signals and the Electrochemical Windows of Au, Pt, and GC Electrodes in Biological Buffers

For electrochemical experiments involving biological buffers, pH values, ions, and electrode materials play major roles in the electrochemical readout of the measurements. When conducting electrochemical experiments, background signals are sometimes mixed with true signals, easily leading to a wrong interpretation of the data. These background signals are easily induced by the reactions between buffers and electrode materials. However, these background signals have rarely been studied systematically. In response to rapid developments in the field and application of bioelectrodes, we conducted a much-needed systematic study of these background signals and the electrochemical windows in buffers-specifically, of the electrochemical windows gold, glassy carbon, and platinum in three most commonly used biological buffers, namely, Tris, HEPES, and phosphate. We examined the pH effect using HCl, H2SO4, and NaOH to modulate the pH values from 6.0 to 9.0 in the three buffers. Furthermore, through comparison of HCl and H2SO4, we were able to illustrate the reaction between Cl- ions and the metallic electrode. This reaction also led to clear redox peaks as background signals in cyclic voltammograms. When a high potential was applied, the formation of hydroxide was evident on the metallic electrode, which led to a clear reduction peak in cyclic voltammograms. In addition, we used an atomic force microscope to monitor the morphology of the electrode surface when a cyclic potential was applied. All tests were conducted in the presence of 100 mM LiClO4 which was used as the electrolytes. These characterization results yield critical insights into electrode surface reactions, insights which are crucial for precisely interpreting electrochemical results measured in biological buffers. This fundamental study provides comprehensive information, which is especially helpful for the development of bioelectrode materials and bioelectronics applications.