The relevance of the initial conditions in glassy carbon electrode sensing applications: the ferri/ferrocyanide redox reaction model system in aqueous solution

Abstract

Carbon electrodes, especially the glassy carbon electrodes (GCE) are widely accepted as very versatile sensing platforms. However, correlating the behaviour of the ferri/ferrocyanide redox couple ([Fe(CN)6]3-/4−) with the GCE's surface modification is challenging. The surface modification can be achieved by applying a pre-conditioning electrochemical activation procedure. Hence, we report the investigation performed in order to provide further insights into the electrochemical behaviour of the commonly used redox probe in aqueous solutions. To that aim we took advantage of powerful and complementary electrochemical analytical techniques, like cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Thus, this work highlights the critical role of the GCE initial conditions for optimizing the charge transfer processes and therefore to improve the [Fe(CN)6]3-/4− performance in sensing applications. The best results were obtained in phosphate buffer saline solution with previous electrochemical activation by fast potential cycling between [-0.5 and +1.8] V (vs. Ag|AgCl (KCl sat.)). Finally, one can consider this an eco-friendly and simple procedure to be carried out in the lab, however, its use must be carefully optimized when exploring other systems, as highlighted herein.