Comparative Studies of Graphitic material Interaction with Flame Retardant 4 (FR-4) Substrate for Miniature Electrochemical-based pH Sensor

In this paper, we present studies of graphitic materials clad on a working electrode (WE) for a miniaturised three-electrode electrochemical-based pH sensor. The sensor was fabricated on a flame retardant 4 (FR-4)-based printed circuit board (PCB), with additional layers of electroplated nickel (Ni) and gold (Au) to shield the base copper cladding from corrosion. In this study, Au, graphene oxide (GO)/polyvinyl alcohol (PVA), and reduced graphene oxide (rGO)/PVA were used for fabricating WEs, then each electrode was analysed for its capability to produce a reversible redox reaction. Cyclic voltammetry (CV) measurements showed that all the fabricated WEs can produce a reversible redox reaction, with different peak currents. This showed that the functional groups within GO plays an important role in the pH sensing mechanism with their open-circuit potential varying with different pHs. The optimised fabricated WEs were integrated with reference and counter electrodes, then characterised for pH sensor application. Among all the sensors, GO/PVA showed the highest sensing capability of 8.3 mV/pH.