Towards a reliable and high sensitivity O₂-independent glucose sensor based on Ir oxide nanoparticles

The primary goal of this work is the development of a rapidly responding, sensitive, and biocompatible Ir oxide (IrOx)-based glucose sensor that regenerates solely via IrOx-mediation in both O₂-free and aerobic environments. An important discovery is that, for films composed of IrOx nanoparticles, Nafion® and glucose oxidase (GOx), a Michaelis-Menten constant (K'(m)) of 20-30 mM is obtained in the case of dual-regeneration (O₂ and IrOx), while K'(m) values are much smaller (3-5 mM) when re-oxidation of GOx occurs only through IrOx-mediation. These smaller K'(m) values indicate that the regeneration of GOx via direct electron transfer to the IrOx nanoparticles is more rapid than to O₂. Small K'(m) values, which are obtained more commonly when Nafion® is not present in the films, are also important for the accurate measurement of low glucose concentrations under hypoglycemic conditions. In this work, the sensing film was also optimized for miniaturization. Depending on the IrOx and GOx surface loadings and the use of sonication before film deposition, the i(max) values ranged from 5 to 225 μA cm⁻², showing very good sensitivity down to 0.4 mM glucose.