Impedance Spectroscopy Unveils Interfacial Dynamics in NiO-Modified Electrodes for Glucose Detection

Electrochemical impedance spectroscopy (EIS) is a powerful tool for probing the interfacial properties and reaction mechanisms of electrochemical sensors. In this study, we extensively utilized EIS to analyze the interaction between nickel oxide (NiO) polyhedra and glucose at the electrode interface, providing deep insights into the performance of nonenzymatic glucose sensors. NiO polyhedra were synthesized via the direct thermal decomposition of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), a scalable and straightforward method that remains underutilized in electrochemical sensing applications. The synthesized NiO was used to modify glassy carbon electrode (GCE) and screen-printed electrodes (SPE). The electrochemical glucose-sensing properties of these NiO-modified electrodes were assessed using cyclic voltammetry (CV) and chronoamperometry (CA), with EIS playing a crucial role in elucidating the electrode interface interactions. The NiO/GCE demonstrated high sensitivity for glucose detection, achieving 1109 μA mM–1 cm–2 in the glucose concentration range of 5 μM to 1 mM and 737.7 μA mM–1 cm–1 from 1 mM to 6 mM, with a detection limit of 1.1 μM. Notably, the sensitivity decreased at higher glucose concentrations, indicating two distinct linear ranges. EIS measurements were conducted at varying potentials for two constant glucose concentrations to investigate this phenomenon. The EIS analysis revealed a flip in the impedance spectra or negative resistance at higher glucose concentrations, providing detailed information about charge transfer resistance and interfacial kinetics, which explained the observed changes in sensitivities in CV and CA experiments. The electrode exhibited excellent selectivity over common interferents, along with reproducible and stable performance. The extensive use of EIS not only provided a deeper understanding of the electrode processes but also highlighted the effectiveness of the thermally decomposed NiO polyhedra in enhancing sensor performance. This work underscores the potential of NiO-modified electrodes for nonenzymatic glucose sensing and demonstrates the critical role of EIS in advancing electrochemical sensing technologies.