Facile Biosynthesis of Spinel NiCo₂O₄ Nanoparticles for Electrochemical Sensor Development: Highly Sensitive and Selective Detection of Metol in Environmental Samples

Abstract

The development of eco-friendly electrochemical sensors for monitoring toxic phenolic contaminants like metol (4-methylaminophenol sulfate) is critical for environmental and industrial safety. Here, we report a novel biosynthesized spinel NiCo₂O₄ nanoparticlesmodified carbon paste electrode (NiCo₂O₄ NPs/CPE) for the ultrasensitive, selective, and low-cost detection of metol in complex real-world matrices. The NiCo₂O₄ NPs were synthesized via a facile plant-mediated green approach using mint (Mentha piperita) leaves extract, yielding well-dispersed, crystalline spinel structures (confirmed by FTIR, XRD, and SEM techniques). The modified electrode exhibited enhanced electrocatalytic activity toward metol oxidation, achieving a record-low detection limit (2.22 nM) and wide linear range (0.008-11.0 μM). The sensor demonstrated exceptional antiinterference capability against common contaminants (e.g., hydroquinone, catechol, metal ions) and stability (>93% signal retention after 30 days). Crucially, the NiCo₂O₄ NPs/CPE was validated in real water samples (Nile River, tap water), showing excellent recovery rates (95.5-100.25%) and reproducibility (RSD < 2%). This work not only advances the design of sustainable nanozymes for electroanalysis but also provides a field-deployable, cost-effective solution for metol monitoring in environmental and consumer safety applications.