Synthesis and evaluation of zinc oxide nanomaterials for the electrochemical detection of hydroxybenzoic acid

Using an aqueous solution of Zn(NO₃)₂·6H₂O as a precursor, ZnO nanoparticles (ZNPs) were synthesized with spherical shape and size using the controlled precipitation method. The nanoparticles had hexagonal wurtzite structure with Zincite phase and space group 186: P63mc, as confirmed by dispersive energy of X-rays. Crystallite size of 18 nm is small enough to provide a high density of grain boundaries. The scanning electron microscopy revealed that the particles were composed of well-oriented nano-spheres and the optical analysis indicated that the particles had a direct optical band gap of 2.8 eV. The high surface area to volume ratio, wide band gap, biocompatibility, catalytic activity, easy modification, and environmentally friendly nature make the ZNPs an excellent material for sensitive, selective, and stable electrochemical sensors. This study addresses the electrochemical sensing of 4-Hydroxybenzoic acid (4-HBA), an aromatic organic acid derived from benzoic acid, known for its neuroprotective, anticancer, and cardioprotective properties, utilizing ZNPs. 4-HBA and similar metabolites have shown diagnostic value in critically sick patients and those with post-COVID-19 syndrome, acting as biomarkers for numerous illnesses and showing pathological processes through blood concentration variations, also after green tea ingestion 4-HBA is a major catechin metabolite. The fabricated electrochemical sensor for the detection of 4-HBA showed a sensitivity of 4.14 μA cm⁻² μM⁻¹ with a 0.5 µM detection limit.