Adsorption Isotherm Analysis for Hybrid Molecularly Imprinted Polymeric Gold-Decorated Nanoparticles Suitable for Reliable Quantification of Gluconic Acid in Wine

A class of hybrid molecularly imprinted polymeric nanoparticles (nanoMIPs) comprising the in situ formation of gold nanoparticles (AuNPs) immobilised in a molecularly imprinted D-gluconate polymer has been designed with the objective of attempting the electro-chemical quantification of gluconic acid (GA) in a wine setting. The imprinted polymers were synthesised in the presence of AuNP precursors in a pre-polymerisation mixture, which were confined to one another during the polymerisation of the chains. This allowed the formation of hybrid electroactive responsive imprinted nanoparticles (hybrid AuNPs@GA-nanoMIP), which exhibited enhanced electron conductivity. The morphological characterisation of the produced nanoMIPs revealed a fully decorated Au spherical surface of 200 nm in diameter. This resulted in a large active surface area distribution, as well a pronounced electrochemical peak response at the commercial screen-printed platinum electrode (SPPtE), accompanied by enhanced electron kinetics. The AuNPs@GA-nanoMIP sensor demonstrated the ability to detect a broad range of GA concentrations (0.025–5 mg/mL) with exceptional selectivity and reproducibility. The calibration curves were fitted with different isotherm models, such as the Langmuir, Freundlich and Langmuir–Freundlich functions. Moreover, the efficacy of the detection method was demonstrated by the recovery rates observed in real samples of Italian red wine. This research contributes to the development of a robust and reliable electrochemical sensor for the on-site determination of gluconic acid in food analysis.