Thiol–phenolic interactions in electropolymerized methimazole enable superior isomer discrimination for hydroquinone and catechol sensing

Abstract

A new electropolymerized methimazole (p-MMI) film-modified glassy carbon electrode was developed for simultaneous detection of hydroquinone (HQ) and catechol (CC). The p-MMI/GCE was fabricated through cyclic voltammetric deposition of methimazole, a sulfur-containing heterocyclic monomer, which formed a catalytically active interface. Electrochemical characterization revealed that the p-MMI film dramatically enhanced electron transfer kinetics: the oxidation peak currents of HQ and CC increased by 4.8- and 5.3-fold, respectively, compared to the bare GCE, while achieving a remarkable peak potential separation of 103 mV. Differential pulse voltammetry demonstrated dual linear responses for both isomers across 1.0–800 μmol L⁻¹, with detection limits of 0.6 μM (HQ) and 0.2 μM (CC) (S/N = 3). The sensor exhibited exceptional anti-interference capability against common coexisting species (e.g., ascorbic acid and Na⁺/K⁺ ions) and maintained 95.2% of the initial response after 50 cycles. Practical applicability was validated through river water analyses, yielding recoveries of 86.4–107.6% with RSD <4.3% (n = 5). Mechanistic studies suggested that the synergistic effects of methimazole's thiol groups (enhancing analyte adsorption) and conjugated imidazole rings (facilitating charge transfer) underpinned the superior performance. This work not only establishes p-MMI as a cost-effective sensing material but also provides a paradigm for transforming simple organic molecules into high-performance electrochemical interfaces through rational electropolymerization strategies.