Bifunctional Cu0.4Co2.6O4 nanocube induced by Cu substitution with superior peroxidase-like activity: Application in hydroquinone multi-mode detection

Hydroquinone (HQ), a phenolic compound, poses substantial risks to human health due to its low degradability and high toxicity. Consequently, developing sensitive, accurate, and portable approaches for monitoring HQ is of significant importance. Herein, M-substituted (M=Cu, Mn, Ni, and La) Co₃O₄ nanocube (Co₃O₄ NC) was developed for improving the peroxidase-like activity of Co₃O₄ NC. Among these, Cu-substituted Co₃O₄ NC (Cu_0.4Co_2.6O₄ NC) exhibited optimal peroxidase-like performance. Investigation into the catalytic mechanism revealed that the generation of hydroxyl radical and the increase of superoxide anion significantly enhanced the catalytic activity of Cu_0.4Co_2.6O₄ NC. Cu_0.4Co_2.6O₄ NC could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) with H₂O₂ to form a blue-color product. In the existence of HQ, the chromogenic reaction of TMB was inhibited due to the competition between HQ and TMB for the reactive oxygen species in the catalytic system. Additionally, a smartphone-mediated portable hydrogel sensor was integrated with color change to facilitate on-site detection. Furthermore, Cu_0.4Co_2.6O₄ NC served as an electrocatalyst for electrochemical analysis of HQ. Considering these findings, we proposed a colorimetrical, hydrogel, and electrochemical multi-mode sensor for detecting HQ, showing wide linear ranges and low detection limits. The multi-mode sensor features self-verification for more reliable results and is suitable for various analysis conditions. It successfully determined HQ in real water samples, accompanied by consistent results with HPLC. This work not only provides an efficient pathway for developing nanozymes with superior catalytic properties but also demonstrates application potential in environmental protection.