A noble metal-enhanced Au@CuO heterostructure with multienzyme-mimicking activities for colorimetric detection of tannic acid

Abstract

Nanozymes, serving as synthetic alternatives to natural enzymes, offer several benefits including cost-effectiveness, enzyme-like catalytic abilities, enhanced stability, adjustable catalytic activity, easy recyclability, mild reaction conditions, and environmental friendliness. Nonetheless, the ongoing quest to develop nanozymes with enhanced activity and to delve into the catalytic mechanism remains a challenge. In our research, we effectively developed Au@CuO nanocomposites (Au@CuO Nc), replicating the functions of four enzymes found in nature: peroxidase (POD), catalase (CAT), glutathione peroxidase (GPx), and oxidase (OXD). The catalytic efficiency of Au@CuO Nc for TMB oxidation (oxTMB) was approximately 4.8 times greater than that of plain Cu₂O cubes, attributed to the synergistic catalytic impact between the Au element and Cu₂O within Au@CuO Nc. Mechanistic studies revealed that the novel Au@CuO Nc nanozyme greatly enhances the decomposition of H₂O₂ to reactive oxygen species (ROS) intermediates (˙OH, ˙O₂⁻ and ¹O₂), resulting in increased POD-like activity of the single-component Cu₂O cubes. When an antioxidant like TA was added to the chromogenic system, it converted oxTMB into a colorless form of TMB, enabling further evaluation of TA. Hence, a colorimetric sensor was developed for the rapid and precise quantitative measurement of TA, demonstrating strong linearity between 0.3 and 2.4 μM and featuring a low detection threshold of 0.25 μM. Moreover, this sensor was effectively utilized for the assessment of TA in actual tea samples. This work innovatively proposes a simplified and reliable strategy for the advanced design of highly effective Cu-based nanozymes, enhancing enzyme-like reactions for simultaneous, on-site colorimetric probing of antioxidants.