Partial Oxidation Boosts Ru Nanoparticles with Excellent\nOxidase-Mimicking Activity for Melatonin Colorimetric Detection

It\nis highly desirable but still remains challenging to tune nanozymes\nwith superior catalytic activity via simple operation. Herein, the\noxidase-like activity of Ru nanoparticles supported on porous carbon\n(Ru/PC) was significantly modulated via a facile partial oxidation\nprocess. Due to the small size, uniform dispersion, high electron\ndensity on the surface, as well as abundant interfacial heterostructure\nbetween Ru and RuO<sub>2</sub>, the partially oxidized Ru/PC (P–Ru/PC)\nshowed excellent oxidase-mimicking activity in triggering 3,3′,5,5′-tetramethylbenzidine\n(TMB) oxidation, with a low K<sub>m</sub> of 0.138 mM and a high <i>V</i><sub>max</sub> of 2.82 × 10<sup>–7</sup> M·s<sup>–1</sup>. Theoretical calculations reveal that both the absorption\nand subsequent activation of molecular oxygen are more favorable on\nthe interfacial heterostructure of P–Ru/PC than on the Ru/PC\nsurface. Moreover, the oxidase-like activity of P–Ru/PC was\nfound to be suppressed by melatonin, along with a fading color of\noxidized TMB (TMB<sub>ox</sub>). As a result, a novel colorimetric\nsystem consisting of P–Ru/PC and TMB was established for melatonin\ndetection for the first time, which shows a wide linear range of 10–220\nμM and a low detection limit of 0.023 μM. This work not\nonly provides a simple but smart strategy of interface engineering\nto tune the oxidase-like activity of Ru/PC, but also expands the application\nof Ru oxidase mimics in pharmaceutical analysis.