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

It is highly desirable but still remains challenging to tune nanozymes with superior catalytic activity via simple operation. Herein, the oxidase-like activity of Ru nanoparticles supported on porous carbon (Ru/PC) was significantly modulated via a facile partial oxidation process. Due to the small size, uniform dispersion, high electron density on the surface, as well as abundant interfacial heterostructure between Ru and RuO2, the partially oxidized Ru/PC (P–Ru/PC) showed excellent oxidase-mimicking activity in triggering 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, with a low Km of 0.138 mM and a high Vmax of 2.82 × 10–7 M·s–1. Theoretical calculations reveal that both the absorption and subsequent activation of molecular oxygen are more favorable on the interfacial heterostructure of P–Ru/PC than on the Ru/PC surface. Moreover, the oxidase-like activity of P–Ru/PC was found to be suppressed by melatonin, along with a fading color of oxidized TMB (TMBox). As a result, a novel colorimetric system consisting of P–Ru/PC and TMB was established for melatonin detection for the first time, which shows a wide linear range of 10–220 μM and a low detection limit of 0.023 μM. This work not only provides a simple but smart strategy of interface engineering to tune the oxidase-like activity of Ru/PC, but also expands the application of Ru oxidase mimics in pharmaceutical analysis.