Two-dimensional vanadium oxysulfide (VSO_x) nanosheets exhibiting oxidase-peroxidase-mimetic activity for efficient...

Two-dimensional nanozymes with multi-enzyme mimetic activity have emerged as promising alternatives to natural enzymes for chemical sensing, owing to their superior stability, low cost, and tunable catalytic properties. Among them, nanozymes exhibiting oxidase- and peroxidase-like activities are particularly attractive for developing versatile and reagent-flexible sensing platforms. However, despite the prevalence of multi-enzyme mimics in the literature, most reported nanozyme-based sensors utilize only a single fixed catalytic configuration under rigid assay conditions, which can limit analytical flexibility. Herein, we demonstrate a tunable VSO_x nanozyme platform capable of operating in either an oxidase- or a peroxidase-like configuration, providing an adaptable colorimetric strategy for ascorbic acid quantification. In this context, engineering 2D nanostructures with intrinsic bifunctional catalytic activity remains a challenge. Therefore, the key problem addressed in this work is the development of a tunable colorimetric sensing platform that can operate in oxidase-like or peroxidase-like configurations for Ascobic Acid (AA) detection.

Two dimensional Vanadium oxysulfide (VSOx) nanosheets were synthesized and systematically evaluated as a bifunctional nanozyme exhibiting both oxidase-mimetic (OD) and peroxidase-mimetic (POD) activities. The nanosheets catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation through two catalytic configurations: a hydrogen peroxide-independent route (OD mode) and a hydrogen peroxide-activated route (POD mode), establishing a tunable colorimetric sensing platform. Analytical evaluation demonstrated that the POD pathway achieved a limit of detection (LOD) of 0.17 μM, while the OD pathway exhibited significantly enhanced sensitivity with an LOD of 0.009 μM for ascorbic acid. The superior catalytic performance is attributed to the two-dimensional architecture, which provides abundant surface-exposed active sites, and to the synergistic redox behavior of vanadium centers within the oxysulfide lattice, facilitating efficient electron transfer. The platform showed excellent analytical reliability, delivering recoveries of 98.2-104.0% in real samples, including orange juice and blood serum.

This work introduces a tunable-pathway nanozyme system that integrates oxidase- and peroxidase-like activities within a single 2D material, enabling flexible and highly sensitive detection of ascorbic acid. The ability to operate with or without hydrogen peroxide represents a useful advancement in nanozyme-based sensing. This strategy provides a robust, enzyme-free platform with practical applicability for food safety and clinical diagnostics.