Photo-responsive oxidase-like nanozyme based on a vanadium-docked porphyrinic covalent organic framework for colorimetric L-Arginine sensing

This study reports the development of a vanadium-docked porphyrinic covalent organic framework as a novel class of highly polar photoactive materials. Thanks to its extended π-electron conjugation and high chemical stabilities, this framework can serve as an oxidase-Like photo-nanozyme for photocatalytic oxidation of o-phenylenediamine (o-PDA) and a colorimetric substrate for the production of the yellow-colored oxidized o-PDA (o-PDAox). The physicochemical properties of the as-prepared photo-nanozyme were characterized by several analytical techniques. Its enhanced light harvesting and charge separation and transfer were also verified by electrochemical and spectroscopic analysis. This photo-nonenzymatic colorimetric assay was applied for the sensitive L-Arginine (L-Arg) detection as a typical amino acid in the linear range of 8.1 nM-330 μM with a limit of detection (LOD) of 3.5 nM. The findings of this research confirmed the safety and feasibility of the proposed photo-nonenzymatic colorimetric sensing strategy for the detection of L-Arg and other similar biomolecules in food samples. Kinetic investigation revealed that the photo-responsive oxidase mimic exhibits satisfactory Km (0.47 mM) and Vmax (42.0 μM/s) values. This work broadened our insight into the development of modified porphyrinic-COF-based visible light-responsive oxidase-like photo-nanozyme for environmentally friendly colorimetric biosensing.