Colorimetric sensing of ascorbic acid using the catalytic activity of β-Mn₂V₂O₇ nanoparticles as dual enzyme-mimic

Enzyme-mimetic reactions have led to the development of rapid and cost-effective visual sensors for colorimetric detection of essential molecules. In this study, β-Mn₂V₂O₇ nanoparticles were synthesized using a hydrothermal method that mimics oxidase and peroxidase activities owing to the formation of ¹O₂ and OH^• as reactive oxygen species (ROS), Mn²⁺/Mn³⁺, and V⁴⁺/V⁵⁺ surface couples in o-phenylenediamine (OPD) oxidation. The maximum velocity measured using Michaelis–Menten kinetics for the peroxidase-like activity (0.1 µM s⁻¹) was higher than that of the oxidase mimic (0.033 µM s⁻¹). Therefore, peroxidase-like system (β-Mn₂V₂O₇/OPD/H₂O₂) was used to detect vitamin C (ascorbic acid), a well-known bioactive antioxidant. Ascorbic acid (AA) inhibited the oxidation of the OPD to 2,3-diaminophenazine by scavenging OH^•, an oxidizing agent produced in a peroxidase system, and was detected based on UV–vis signal attenuation. The detection limit of AA using the colorimetric assay in the linear range of 1–10 µM was 0.47 µM (S/N = 3). Furthermore, the feasibility of the colorimetric sensor was confirmed by detecting AA in fresh juice. This study presents a dual-functional nanozyme and develops a sensitive and selective colorimetric sensor based on the peroxidase-like activity of a nanozyme to detect AA among the potential interfering components.

In this study, we developed a practical visual sensor for ascorbic acid detection as a well-known antioxidant based on the catalytic oxidation of o-phenylenediamine using β-Mn₂V₂O₇ NPs as an oxidase/peroxidase nanozyme. This sensitive colorimetric sensor was feasible for detecting ascorbic acid in orange juice.