Tollens Reagent-Directed Flower-like α-Ag ₃ VO ₄ Nanozyme for Signal-Amplified Colorimetric Detection of Epigallocatechin Gallate

Oxidase-like colorimetric sensors based on crystalline vanadates show great potential for polyphenol detection without H₂O₂. However, most inorganic nanozymes possess multienzyme activities and follow the "on-to-off" sensing mode, limiting sensitivity and accuracy in complex matrices. Herein, a flower-like α-Ag₃VO₄ nanozyme was synthesized via a Tollens reagent-mediated method. Distinct from conventional vanadate-based materials, it activates O₂ molecules adsorbed on its oxygen-defective (010) surface through 0.86 eV energy transfer, thereby exerting exclusive oxidase-like activity with O₂^•- and ¹O₂ as electron acceptors. EGCG accelerates charge transfer and boosts catalytic activity by over 6-fold within 1 min, allowing for an "off-to-on" colorimetric sensor. This unique phenomenon enables the construction of a rapid colorimetric sensor based on an "off-to-on" signal model, which differs fundamentally from reported nanozyme-based colorimetric systems for reducing targets. Compared with the widely used aluminum chloride method (detection limit, LOD = 3.54 μM), the proposed sensor exhibits excellent specificity, superior sensitivity (LOD = 0.16 μM) for EGCG, and comparable accuracy in real sample analysis. This work not only provides a synthetic chemistry approach to tailor the enzyme-like activity of inorganic materials but also offers a promising platform for the sensitive detection of reducing polyphenols.