Synergistic oxygen vacancy and multivalence in Co/Cu-ZIF/V₂O₅ nanozyme enable ultrasensitive colorimetric detection of ascorbic acid and epigallocatechin gallate.

Sensitive detection of antioxidants like ascorbic acid (AA) and epigallocatechin gallate (EGCG) in tea is crucial for quality control. To overcome the limitations of natural peroxidases, we designed a Co/Cu-ZIF/V₂O₅ nanozyme via vanadium-doped defect engineering. This strategy created intertwined V₂O₅ nanofibers synergizing with multivalent metal species (Cu0/Cu+/Cu2+, Co2+/Co3+), yielding exceptional peroxidase-like activity for TMB oxidation. The enhanced activity originates from abundant oxygen vacancies and multivalent redox couples, which facilitate H₂O₂ dissociation into hydroxyl radicals (·OH) as the key oxidizing species. Kinetic analyses demonstrated enhanced substrate affinities (Kₘ for TMB: 0.059 mM, for H₂O₂: 1.62 mM), with Vₘₐₓ approximately 9-fold higher than HRP. Based on ·OH competitive inhibition, a dual-analyte colorimetric sensor was developed for AA and EGCG with detection limits of 6.84 μM and 0.007 μM, respectively, providing a robust nanozyme platform for monitoring bioactive compounds in complex food matrices.