Surface-Engineered Copper Oxide with Enhanced Peroxidase-Mimic Activity for Ag⁺ Detection

Developing convenient enzyme-mimic colorimetric detection methods is essential for the long-term and systematic safety management of Ag⁺ pollution, where nanozyme stability and catalytic activity govern detection performance. In this work, we employed a surface-engineering strategy on copper oxides using trithiocyanuric acid (TTCA) as an electron-injection reagent. Partial etching of Cu²⁺ was followed by in situ reductive coordination with the C═S groups of TTCA, generating a surface coating of poly-TTCA/Cu⁺ and TTCA/Cu⁺ species. This surface engineering approach significantly enhanced both the peroxidase-mimic (POD-mimic) activity and catalytic stability of the copper oxides. The introduced unsaturated Cu⁺···S═C coordination moieties were identified as critical for efficient H₂O₂ activation to produce reactive oxygen species (·OH, ·O₂^-, and ¹O₂). A highly sensitive and selective colorimetric platform was then established for Ag⁺ detection, achieving a detection limit of 0.02 μM and successfully applied to actual water samples. The detection mechanism involves Ag⁺-mediated structural disruption and reconstruction, leading to the passivation of the POD-mimic activity. Our surface-engineering strategy for improving the POD-mimic performance deepens the understanding of the structure-activity-detection relationship in nanozymes, presenting a valuable pathway for advancing enzyme-mimic optimization for diverse applications.