Amino-Induced Cleavage of Electron-Communicating S-Bridge to Unlock Mixed-Valence Copper for Potent Oxidase-like Catalysis and Selective Sensing

Transition metal sites with mixed valence often coexisted in diverse catalysis, yet their precise roles remained elusive. Taking a thiadiazole-coordinated Cu nanozyme system for example, we developed ligand side-group engineering to modulate adjacent dicopper sites with different mixed Cu1+/Cu2+ states. Amino functionalization of ligand induced the cleavage of electron-communicating S-bridge connecting adjacent dicopper centers to precisely manipulate the ratio of mixed Cu1+/Cu2+ sites. Such a tailored mixed-valence composition accelerated the preferential and selective activation of O2 to O2•− through the synergistical mechanism of Cu2+-dominated adsorption of O2 and Cu1+-controlled electron transfer in the initial step of catalysis. This targeted pathway boosted the oxidase-mimicking activity of the mixed-valence nanozyme by nearly 85-fold compared to its counterpart with the adjacent S-bridged Cu centers. The outstanding oxidase-like activity, coupled with the unique affinity of mixed Cu1+/Cu2+ sites for phosphorus, further enabled highly selective and sensitive sensing of cytotoxic tris(2-carboxyethyl)phosphine with a 0.96 ppm detection limit via the complexation-dominated activity inhibition mechanism. This fundamental insight into mixed-valence synergy of metal sites provided a new perspective for designing efficient catalysts for various catalysis, sensing and beyond.