Amino-induced cleavage of the electron-communicating S-bridge to unlock mixed-valence copper for potent oxidase-like catalysis and selective sensing.

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