Coordination-Tuned Iridium Single-Atom Nanozymes Boost Multienzyme Activity for Colorimetric Sensing

Precisely manipulating the coordination environment in single-atom nanozymes (SAzymes) remains a critical challenge in breaking the intrinsic activity ceiling, thus limiting the multifunctionality of current enzyme-mimetic catalysts. In this study, iridium SAzymes featuring an asymmetric Ir-N₃S₁ coordination motif (Ir-S/N-C) were prepared by adding sulfur to a traditional Ir-N-C framework. Density functional theory calculations revealed that this symmetry-breaking coordination design enabled the fine modulation of the local electronic structure of the isolated iridium centers, which upshifted the d-band center and substantially reduced the energy barrier for O₂ activation. Ir-S/N-C exhibited markedly enhanced oxidase- and peroxidase-like activities, and a glutathione-oxidase-like functionality emerged, thus achieving integrated multienzyme-like catalysis within a single-atom platform. Notably, the strong intrinsic oxidase activity allowed the construction of a self-sufficient H₂O₂-free colorimetric sensing system for antioxidants and organophosphate pesticides, delivering high sensitivity and selectivity in complex sample matrices. Overall, this study demonstrated asymmetric sulfur coordination as a promising coordination-engineering strategy for modulating the electronic structure of single-atom sites and highlighted its effectiveness in developing high-performance multifunctional SAzymes.