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–N 3 S 1 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 O 2 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 H 2 O 2 ‐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.