Recent decades have witnessed the rapid progress of nanozymes and their high promising applications in catalysis and bioclinics. However, the comprehensive synthetic procedures and harsh synthetic conditions represent significant challenges for nanozymes. In this study, monodisperse, ultrasmall gold clusters with peroxidase-like activity were prepared via a simple and robust one-pot method. The reaction of clusters with H2O2 and 3,3′,5,5′-tetramethylbenzidine (TMB) followed the Michaelis-Menton kinetics. In addition, in vitro experiments showed that the prepared clusters had good biocompatibility and cell imaging ability, indicating their future potential as multi-functional materials.

The stimuli response of nanomaterials represents a highly appealing characteristic, whereas the practical applications (in catalysis, biosensing etc.) are largely restricted by the limited understanding on the recognition mechanism. Herein, we report a pH‐regulated size evolution from atomically precise Au nanoclusters (NCs) to plasmonic nanoparticles (NPs). The spectral monitoring demonstrates a three‐stage aggregative growth pathway. First, the non‐covalent interactions among the exterior oligopeptide ligands are gradually enhanced with the increased alkalinity, and then the Au−S bonding is partially disrupted, with the exposed Au atoms aggregating to form relatively larger, polydisperse clusters under weak alkaline conditions. Finally, size‐redistribution occurs slowly under strong alkaline conditions to form the plasmonic particles. The controllable transition sheds light on the transition characteristics from molecular state to metallic state of Au nanomaterials.