Ligand density-optimized peroxidase-like activity of gold nanoclusters for colorimetric sensing of biothiols and acetylcholinesterase

Nanozymes are emerging as an attractive alternative to natural enzymes for a wide range of biological applications, but the effect of surface ligands' density on the catalytic activity of nanozymes remains largely unclear. Herein, taken gold nanoclusters (AuNCs) as a model nanozyme, glutathione-protected AuNCs (GSH-AuNCs) with three different ligand densities: low (l-AuNCs), medium (m-AuNCs), and high (h-AuNCs) were synthesized and the role of ligand density on the catalytic activity of GSH-AuNCs was systematically investigated. It was disclosed that a relatively lower ligand density is favorable for the peroxidase-like catalytic activity due to weaker steric hindrance effects. Consequently, colorimetric detection of biothiols (e.g., cysteine) and acetylcholinesterase activity was successfully achieved based on the peroxidase property of ligand density-optimized AuNCs, which exhibit a detection limit of 0.08 μM and 0.005 mU/mL, respectively. Moreover, application of the present system for detection of acetylcholinesterase activity in human serum samples was successfully demonstrated. This study provides new avenues for designing robust nanozymes with enhanced catalytic performances for application in biocatalysis as well as biosensing.