The density of surface ligands regulates the luminescence of thiolated gold nanoclusters and their metal ion response

The fascinating luminescence properties of gold nanoclusters (AuNCs) have drawn considerable research interests, and been widely harnessed for a wide range of applications. However, a fundamental understanding towards ligand density's role in the luminescence properties of these ultrasmall AuNCs remains unclear yet. In this communication, through systematic investigation of surface chemistries of glutathione-protected AuNCs (GSH-AuNCs) with different density of GSH as well as other thiolates, it is discovered that the density of surface ligands can significantly regulate the luminescence properties of AuNCs. Fluorescence lifetime spectroscopy and X-ray photoelectron spectroscopy showed that AuNCs with a higher density of electron-rich ligands facilitate their luminescence generation. Moreover, differences in the surface coverage of AuNCs can also affect their interactions with foreign species, as illustrated by significantly different fluorescence quenching capability of GSH-AuNCs with different ligand density towards Hg²⁺. This study provides new insight into the intriguing luminescence properties of metal NCs, which is hoped to stimulate further research on the design of metal NCs with strong luminescence and sensitive/specific responses for promising optoelectronic, sensing and imaging applications.