Aqueous synthesis of N-heterocyclic carbene-protected gold nanoclusters with intrinsic antibacterial activity

Abstract

N-Heterocyclic carbene (NHC) is regarded as a versatile ligand to stabilize gold nanoclusters (AuNCs) via forming strong Au-C bonds. However, reports on NHC-protected AuNCs are rare, especially in aqueous systems. Herein, we present a facile one-step approach to fabricate hydrophilic AuNCs in an aqueous medium using a NHC-based ligand as both a reducing agent and stabilizer. The coordination mechanism involves formation of covalent Au-C bond, as evidenced by nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy. Taking advantages of their ultrasmall size and positively charged surface, these AuNCs can readily penetrate the cell wall and accumulate in bacteria, leading to an obvious increase in intracellular reactive oxygen species. Accordingly, these AuNCs have wide-spectrum antibacterial activity toward Staphylococcus aureus (gram-positive bacterium), Escherichia coli (gram-negative bacterium), and Candida albicans (fungi).