Silver-Assisted Thiolate Ligand Exchange Induced Photoluminescent Boost of Gold Nanoclusters for Selective Imaging of Intracellular Glutathione

Abstract

Metal/ligand exchange is a common strategy for precise assembly of metal nanoclusters (NCs) in organic phases. However, such a case is still not well studied in the aqueous phase. In this work we have demonstrated the silver ions assisted ligand exchange on water-soluble N-acetylcysteine (NAC) stabilized Au NCs. Silver ions may trigger both silver–gold metal exchange and silver addition on Au NCs. Unlike those well-reported silver induced photoluminescent (PL) enhancements, the processes show little changes in PL intensity. The as-obtained AuNAC@Ag NC can further promote the ligand exchange between NAC and glutathione (GSH) and induce a maximum of a 20-fold increase in PL emission at 570 nm. The enhancement was proportional to the concentration of GSH, with a linear range of 0–0.5 mM. For other thiol compounds such as cysteine, NAC, and cysteamine, no significant PL changes were observed. Cytotoxicity evaluation shows that the AuNAC@Ag NCs are biocompatible. Thus, the intracellular GSH can be specially visualized by the formation of stable AuNAC@AgGSH NCs. These results may be helpful to reveal the underlying processes of metal/ligand exchange on NCs in aqueous environment and pave a new avenue for facile design and preparation of efficient imaging probe candidates.