Facile one-pot synthesis of Au(0)@Au(I)–NAC core–shell nanoclusters with orange-yellow luminescence for cancer cell imaging

We report a facile strategy to synthesize ultrabright core–shell gold nanoclusters in one pot by using N-acetyl-L-cysteine (NAC) as both a reducing and protecting agent, in which the core is Au(0) atoms and the shell is oligomeric Au(I)–NAC complexes. The Au(0)@Au(I)–NAC core–shell nanoclusters (NCs) displayed excitation and emission bands at 340 and 590 nm, respectively. It showed a strong orange-yellow photoluminescence with a quantum yield of 14%. The thermogravimetric analysis and mass spectrometry data suggest that the as-synthesized NCs comprise mainly Au27NAC32, in which a uniquely high thiolate-to-Au ratio (1.2 : 1) endows the gold clusters better biocompatibility. The Au(0)@Au(I)–NAC core–shell NCs offered ultra-small size, excellent stability, large Stokes shift and microsecond-scale lifetime, and exhibited negligible cytotoxicity to cancer cells. Based on the excellent properties of the gold nanoclusters (AuNCs), cell experiments were conducted. Cytotoxicity studies showed that the AuNCs exhibited negligible effects in altering cell proliferation or triggering apoptosis. The as-synthesized AuNCs have been successfully applied as a photoluminescent probe for human bladder cancer cellular imaging.