Highly efficient fluorescence probe for copper (II) ions based on gold nanoclusters supported on wool keratin

A highly efficient fluorescence gold nanoclusters probe for copper (II) (Cu2+) ions among various ions has been prepared through wool keratin as chelating and reducing agent. The main features of fluorescent gold nanoclusters supported on wool keratin (AuNCs@WK) probe are the high fluorescence in aqueous solution, the simplicity of synthesis and the hypotoxicity for living cells. The fluorescence probe exhibits high stability of pHs and shows more sensitivity under acidic condition. Upon exposure to various metal irons, only AuNCs@WK system with Cu2+ ions shows a fluorescence turnoff response changing from red to blue under UV light, which lead to the dramatically decreased fluorescent intensity of AuNCs@WK at 690 nm. Moreover, the high sensitivity of AuNCs@WK around 1 µM meets the need of detection standards. The slope of Stern–Volmer plot at low concentration of Cu2+ ions is greater than it at high concentrations, which indicates the aggregated AuNCs are from small amounts to large numbers with the increasing concentration of Cu2+ ions. The design mechanism of AuNCs@WK probe is the coordination of reactive groups to produce the complex (wool keratin-Cu-wool keratin) at 1:2 between Cu2+ ions and fluorescence probe. Furthermore, the cytotoxicity in cells indicates that AuNCs@WK system is safe for the selective imaging of copper ions in living cells.