Aluminum-Enhanced Fluorescence of Cu8 Nanoclusters: An Effective Method for Sensitive Detection of Fluoride in Aqueous and Bioimaging

Here, we report glutathione-protected water-soluble copper nanoclusters (Cu-8 NCs) with excellent properties of high stability, large Stokes shift, and low toxicity. The molecular formula and structure of the Cu-8 NCs were confirmed through good agreement between spectroscopic results and theoretical calculations. The origin of optical properties and chemical stability of the Cu8 NCs was determined through natural bond orbital analysis combined with time-dependent density functional theory calculations. It was found that the fluorescence emission and quantum yields of Cu-8 NCs could be effectively enhanced by aluminum(III) ions (Al3+) through the aggregation-induced enhanced emission mechanism. On the basis of the strong reaction of Al3+ with F-, the enhanced fluorescence of the obtained Cu-8 NC-Al3+ ensemble could be selectively turned off by fluoride ions (F-), achieving highly sensitive detection of F- in aqueous with a detection limit of 0.16 mu M. Also, the fluorescence of Cu-8 NC-Al3+ ensemble quenched by F- could be enhanced again upon binding additional Al3+. In addition, the proposed Cu-8 NC-Al3+ ensemble with enhanced fluorescence was used for bioimaging in vitro and in vivo. These results indicated that Cu-8 NCs are promising materials for sequential sensing and bioimaging in the future.