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 (Cu₈ NCs) with excellent properties of high stability, large Stokes shift, and low toxicity. The molecular formula and structure of the Cu₈ 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 Cu₈ 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 Cu₈ 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 μM. Also, the fluorescence of Cu₈ NC-Al³⁺ ensemble quenched by F^– could be enhanced again upon binding additional Al³⁺. In addition, the proposed Cu₈ NC-Al³⁺ ensemble with enhanced fluorescence was used for bioimaging in vitro and in vivo. These results indicated that Cu₈ NCs are promising materials for sequential sensing and bioimaging in the future.