Although numerous sensors have been successfully fabricated for the detection of various heavy metal ions by employing fluorescent gold nanoclusters (AuNCs) as nanoprobes, serious cross-interference often occurs when these ions coexist in samples, which results in glaring errors in quantification. In this study, glutathione-protected AuNCs (GSH-AuNCs) were synthesized and found to respond to both Cu2+ and Hg2+ via fluorescence suppression. Intriguingly, addition of Ag+ to GSH-AuNCs could completely inhibit the quenching effect of Hg2+ while not affecting the Cu2+-mediated quenching process. Ag+ can combine with Au+ on the surface of AuNCs to form a strong Ag+-Au+ metallic bond, which disrupts the interaction between Hg2+ and Au+ and thus eliminates the corresponding quenching effect. Based on this phenomenon, a simple sensing approach for highly selective and sensitive detection of Cu2+ in aqueous solution was developed using the GSH-AuNC/Ag+ complex as a fluorescent turn-off nanoprobe. The proposed method exhibited good linearity in the concentration range 0.02-10 μM with a limit of detection of 12 nM. This assay was demonstrated to be suitable for determination of Cu2+ in real water samples even in the presence of Hg2+, showing great promise as a tool for assessment of environmental security and drinking water quality.
Keywords: Fluorescence quenching; Gold nanocluster; Heavy metal ion; Metallophilic interaction; Selectivity.
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