Detection of silver through amplified quenching of fluorescence from polyvinyl pyrrolidone-stabilized copper nanoclusters.

Silver ion detection with ultra-high sensitivity was established. We synthesized copper nanoclusters (CuNCs) with blue fluorescence through a one-pot process. Instead of a direct quencher toward the CuNCs, silver ions activated the strong oxidation from persulfate and subsequently converted divalent manganese ion into manganese dioxide (MnO2). The surface charges of MnO2 and the CuNCs brought them together and quenched the fluorescence from the latter. Due to silver ions' role as the catalyst in the process, it cycled and even a small amount leads to a significant fluorescence change. This signaling provided the determination of  silver ions in the range 5 pM~1 nM, with a detection limit of  1.2 pM. The method is selective, and its applicability was validated through practical water sample analyses.