Cu2+ enhanced fluorescent Ag nanoclusters with tunable emission from red to yellow and the application for Ag+ sensing

In this work, the water-soluble fluorescent Ag nanoclusters (DPA@Ag NCs) were first prepared based on D-Penicillamine (DPA) as a stabilizer, however, the fluorescence quantum yield (QY) of DPA@Ag NCs was very low, then Cu2+ was employed to improve the fluorescence QY and the doped Ag nanoclusters with Cu2+ (DPA@Ag/Cu NCs) were obtained. The study showed that the QY increased fourfold and the emission of nanoclusters changed from red to yellow after addition of Cu2+. The reason for change of fluorescent properties was attributed to the change of self-assembly structures caused by adding Cu2+ into reaction system, leading to the aggregation-induced emission enhancement (AIEE) effect and enhancing the band gap (Eg) between the HOMO and LUMO in nanoclusters. Subsequently, a fluorescent Ag+ sensor with high sensitivity and selectivity was established based on the DPA@Ag/Cu NCs as probes in aqueous solution. Experiments showed that the Ag+ could significantly quench the fluorescence of DPA@Ag/Cu NCs under experimental conditions, and there was a good linear relationship between the fluorescent intensity quenching value and Ag+ concentration in the range of 0.05–800 μM, and the limit of detection (LOD) was 0.03 μM (3σ/k). Meanwhile, most of common ions had no effect on the experimental results under the same conditions. In addition, the sensor was successfully applied on the detection of Ag+ in real water samples, and the recovery rate was 80.3–99.0%.