Silver nanocluster-based fluorescent sensors for sensitive detection of Cu(II)

In this work, we report the first application of water-soluble fluorescent Ag nanoclusters in fluorescent sensors. The fluorescence of poly(methacrylic acid) (PMAA)-templated Ag nanoclusters was found to be quenched effectively by Cu(2+), but not when other common metal ions were present. By virtue of the specific response toward the analyte, a new, simple, and sensitive fluorescent method for detecting Cu(2+) has been developed based on Ag nanoclusters. The present assay allows for the sensing of Cu(2+) in the range of 1.0 x 10(-8) M to 6.0 x 10(-6) M with a detection limit as low as 8 nM at a signal-to-noise ratio of 3. The quenching mechanism was discussed based on the absorption and fluorescence spectroscopy studies, which suggested that Cu(2+) quenched the emission by binding with the free carboxylic groups of PMAA polymers that surround the emissive Ag nanoclusters. In addition, the response of Ag nanoclusters toward Cu(2+) was found to be reversible, which further made the present system attractive for sensor applications. The present study shows a promising step toward the application of fluorescent metal nanoclusters, which may also serve as a foundation for the further design and understanding of these novel materials.