Fluorescent Copper Nanoclusters for the Iodide-Enhanced Detection of Hypochlorous Acid

In this work, fluorescent copper nanoclusters (CuNCs) have been fabricated with ascorbic acid (AA) as reductant and polyvinyl pyrolidone (PVP) as scaffold in aqueous solution for the on-site detection of hypochlorous acid (HClO) with high sensitivity and selectivity. The CuNCs showed a specific fluorescence quenching toward HClO compared with other reactive oxygen species and ions that are found widely in the environment. The CuNCs also exhibited a good linear fluorescence quenching effect on HClO with a limit of detection at 55 nM. The mechanism has been investigated and was attributed to the oxidation of reduced Cu on the surface of CuNCs by HClO. Surprisingly, the fluorescence intensity of the probe was more responsive to HClO in the presence of excessive iodide ions (I-), with a lower detection limit of 19 nM. In acidic conditions, iodine (I-2) was generated by HClO oxidation and subsequently reacted with Cu atoms on the surface of CuNCs to form cuprous iodide (CuI) precipitation. This resulted in surface defects on the CuNCs, which further significantly reduced the fluorescence intensity of the CuNCs. Under the influence of the reaction mechanism, the order of excessive I- and HClO addition affects the linear range and detection limit of the probe. Because these CuNCs have shown excellent performance as a fluorescent probe, they have been further successfully applied for real-time quantitative detection of HClO in practical samples, and I- can also be used as a "sensitizer" in HClO sensing.