Fe3+ assisted water-soluble nickel nanocluster for the “on-off-on” fluorescence determination of ascorbic acid

An “on-off-on” fluorescent sensor has been constructed to determine ascorbic acid (AA) based on water-soluble glutathione-decorated nickel nanoclusters (NiNCs) with assistance of trivalent iron ions (Fe3+). The fluorescence could be effectively quenched (off) upon adding Fe3+ due to aggregation-caused quenching (ACQ) and the internal filtering effect (IFE). Meanwhile, the fluorescence of NiNCs–Fe3+ systems could be again recovered (on) after introducing AA, which is attributed for the redox reaction between Fe3+ and AA. The sensor can detect AA in the linear range of 20–200 μmol/L with a LOD of 7.45 μmol/L. More importantly, the proposed approach has been successfully applied for the detection of AA content in commercially available tablets and beverages as well as in common fruits with satisfactory recovery ranges, suggesting the potential sensing platform for AA detection. Therefore, the prepared sensor offers distinct advantages including low cost, simple operation, good sensitivity, and high selectivity, which has a broad application prospect of metal nanoclusters.