Ce⁴⁺/Ce³⁺ as the switch of AIE-copper nanoclusters for highly selective detection of ascorbic acid in soft drinks

An ultrasimple "turn-on" sensor for indirectly detecting ascorbic acid (AA) was prepared using N-acetyl-L-cysteine stabilized copper nanoclusters (NAC-CuNCs) via the AIE (aggregation-induced emission) effect controlled by Ce⁴⁺/Ce³⁺ redox reaction. This sensor fully utilizes the different properties of Ce⁴⁺ and Ce³⁺. Non-emissive NAC-CuNCs were synthesized by a facile reduction method. NAC-CuNCs easily aggregate in the presence of Ce³⁺ due to AIE, resulting in fluorescence enhancement. However, this phenomenon cannot be observed in the presence of Ce⁴⁺. Ce⁴⁺ possesses strong oxidizing ability and produces Ce³⁺ by reacting with AA via a redox reaction, followed by switching on the luminescence of NAC-CuNCs. Moreover, the fluorescence intensity (FI) of NAC-CuNCs increases with the concentration of AA in the range of 4-60 µM, with the limit of detection (LOD) as low as 0.26 µM. This probe with excellent sensitivity and selectivity was successfully used in the determination of AA in soft drinks.