Fluorescence “turn-on” of sanguinarine-templated copper nanoclusters for sensing ascorbic acid in orange drinks and tablets

The quantitative determination of ascorbic acid (AA) in food and drugs is beneficial to guide diet choices and ensure drug safety. In this study, using a natural small molecule sanguinarine (SAN) as the template and AA as the reducing agent, a novel type of fluorescent copper nanoclusters (SAN-CuNCs) was synthesized and characterized. MnO 2 nanosheet (MnO 2 NS) was additionally utilized to develop a fluorescence “turn-on” sensor for AA. The fluorescence of SAN-CuNCs was quenched by MnO 2 NS. Upon addition of AA, the degradation of MnO 2 NS led to the recovery of the fluorescence. Under optimal conditions, the AA sensor exhibited an excellent linearity (R 2  = 0.9916) within the concentration range of 25–400 μM. The fluorescent sensor was successfully employed for the accurate analysis of AA in four orange drinks and two vitamin C tablets. This study demonstrated that the availability of the sensor, while also providing valuable insights into the development of natural products.