A non-oxidation reduction strategy for highly selective detection of ascorbic acid by “on-off-on” photoluminescence switches

Great progress was made to detect ascorbic acid (AA) based on the photoluminescent nanoprobes/oxidant complexes by using the reducibility of AA. However, some reducing substances including cysteine and glutathione disturbed the accuracy of AA assay. Herein, a non-oxidation reduction regulation strategy was fabricated to construct a novel "on-off-on" photoluminescence model for highly selective determination of AA. Initially, copper nanoclusters capsulated into zeolitic imidazolate framework-8 (CuNCs@ZIF-8) was achieved. And then inorganic phosphate ions quenched the emission of CuNCs@ZIF-8 owing to the decomposition of ZIF-8 shell, rendering the signal in "turn-off" state. The linear range for phosphate ions was 1.0–60 μM with LOD of 0.35 μM. Interestingly, upon introducing AA into CuNCs@ZIF-8/phosphate, the emission of CuNCs@ZIF-8 recovered possibly due to the electronegativity improvement of metal core and surface rigidified through hydrogen bond interaction, and the system signal was "turned-on". The LOD of AA was as low as 51 nM in a good linear range from 0.1 to 40 μM. Furthermore, CuNCs@ZIF-8 were used for AA detecting in tablets, beverages, and fresh fruits with the satisfactory recoveries from 96% to 104%. More importantly, a paper-based analytical device containing CuNCs@ZIF-8/phosphate were evaluated for the visual sensing of AA in food safety.