Switch-on fluorescence sensor for ascorbic acid detection based on MoS2 quantum dots-MnO2 nanosheets system and its application in fruit samples

In this work, molybdenum disulfide quantum dots (MoS₂ QDs) were firstly prepared by hydrothermal method using sodium molybdate and glutathione as precursors, and applied in ascorbic acid detection. When joining MnO₂ nanosheets into MoS₂ QDs solution, they produced an obvious fluorescence quenching, which should be due to inner filter effect (IFE). Meanwhile, the fluorescent probe was formed. Interestingly, we found that this quenching phenomenon disappeared with the addition of ascorbic acid. In other words, the fluorescence gradually restored. This recovery phenomenon is mainly due to the reduction effect of ascorbic acid for MnO₂ nanosheets. Under the optimum conditions, the limit of detection (LOD) of 39 nmol/L for ascorbic acid was achieved with a linear range of 0.33-5.00 μmol/L. The repeatability was better than 5.0% for ascorbic acid in both standard and fruit samples (n=3). Moreover, the as-fabricated fluorescent sensing system was successfully employed to detect the ascorbic acid levels in hawthorn and jujube with satisfactory results.