“On–off–on” fluorescent sensor based on Ti 3 C 2 quantum dots and CoOOH nanosheets for the detection of ascorbic acid

Titanium carbide quantum dots (Ti 3 C 2 QDs) are derived from MXenes, an emerging layered two-dimensional material. Ti 3 C 2 QDs exhibit better chemical stability, dispersibility, and photoluminescence than MXenes and have great application potential in biological imaging, environmental pollution, and food safety. Ascorbic acid (AA), a key coenzyme in human metabolic pathways, plays an important role in various physiological reactions. Herein, a fluorescent sensor to detect AA is designed by combining Ti 3 C 2 QDs with cobalt oxy-hydroxide (CoOOH) nanosheets. CoOOH nanosheets, as effective fluorescence quenching agents, can considerably quench the fluorescence of Ti 3 C 2 QDs. During the detection process, AA is oxidized to dehydroascorbic acid and CoOOH nanosheets are reduced to Co 2+ and disintegrated, resulting in the recovery of the fluorescence intensity of Ti 3 C 2 QDs. Therefore, AA is detected by monitoring the degree of recovery of the fluorescence intensity of Ti 3 C 2 QDs. The fluorescent sensor exhibits a linear range of 0–100 μM and a detection limit of 0.19 μM for AA. Its recovery rates in commercial orange juice and watermelon juice are 97.12–103.95% and 94.46–107.32%, respectively, and it exhibits good detection reproducibility. This fluorescent sensor can be used to measure the AA concentration in fruits and beverages.