"On-off-on" fluorescent sensor based on Ti₃C₂ quantum dots and CoOOH nanosheets for the detection of ascorbic acid

Titanium carbide quantum dots (Ti3C2 QDs) are derived from MXenes, an emerging layered two-dimensional material. Ti3C2 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 Ti3C2 QDs with cobalt oxy-hydroxide (CoOOH) nanosheets. CoOOH nanosheets, as effective fluorescence quenching agents, can considerably quench the fluorescence of Ti3C2 QDs. During the detection process, AA is oxidized to dehydroascorbic acid and CoOOH nanosheets are reduced to Co2+ and disintegrated, resulting in the recovery of the fluorescence intensity of Ti3C2 QDs. Therefore, AA is detected by monitoring the degree of recovery of the fluorescence intensity of Ti3C2 QDs. The fluorescent sensor exhibits a linear range of 0-100 mu M and a detection limit of 0.19 mu M 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.