Exploration of pH-responsive carbon dots for detecting nitrite and ascorbic acid

Detections of carcinogen and vitamins are generally recognized to be meaningful, especially for nitrites (NO2−) and ascorbic acid (AA). Here blue-fluorescence carbon dots (CDs) with the quantum yield of 11.83% were successfully synthesized by using folic acid and nicotinic acid, and their surfaces were identified to be abundant in the functional groups of amide, carboxyl and hydroxyl. Importantly, the amide on the surfaces of CDs showed the interactions with the nitrites and formed the complex, thus resulting in their quenched fluorescence. To be specific, the fluorescence intensity of CDs proportionally decreased by adding the increased amounts of NO2− from 8 to 800 μM, and achieved the detection of NO2− at a detection limit of 21.2 µM. Moreover, further introducing ascorbic acid could prevent CDs with NO2− to form the complex and recover their fluorescence, and thus providing the new avenue of assaying AA with the generally favorable linear range of 0.1–800 μM, while its related detection limit was 50 µM. In addition, the synthesized CDs exhibited the satisfactory sensitivity toward different pH values, demonstrating their potential of sensing pH. Consequently, the proposed CDs here may provide a new way of monitoring NO2− and AA in the target samples.