Innovative spectrofluorimetric determination of vildagliptin based on a “switch off/on” NS-doped carbon dot nanosensor

A simple, fast, and green one-step microwave pyrolysis approach was proposed for the synthesis of highly fluorescent nitrogen/sulfur-doped carbon dots (NS-CDs). The proposed NS-CDs were prepared in only one minute from citric acid and thiosemicarbazide. In the presence of Cu2+, the fluorescence of NS-CDs was significantly quenched ("turn off") through the formation of a non-fluorescent NS-CDs/Cu2+ complex. This designed sensor could be applied for label-free determination of vildagliptin based on the competition between vildagliptin and the functional groups on NS-CDs for Cu2+ complexation, and hence NS-CD fluorescence recovery ("turn on"). Under the optimized conditions, the developed probe (NS-CDs/Cu2+) demonstrated a good sensing performance for vildagliptin with linearity in the range of 45-240 μM and a detection limit of 13.411 μM. Owing to its sensitivity, this sensor was successfully applied for vildagliptin determination in human urine samples.