The N,S co-doped carbon dots with excellent luminescent properties from green tea leaf residue and its sensing of gefitinib

The green tea leaf residue was used as the carbon source to produce carbon dots (named as T-CDs) by combining pyrolyzation at high temperature and oxidation by concentrated H 2 SO 4 . Owing to the co-doping of S and N, T-CDs possessed high fluorescence quantum yield up to 14.8%. The fluorescence of the T-CDs was stable to the environmental pH, ionic strength and ultraviolet radiation, but sensitive to temperature with switchable intensity between 15 °C and 65 °C. The fluorescence of T-CDs was also found to be quenched by gefitinib via the inner-filter effect. Thus, T-CDs were used as the fluorescence sensor for gefitinib determination with good linearity in the range of 0.1 μg/mL to 20 μg/mL with satisfactory accuracy. The proposed T-CDs were obtained based on waste recycling of tea leaf residue for sustainability, and this strategy widened the applications of CDs.