Heterogeneous synthesis of nitrogen-doped carbon dots prepared via anhydrous citric acid and melamine for selective and sensitive turn on-off-on detection of Hg (II), glutathione and its cellular imaging

Abstract Herein a new kind of convenient, low-cost, environmentally friendly and high-output heterogeneous one step synthesis of nitrogen-doped carbon dots (N-CDs) was developed by reacting anhydrous citric acid used as the carbon source and melamine as the surface passivation for nitrogen source without the use of any acid, alkali, organic solvents or metal ions along with high quantum yield (40% ± 0.06) by solid state method. The emission spectrum shows a strong peak at 440 nm when excited at 360 nm, in the detection only the Hg (II) can readily quench the Photoluminescence (PL) of the N-CDs due to the strong electrostatic interaction and electron transfer between N-CDs and Hg (II), upon the addition of GSH PL of the N-CDs can be recovered owing to the preferred combination of Hg (II) and GSH by forming the Hg (II)-S or Hg (II)-NH bond indicating a remarkably high selectivity towards Hg2+ and biothiols (especially for GSH) among other metals and amino acids with a detection limit as low as 20 nM and 40 nM. With no apparent cytotoxicity, N-CDs could enter the baby hamster kidney (BHK) cells, indicating a practical potential probe for cellular imaging and labeling. Endowed the resulting N-CDs possess excitation dependent PL properties with relatively high sensitivity and selectivity, for the detection of Hg (II) and GSH in aqueous media, environmental and biological sensing applications.