A simple fluorescent "on-off-on" nanosensor based on nitrogen-doped carbon dots for selective detection of Hg 2+and thiamine

A fluorescent "on -off -on" nanosensor based on nitrogen -doped carbon dots (N -CDs) was developed for the detection of Hg 2 + and thiamine (vitamin B1). N -CDs were synthesized through a one-step microwave heating approach using D -fructose and L -lysine as precursors in aqueous media. The as -synthesized N -CDs exhibited a strong fluorescent emission peak at 440 nm when excited at 360 nm. The fluorescence emission intensity of synthesized N -CDs was quenched when adding Hg 2 + (turn off) at concentrations between 1 and 10 mu M, with limit of detection (LOD) 0.40 mu M due to the formation of a complex between N -CDs and Hg 2 + . By contrast, quenched fluorescence of the N-CD/Hg 2 + system was recovered by adding thiamine that effectively removed Hg 2 + from the N -CD surface resulting in fluorescence turning on. The intensity of the restored fluorescence was proportional to the concentration of thiamine, ranging from 0.2 to 2.0 mu M with LOD down to 30 nM. The "on -off -on" process of N -CD fluorescence probes was successfully applied to determine Hg 2 + in real water and cosmetic samples and thiamine in grain food samples with accurate results.