Gram-scale synthesis of nitrogen doped graphene quantum dots for sensitive detection of mercury ions and l-cysteine

Sensitive and reliable detection of mercury ions (Hg(2+)) and l-cysteine (l-Cys) is of great significance for toxicology assessment, environmental protection, food analysis and human health. Herein, we present gram-scale synthesis of nitrogen doped graphene quantum dots (N-GQDs) for sensitive detection of Hg(2+) and l-Cys. The N-GQDs are one-step synthesized using bottom-up molecular fusion in a hydrothermal process with gram-scale yield at a single run. N-GQDs exhibit good structural characteristics including uniform size (∼2.1 nm), high crystallinity, and single-layered graphene thickness. Successful doping of N atom enables bright blue fluorescence (absolute photoluminescence quantum yield of 24.8%) and provides unique selectivity towards Hg(2+). Based on the fluorescence quenching by Hg(2+) (turn-off mode), N-GQDs are able to serve as an effective fluorescent probe for sensitive detection of Hg(2+) with low limit of detection (19 nM). As l-Cys could recover the fluorescence of N-GQDs quenched by Hg(2+), fluorescent detection of l-Cys is also demonstrated using turn-off-on mode.