Facile synthesis of cysteine–functionalized graphene quantum dots for a fluorescence probe for mercury ions

Cystenine–functionalized graphene quantum dots (cys–GQDs) were synthesized by a simple and facile method, which involves chemical bond formation between L-cysteine and the graphene quantum dots (GQDs) prepared by the carbonization of citric acid. The obtained cys–GQDs show a strong green fluorescence and a uniform lateral size distribution with high crystallinity. The cys–GQDs are further demonstrated as highly sensitive and selective fluorescence probes for Hg2+. In the Hg2+ detection process, the cys–GQDs shows significant fluorescence quenching through a charge transfer process within the cys–GQDs and Hg2+ complex.