Hit Multiple Targets with One Arrow: Pb2+ and ClO- Detection by Edge Functionalized Graphene Quantum Dots and Their Applications in Living Cells

Recently, multimodal detection of analytes through a single nanoprobe has become an eminent approach for researchers. Herein a fluorescent nanoprobe, functionalized-GQD (F-GQD), has been designed through edge functionalization of graphene quantum dots (GQDs) by 2,6-diaminopyridine molecules. The fluorescence of F-GQD is quite sensitive to medium pH, making it a suitable pH sensor within the pH range 2-6. Interestingly, F-GQD shows dual sensing of Pb2+ and ClO- by entirely different pathways; Pb2+ exhibits fluorescence turn-on performance while ClO- triggers turn-off fluorescence quenching. The fluorescence enhancement may originate from the Pb2+-induced aggregation of the nanodots. The limit of detection (LOD) was also impressive, 1.2 mu M and 12.6 nM for Pb2+ and ClO-, respectively. The detailed mechanistic investigations reveal that both dynamic and static quenching effects operate together in the F-GQD-ClO- system. The dynamic quenching was attributed to the energy migration from F-GQD to ClO- through hydrogen bonding interaction (static quenching) between the amine group at the F-GQD surface and ClO-. The F-GQD nanodot reveals excellent sensitivity toward the detection of ClO- in real samples. Moreover, the F-GQDs also serve as multicolor fluorescent probes for cell imaging; the probe can easily penetrate the cell membrane and successfully detect intracellular ClO-.