Electrochemical synthesis of multicolor fluorescent N-doped graphene quantum dots as a ferric ion sensor and their application in bioimaging.

A novel electrochemical strategy for simple and facile synthesis of semicarbazide functionalized nitrogen-doped graphene quantum dots (N-GQDs) was reported, based on direct exfoliation and oxidation from graphite rods. The average diameter of the as-synthesized N-GQDs is about 20 nm, and their dispersion is bright yellow due to the rich nitrogen and oxygen functional groups on their surface. The N-GQD dispersion was further applied in the selective detection of ferric ions (Fe) based on the photoluminescence (PL) quenching of N-GQDs after adding Fe. The fluorescent sensor has a wide linear range of 0-200 μM and a detection limit of 0.87 μM, which is much lower than the maximum level (0.3 mg L, equivalent to 5.4 μM) of Fe permitted in drinking water by the U.S. Environmental Protection Agency (EPA). Moreover, these novel N-GQDs exhibit much wider emission bands, which extend into the entire visible region, and emit three primary color fluorescence independently. This distinctive behavior of the as-prepared GQDs not only breaks the limitation that traditional reported GQDs only exhibit blue emission in the short-wavelength region, but may also provide a new research platform for further applications of GQDs in real environmental detection and biological imaging systems.