Graphene quantum dots as a fluorescent sensing platform for highly efficient detection of copper(II) ions

Graphene quantum dots (GQDs) have been attractive due to their optical properties with the change of the size. The stable blue fluorescent GQDs are prepared via the hydrothermal method using reoxidized graphene oxide. Based on the quenching of as-prepared GQDs fluorescence by Cu(II) in water, a facile and direct fluorescence sensor for the detection of Cu2+ ions has been studied. It exhibits an extraordinarily high sensitivity and selectivity to Cu2+ ions compared to other metal ions in aqueous solution. The fluorescence intensity is inversely proportional to the concentration of Cu2+ ions, and the calibration curve displays linear regions over the range of 0-15 μM, with a detection limit of 0.226 μM. These results indicate that GQDs, as a fluorescent sensing platform, could meet the selective requirements for biomedical and environmental application and be sensitive enough to detect Cu2+ ions in environmental water samples, even in drinking water, which has a limit of 20 μM defined by the U.S. Environmental Protection Agency. The possible mechanism of Cu(II)-induced fluorescence quenching of GQDs was also discussed. The fluorescence lifetime experimental result demonstrates that the quenching mechanism appears to be predominantly of the static (rather than dynamic) type.