Graphene quantum dots as effective probes for label-free fluorescence detection of dopamine

A label-free fluorescence based method using graphene quantum dots (GQDs) as effective probes was developed for sensitive and selective detection of dopamine (DA). The initial strong blue fluorescence of the GQDs in aqueous solution was effectively quenched upon addition of DA. The quenching mechanism may involve transfer of electrons from the photoexcited GQDs to dopamine-quinine, which was produced via the oxidization of DA by ambient O2 in alkaline solution. The quenching efficiency was linearly proportional to the concentration of DA within the range of 0.25-50 μM with a low detection limit down of 0.09 μM. The proposed sensing system is simple and low-cost with facile experimental operations, and has a high selectivity for DA over a number of possible interfering species. Additionally, this method was successfully applied to the determination of DA in biological samples with satisfactory recoveries (98.8-106.4%).