Coumarin-graphene turn-on fluorescent probe for femtomolar level detection of copper(ii)

Herein, a coumarin-graphene based turn-on fluorescence strategy is proposed for the detection of Cu2+ ions. The interaction of graphene with coumarin reduces the luminescence of the latter and together they constitute a sensor unit. The reduced intensity is restored in the presence of Cu2+ ions owing to the greater affinity of the Cu2+ ions to the graphene compared to coumarin. The proposed mechanism was verified by the reduction of the enhanced luminescence when in contact with a strong complexing agent, EDTA. The sensor displays an outstanding sensitivity and selectivity towards Cu2+ ions over other metal ions in aqueous solution. Under optimised conditions, the calibration curve displays a wide linear range (0-20 M) with a limit of detection of 2 femto molar, which is far below the regulatory level, and admirable when compared to other previously reported systems.