A fluorescent probe based on visible light-emitting functionalized Graphene Quantum dots for the sensitive and selective detection of Pb (II) ions

We demonstrate a functionalization strategy to improve the basic fluorescence properties and to systematically customize the bandgap properties of Graphene quantum dots (GQD) by functionalization with a well-known fluorophore called Dithienopyrrole derivative (DTPAN) whereby making them adequately acceptable for the suitable promising applications. We observed that the functionalization with DTPAN not only shifts the photoluminescence spectrum but also enhances the other inherent fluorescence properties. The functionalized material (DTPAN-fn-GQD) is used for the sensitive detection of Pb²⁺ ions in aqueous media. The detection of Pb²⁺ within the linear range of 0.5–40 nM was obtained with a limit of detection of 0.25 nM. Stern–Volmer analysis suggests that both static and dynamic mechanisms are active for the quenching process and further the Cyclic Voltammetry measurements along with DFT calculations of DTPAN-fn-GQD recommend the possibility of electron transfer from the HOMO of DTPAN to the LUMO of GQD upon photoexcitation. However, the presence of Pb²⁺ metal ions will perturbate this charge transfer process and lead to quenching of fluorescence. The sensor was applied efficiently to the determination of Pb²⁺ ions in real water samples. Paper strips based on the developed fluorescent probe were shown to be useful for rapid visual sensing, which can expand its potential ability for developing simple analytical devices.