Graphene-dye supramolecular assembly for parts per trillion level F− monitoring

Abstract

An innovative and simple displacement approach based on Graphene and Rhodamine supramolecular assembly that could sense fluoride ion in aqueous solution is demonstrated. Graphene-Rhodamine unit engages in the formation of a supramolecular complex between Rhodamine (indicator) and Graphene (receptor), followed by the displacement of the indicator with the advent of F− ion. These changes alter optical characteristics of the supramolecular entity which can be quantified using spectroscopic techniques. The findings of UV–vis and Photoluminescence analysis together with the life-time measurement studies reveal that through the interactions of Graphene sheets with Rhodamine dye quenches the optical response of the dye which can be selectively restored by introducing traces of F−. The detection limit was found to be 11 ppb and 850 ppt by UV–vis and Photoluminescence studies respectively, falling admirably below the permissible F- level in drinking water i.e. 1.5 ppm. The proof of concept for this sensing strategy is demonstrated through paper-based testing strips that can function as a portable layman’s tool for sub ppb level detection of the test anion. Investigations on real water samples spiked with Fluoride ion assures that the proposed sensor moiety can swiftly monitor the test ion levels in complex samples and affirm the utility of the system for practical applications.