Reduced Graphene Oxide–Thioguanine Composites for the Selective Detection of Inorganic and Organic Mercury in Aqueous Media

Graphene oxide (GO) and its reduced form reduced GO (rGO) have received huge research attention because of their unique surface properties and diverse application potential. Here, a rGO-based turn-on fluorimetric sensing platform for the label-free detection and subsequent discrimination of inorganic and organic mercurials was developed by utilizing the inherent fluorescence property of rGO. 6-Thioguanine (6-TG) was used as a fluorescence quencher, and the corresponding nonfluorescent rGO–6-TG ensemble was utilized to detect Hg(II) ions by an affinity-based complexation and decomplexation phenomenon. The rGO–6-TG ensemble interacts with Hg(II) ions with high selectivity owing to the strong affinity of Hg(II) toward the thiol group of 6-TG to result in a strong blue fluorescence. Limits of detection of inorganic and organic mercury were determined as 0.8 and 1.72 μM, respectively. Discrimination of inorganic mercury from organic mercury was achieved by simple introduction of iodide ions, which immediately drive inorganic Hg(II) out of the solution (from the rGO–6-TG–Hg–6-TG complex) by forming HgI2 (Ksp > 10–29). The rGO–6-TG–Hg–6-TG ensemble was successfully utilized for the detection of iodide ions making it a dual sensor for Hg(II) and I–. Simple, noncovalent modification and ability to discriminate organic mercury from inorganic mercury are few key features of this rGO-based sensing platform.