A highly selective and sensitive fluorescein-based chemodosimeter for Hg^2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg^2+ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg^2+ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg^2+ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500–600 nm. Based on the above mechanism, a fluorogenic Hg^2+-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg^2+ concentration up to 1.0 (mu)mol L^-1 with a detection limit of 8.5 × 10^-10 mol L^-1 (3(sigma)). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg^2+. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg^2+ concentrations in realistic media.