A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ 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 micromol L(-1) with a detection limit of 8.5 x 10(-10) mol L(-1) (3sigma). 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.