A rhodamine-based Hg2+-selective fluorescent probe in aqueous solution

A new rhodamine-based Hg2+-selective fluorescent probe (I) was designed and synthesized. Compound I displays excellent selective and sensitive response to Hg2+ over other transition metal ions in neutral aqueous solutions. I itself is a colorless, nonfluorescent compound. Upon addition of Hg2+ to its solution, the thiosemicarbazide moiety of I undergoes an irreversible desulfurization reaction to form the corresponding 1,3,4-oxadiazole (II), a colorful and fluorescent product, causing instantaneous development of visible color and strong fluorescence emission. Based on this mechanism, a fluorogenic probe for Hg2+ was developed. The fluorescence increases linearly with the Hg2+ concentration up to 0.8 mu mol L-1 with the detection limit of 9.4 nmol L- (3 sigma).