Dual optical Hg2+-selective sensing through FRET system of fluorescein and rhodamine B fluorophores

A “naked-eye” indicator and fluorescent chemosensor based on fluorescein connected to two rhodamine B fluorophores by hydrazide moieties, RF1, was designed and synthesized for highly sensitive and selective detection of Hg2+. The sensor system operated through the FRET process from the fluorescein energy donor to the ring-opened rhodamine B acceptors. The binding to Hg2+ was observed through both fluorescence enhancement and a chromogenic change (from colorless to pink). The sensor is shown to discriminate various foreign metal ions, particularly Ag+, Pb2+ and Cu2+, as well as Li+, Na+, Mg2+, Cd2+, K+, Al3+, Fe3+, Ca2+, Ba2+ and Zn2+, with a detection limit of 2.02 × 10−8 M or 4 ppb toward Hg2+.