A novel fluorescent probe based on rhodamine B derivative for highly selective and sensitive detection of mercury(II) ion in aqueous solution

In the present work, a new rhodamine B Schiff base 3′,6′-bis(diethylamino)-2-(2-oxoethylideneamino)-spiro[isoindoline-1,9′-xanithen]-3-one (RHO) was designed and easily prepared as a Hg2+ fluorescent and colorimetric probe, which could selectively and sensitively detect Hg2+ in 7:3 (v/v) ethanol–water solution by showing enhanced fluorescence emission. Meanwhile distinct color change from colorless to pink also provided “naked eye” detection of Hg2+ owing to the ring opening of spirolactam of the rhodamine derivative. Other ions including alkali and alkaline earth metal ions (K+, Mg2+, and Ca2+), and some transition metal ions (Ni2+, Co2+, Fe2+, Cu2+, Zn2+, Cd2+, Ag+, Pb2+, Cr3+, and Fe3+) could hardly induce any interference. For further use in practical applications in optical ion sensing devices, we immobilized the probe onto silica spheres to explore its functionality in inorganic and organic hybrid materials. As a result, excellent discrimination of Hg2+ from other cations could also be obtained.