Development and applications of two colorimetric and fluorescent indicators for Hg2+ detection

Two rhodamine-active probes RBAI (Rhodamine B-di-Aminobenzene-phenyl Isothiocyanate) and RGAI (Rhodamine 6G-di-Aminobenzene-phenyl Isothiocyanate) were designed, synthesized and characterized. The probes were developed as fluorescent and colorimetric chemodosimeters in ethanol-water solution with a broad pH span (5-10) and high selectivity toward Hg2+ but no significant response toward other common competitive cations. The Hg2+-promoted ring opening of spirolactam of the rhodamine moiety induced cyclic guanylation of the thiourea moiety, which resulted in the dual chromo- and fluorogenic observation (off-on). Cytotoxicity and bioimaging studies by L929 living cells and living mice indicated that the probes were negligible cytotoxicity, cell permeable and suitable for detecting Hg2+ in biological environments. Moreover, the new probes not only displayed excellent abilities for the successful detection of Hg2+ in L929 living cells and living mice but also able to detect Hg2+ by adsorbing on solid surfaces and quantitative detection of Hg2+ in real water samples with good recovery (more than 90%), indicating that they have promising prospect for application for Hg2+ sensing in environmental and biological sciences.