A thiourea-appended rhodamine chemodosimeter for mercury(II) and its bioimaging application.

A rhodamine-thiourea conjugate RTP with an o-phenylenediamine linker was developed as a fluorogenic chemodosimeter for Hg2+ detection. In the presence of Hg2+, a colorless solution of RTP turned pink with a maximum absorption band at 555nm and with a 62-fold fluorescence enhancement at 578nm (Φ=0.34). RTP is highly selective to Hg2+ among other metal ions with a detection limit of 1.6nM (0.3ppb). A similar rhodamine analog with a flexible ethylenediamine spacer was less selective and less sensitive than RTP. Hg2+ induced cyclic guanylation to yield a benzimidazole moiety and a subsequent ring-opening of the spirolactam unit resulted in chromogenic and fluorogenic changes. The membrane-permeable RTP probe was successfully demonstrated in monitoring of Hg2+ in cultured HeLa cells.