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

Abstract A rhodamine-thiourea conjugate RTP with an o -phenylenediamine linker was developed as a fluorogenic chemodosimeter for Hg 2+ detection. In the presence of Hg 2+ , a colorless solution of RTP turned pink with a maximum absorption band at 555 nm and with a 62-fold fluorescence enhancement at 578 nm (Φ = 0.34). RTP is highly selective to Hg 2+ among other metal ions with a detection limit of 1.6 nM (0.3 ppb). A similar rhodamine analog with a flexible ethylenediamine spacer was less selective and less sensitive than RTP . Hg 2+ 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 Hg 2+ in cultured HeLa cells.