Visible study of mercuric ion and its conjugate in living cells of mammals and plants.

The investigation of mercuric ion and mercuric conjugate inside live specimens has drawn intense attention because of their cytotoxicity. The translocation, transportation, and distribution of Hg2+ inside either mammals or plants, however, are still invisible due to the lack of favorable fluorescent molecular sensors for Hg2+. Here, two sensors, 2,6-bis(4'-peperazino-N'-hydroxylethoxylethylene-1',8'-naphthalimide)dimethylpyridine and 2,6-bis(4'-peperazino-N'-butyl-1',8'-naphthalimide)dimethylpyridine, which were composed of nitrogen atoms of 2,6-bis(aminomethyl)pyridine as the ion receptor and the donor of photoinduced electron transfer, were applied to the cultured mammalian cells and plant cells. Their membrane permeability, low toxicity, slow bleaching/fading, and high selectivity and sensitivity to Hg2+ in a live cell rendered them attractive to become real-time and real-space sensors. For the first time, the transportation of Hg2+ cation and Hg2+ conjugate of cysteine was observed with the help of a fluorescence microscope. The chloroplast location of Hg2+ in transgenic tobacco was also visible.