Mercury ion is one of the most toxic and dangerous heavy metal elements. And it would induce permanent harm to brain, bone, kidney, central nervous system, immune system and endocrine system. Mercury and mercury-contaminating material are widespread through various routes, e.g. volcanic eruption, mining and solid waste incineration, resulting in vast amounts of water, air and soil are contaminated. Subsequent bioaccumulation through the food chain can lead to severe damages to people's health. Thus sensitive detection of Hg2+ in environmental samples and corresponding study on biology become one of the hottest topics recently.
Although there are many detection methods for metal ions, such as atomic absorption and electron paramagnetic resonance, these methods are not suitable for direct and on-site detection of metal ions in biological body, and pretreatment of sample is complex as well, thus their applications are limited. On the other hand, the method based on fluorescent probe attracts much attention due to its high sensitivity, good selectivity, quick respond and suitability for on-site detection. However, among most of fluorescent probes for Hg2+ detection on the basis of coordination mechanism like PET and ICT, the one having good properties and suitable for detecting Hg2+ in low level is little. Since Hg2+ could quench fluorescence because of its heavy atom effect, and Pb2+, Zn2+ and Ag+ usually disturb the detection of Hg2+, a new kind of probe based on ion-selective reaction is developed to avoid low sensitivity and low selectivity of the fluorescent probe based on coordination mechanism mentioned above.
Up to now, thioether fluorescence probe and desulfurization fluorescence probe are main examples of probes selective for Hg2+, but there are also some deficiencies in their performance. For the fluorescence probe based on thioether-Hg2+ coordination, the binding ability of thioether to Hg2+ is not very strong which impedes the application for detecting low-concentration Hg2+ in physiological environment (Knut Rurack, Ute Resch-Genger, Monika Spieles and Julia L. Bricks, Chem. Commun., 2000, 2103-2104). Desulfurization fluorescence probe is developed in the recent years, which exhibits many advantages such as pH insensitivity and large fluorescence enhancement. However, sometimes high temperature is needed to promote the desulfurization with a vast of Hg2+, and in addition this detection may be disturbed by Ag+ and Pb2+ (Mi Young Chae and Anthony W. Czarnik, J. Am. Chem. Soc. 1992, 114, 9704-9705; Song, K. C., Kim, J. S., Park, S. M., Chung, K.-C., Ahn, S, and Chang, S.-K. Org. Lett. 2006, 8, 3413-3416).