Isocyanonaphthalenes as extremely low molecular weight, selective, ratiometric fluorescent probes for Mercury(II)

The specially designed chemical structure of our recently developed solvatochromic amino-isocyanonaphthalene (ICAN) dye family enables the selective detection of Hg²⁺ and at the same time is able to indicate the presence of Ag⁺. In addition to its easy preparation and nontoxic nature, ICAN is the lowest molecular weight dye reported for ratiometric fluorescent Hg²⁺ detection in water, so far. The basis of this double selectivity is the reduction of the isonitrile moiety to amine by a chemical reaction with Hg²⁺ resulting in a greater than 100 nm hypsochromic shift (and switch on of fluorescence) of the emission maximum relative to ICAN, whereas the complexation of Ag⁺ with the NC group yields an approximately 20 nm bathochromic shift (and quenching). In contrast, other common ions have little effect on the position of the emission maximum in aqueous medium. In completely aqueous medium at pH = 6, the limit of quantification was found to be lower than 17 nM and the limit of detection lower than 6 nM for Hg²⁺. The practical applicability of the method was demonstrated on dental amalgam.