Phenanthroline bridged bis(beta-cyclodextrin)s/adamantane-carboxylic acid supramolecular complex as an efficient fluorescence sensor to Zn2+

A water-soluble fluorescent Zn2+ sensor, 1,10-phenanthroline bridged bis(beta-cyclodextrin) (1), was synthesized by click chemistry, and its fluorescence sensing behavior toward Zn2+ against various metal ions was investigated under physiological conditions. Significantly, 1 showed high selectivity and sensitivity toward Zn2+ with a limit of detection (LOD) down to 10(-7) M. Moreover, the spectrophotometric studies demonstrated that after complexation with 1-admantanecarboxylic acid sodium salt (AdCA), the 1/AdCA complex gave much stronger binding affinity and lower LOD value toward Zn2+ through a cyclodextrin/substrate/Zn2+ triple recognition mode. The fluorescence stopped-flow experiments also indicated that the association rate of complex 1/AdCA to Zn2+ was much faster than compound 1 to the same ion. Furthermore, the fluorescence intensity of 1 and 1/AdCA was greatly enhanced after binding Zn2+ in living cells, and thus 1 and complex 1/AdCA could be considered as a biosensor for Zn2+ at the cellular level.