A highly selective redox, chromogenic, and fluorescent chemosensor for Hg ²⁺ in aqueous solution based on ferrocene-glycine bioconjugates

The synthesis, electrochemical, optical, and metal-cation-sensing properties of ferrocene-glycine conjugates C 30H 38O 8N 8Fe (2) and C 20H 24O 4N 4Fe (3) have been documented. Both compounds 2 and 3 behave as very selective redox (ΔE 1/2 = 217 mV for 2 and ΔE 1/2 = 160 mV for 3), chromogenic, and fluorescent chemosensors for Hg 2+ cations in an aqueous environment. The considerable changes in their absorption spectra are accompanied by the appearance of a new low-energy peak at 630 nm (2, ε = 1600 M -1 cm -1; 3, ε = 822 M -1 cm -1). This is also accompanied by a strong color change from yellow to purple, which allows a prospective for the "naked eye" detection of Hg 2+ cations. These chemosensors present immense brightness and fluorescence enhancement (chelation-enhanced fluorescence = 91 for 2 and 42 for 3) following Hg 2+ coordination within the limit of detection for Hg 2+ at 7.5 parts per billion. © 2011 American Chemical Society.