Dansyl-peptide dual-functional fluorescent chemosensor for Hg2+ and biothiols

A new dansyl-peptide dual-functional fluorescent chemosensor (D-ECEW-NH2, D-P4) was developed via Fmoc solid phase peptide synthesis (SPPS), which displayed an excellent selectivity and high sensitivity for Hg2+ by turn on response in 10 mM 2-[4-(2-Hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) solution (pH 7.1). The sensing mechanism for Hg2+ is by two pathways, one is fluorescence resonance energy transfer (FRET) effect between tryptophan (donor) and dansyl (acceptor) fluorophores due to the interaction of Hg2+ ion with D-P4 evidenced by fluorescence excitation spectra at 290 nm, while the other is the chelation enhanced fluorescence (CHEF) effect evidenced by fluorescence excitation spectra at 330 nm. D-P4 sensor was used to detect Hg2+ with low detection limit of 23.0 nM. Furthermore, the binding stoichiometry and binding constant, as well as pH influence of D-P4 for Hg2+ were investigated. Surprising but interestingly, D-P4-Hg system has been found a significant fluorescence enhancement response toward biothiols including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), which can be used for the detection of biothiols. Its detection limit for Cys was 52.0 nM.