A peptide-based multifunctional fluorescent probe for Cu2+, Hg2+ and biothiols

Abstract

A peptide-based fluorescent probe (Dansyl-His-Pro-Gly-Trp-NH₂, D-P4) bearing the dansyl fluorophore and tryptophan residue has been developed for the detection of Hg²⁺, Cu²⁺ and biothiols (–SH). DP-4 exhibited high selectivity and sensitivity for Cu²⁺ and Hg²⁺ in the presence of 17 metal ions and 6 anions. D-P4 could differentiate Hg²⁺ and Cu²⁺via a ratiometric response toward Hg²⁺ and quenching response toward Cu²⁺. Upon the addition of Hg²⁺ or Cu²⁺ ions, the D-P4 solution displayed a colour change, which was visible to the naked eyes under a UV lamp. The limits of detection (LOD) of DP-4 are 37 nM for Hg²⁺ and 105 nM for Cu²⁺, which for Cu²⁺ is much lower than the EPA drinking water maximum contaminant level. Additionally, the binding stoichiometry, binding affinity and pH influence of D-P4 for Hg²⁺ and Cu²⁺ ions were studied. Determination of Hg²⁺ and Cu²⁺ in river water samples with D-P4 showed satisfactory results. It is noteworthy that the D-P4-Hg system could be regenerated using cysteine (Cys), which was confirmed via circular dichroism (CD) and UV-vis absorption spectroscopy. Moreover, the D-P4-Hg system could be used to detect cysteine, homocysteine (Hcy) and glutathione (GSH). These results indicate that the D-P4-Hg system can selectively detect cysteine among the 20 common amino acids with an LOD of 82 nM.