An “on–off–on” fluorescent peptide probe for the specific detection of Cu2+ and S2− in living cells and zebrafish

Abstract

Cu²⁺ plays an important role as the third most abundant essential trace element in normal physiological activities and metabolism of organisms. S²⁻ participates in a variety of physiological processes, such as cell apoptosis, intracellular redox balance, insulin secretion and vasodilation. Herein, a novel fluorescent peptide probe P composed of six amino acids and Dansyl chloride dye (Dansyl–Asp–Asp–Gly–Gly–Glu–Glu) has been constructed to detect Cu²⁺ and S²⁻. P can specifically recognize Cu²⁺ without the interference of Hg²⁺ and other metal ions. The mixture of P and Cu²⁺ leads to the formation of a 1 : 1 complex and pronounced fluorescence quenching of the Dansyl-labeled peptide. Molecular simulation has revealed the structural details of the P–Cu complex, indicating that the binding of Cu²⁺ and P is mediated by two coordination sites (O atom of Glu and Asp). The continuous addition of S²⁻ is to recover the fluorescence since it can release the Cu²⁺ from the P–Cu complex. P has been demonstrated as an “on–off–on” biosensor for Cu²⁺ and S²⁻ with the detection limits of 47 nM and 57 nM, respectively. Furthermore, P has been successfully used for the imaging of Cu²⁺ and S²⁻ in the living HeLa cells and zebrafish. The newly developed P has extraordinary features such as good biocompatibility, low biotoxicity, and high specificity of Cu²⁺ and S²⁻, which shows great potential in the studies of various Cu²⁺/S²⁻-involved diseases.