A dual-functional colorimetric and fluorescent peptide-based probe for sequential detection of Cu²⁺ and S^2- in 100%...

Highly sensitive and selectivite detection of copper ions (Cu²⁺) and hydrogen sulfide (H₂S) have become important research topics due to the potential harmful impacts of these chemicals to human health and the environment. In this study, we report the synthesis of a dual-functional peptide-based probe L (FITC-AhxSerSerHis), designed to mimic a copper-sulfur metalloprotein, and capable of continuous detection of Cu²⁺ and S^2- based on colorimetric and fluorescent methods. The new probe L displayed excellent "turn off" fluorescence response and good selectivity for Cu²⁺ ions via a modification of the tripeptide and fluorescein isothiocyanate group, and produced an obvious color change visible to the naked eye. Furthermore, as an excitable probe, the L-Cu complex could continuously detect S^2- with high selectivity and sensitivity in 100% aqueous buffered solutions. The detection limits for fluorescence titration measurements, calculated using the equation 3σ/k, were 76.7 nM (Cu²⁺) and 27.2 nM (S^2-), which were well below U.S. EPA safety levels. In addition, L could be cycled to alternately detect Cu²⁺ and S^2-, thereby making it a promising reversible probe. Moreover, L was successfully applied to monitoring Cu²⁺ and S^2- in live RKO cells through fluorescence imaging, exhibiting low cytotoxicity and good cell permeability.