A dual-functional colorimetric and fluorescent peptide-based probe for sequential detection of Cu and S in 100% aqueous buffered solutions and living cells.

Highly sensitive and selectivite detection of copper ions (Cu) and hydrogen sulfide (HS) 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 Cu and S based on colorimetric and fluorescent methods. The new probe L displayed excellent "turn off" fluorescence response and good selectivity for Cu 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 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 (Cu) and 27.2 nM (S), which were well below U.S. EPA safety levels. In addition, L could be cycled to alternately detect Cu and S, thereby making it a promising reversible probe. Moreover, L was successfully applied to monitoring Cu and S in live RKO cells through fluorescence imaging, exhibiting low cytotoxicity and good cell permeability.