Peptide-based colorimetric and fluorescent dual-functional probe for sequential detection of copper(Ⅱ) and cyanide ions and its application in real water samples, test strips and living cells.

A novel dual-functional peptide probe FLH based on fluorescent "on-off-on" strategy and colorimetric visualization method was designed and synthesized. This new probe exhibited highly selective and rapid detection of Cu with significant fluorescent "turn-off" response, with a visible colorimetric change from yellow to orange. The combination ratio of FLH to Cu (1:1) was determined using ESI-HRMS spectra and Job's plot. The fluorescent emission showed a good linear response (R = 0.9986) with a low detection limit of 1.5 nM. In addition, the FLH-Cu complex displayed colorimetric changes and a fluorescent "off-on" response toward CN over a wide pH range from 7 to 12. This detection behavior was observed within 20 s, with a limit of detection (LOD) for CN at 12.7 nM. Based on stability and accuracy, FLH was next developed as dual-functional test strips, and was also successfully applied to detect Cu and CN in two actual water samples. More importantly, the cytotoxicity studies indicated that FLH had good biocompatibility and low toxicity, and was successfully utilized for monitoring Cu and CN in living cells through fluorescence imaging.