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 Cu2+ with significant fluorescent "turn-off" response, with a visible colorimetric change from yellow to orange. The combination ratio of FLH to Cu2+ (1:1) was determined using ESI-HRMS spectra and Job's plot. The fluorescent emission showed a good linear response (R2 = 0.9986) with a low detection limit of 1.5 nM. In addition, the FLH-Cu2+ 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 Cu2+ 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 Cu2+ and CN- in living cells through fluorescence imaging.