A novel peptide-based fluorescent probe with a large stokes shift for rapid and sequential detection of Cu²⁺ and CN^-...

A novel fluorescent probe (DSD) was reasonably designed and synthesized with dansyl-labeled dipeptide (Dan-Ser-Asp-NH₂). DSD featured remarkably large Stokes shift (230 nm) and perfect water solubility, and exhibited high selectivity and rapid recognition toward Cu²⁺via fluorescence quenching. The detection limit of DSD for Cu²⁺ was 2.4 nM, indicated that DSD has excellent sensitivity. In addition, the stoichiometry between DSD and Cu²⁺ were detected as 1:1 by fluorescence titration, Job's plot and ESI-HRMS data. As designed, DSD-Cu²⁺ system was able to sequentially detect CN^- according to the displacement approach with fluorescence "off-on" response, and the detection limit for CN^- was calculated to be 41.9 nM. Specifically, the response time of DSD with Cu²⁺ and CN^- was less than 40 s, which rendered it suitable for real time detection in actual water samples. In addition, with the alternate addition of Cu²⁺ and CN^-, the reversible cycles could be repeated for at least 10 times, indicated that DSD was a promising reversibility probe. DSD showed low toxicity and good biocompatibility, and was successfully applied to detect Cu²⁺ and CN^- in living cells.