Peptide-based colorimetric and fluorescent dual-functional probe for sequential detection of copper(â ¡) 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.

A bifunctional peptide-based fluorescent probe for ratiometric and "turn-on" detection of Zn(II) ions and its application in living cells.

In this work, a bifunctional peptide-based fluorescent probe L containing a tetrapeptide scaffold (Pro-Gly-His-Trp-NH2) and a dansyl group was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, L, based on a FRET mechanism, exhibited high selectivity, excellent ratiometric signals, and fast response to Zn2+ in aqueous solutions at an excitation wavelength of 280 nm. In addition, when excited at 320 nm, L exhibited a fluorescent "turn-on" response towards Zn2+ based on PET mechanism. More importantly, the stoichiometry of L and Zn2+ was determined to be 2:1 by fluorescent titration, Job's plot method, and ESI-MS spectrometry. The association constant for Zn2+ ions was determined to be 6.26 × 108 M-2, while the limit of detection (LOD) of L was estimated as 5.43 nM, which is a much lower value than WHO and EPA guidelines for drinking water. Moreover, L was successfully applied to detect both Zn2+ and Cu2+ in living cells due to good biocompatibility and excellent low toxicity.

A novel peptide-based fluorescent probe with a large stokes shift for rapid and sequential detection of Cu2+ and CN- in aqueous systems and live cells.

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.