A novel fluorescent and colorimetric dual-signals peptide-based probe for sequential recognition of Cu(II) and cimetidine and its multi-functional applications

A novel dual-signals peptide-based probe FDKSH was designed and synthesized based on 5-carboxy fluorescein (5-FAM) labelled tetrapeptide backbone (Asp-Lys-Ser-His-NH2). FDKSH exhibited a highly selective fluorescence "on-off" response and obvious colorimetric recognition to Cu2+ in 10 mM HEPES buffer solution at pH 7.4. Meanwhile, the limit of detection (LOD) was found to be 62.1 nM, which was much lower than that of stated by World Health Organization (WHO) in drinking water (30.0 μM). As a new promising cascade probe, the Cu(II)-assisted peptide ensemble probe (FDKSH-Cu2+ ensemble) has very high selectivity for cimetidine by the displacement method with LOD of 63.5 nM. In addition, FDKSH was successfully used to determine Cu2+ and cimetidine in two actual water samples. Additionally, FDKSH was also successfully used for monitoring Cu2+ and cimetidine in living cells and zebrafish, and showed low toxicity and excellent fluorescence imaging performance. It is worth noting that FDKSH-impregnated test strips exhibited significant fluorescence and colorimetric color changes for Cu2+ and cimetidine directly observed by naked eye. What's more, smartphone with RGB color recognition function provided a new method for semi-quantitative visual detection of Cu2+ and cimetidine by analyzing different concentrations of Cu2+ and cimetidine without expensive instruments.