Highly selective peptide-based fluorescent turn-on probe with large Stokes shift for the detection of Cd(II) and its applications in bio-imaging and smartphone-assisted recognition

Abstract

Cadmium ions (Cd2+) is a ubiquitous environmental pollutant that endangers all forms of life, and it has become critical to develop simple and highly selective detection methods for monitoring Cd2+. Herein, a new fluorescent turn-on probe DPGC with dansyl fluorophore labelled tripeptide (ProGlyCys-NH2) was successfully synthesized using solid-phase peptide synthesis technology with Fmoc chemistry. Interestingly, DPGC showed high specificity and fluorescence “turn on” response towards Cd2+ in 100% aqueous solution. In addition, the limit of detection (LOD) for Cd2+ recognition by DPGC was calculated to be 12.4 nM. The pH test showed that DPGC had a wide detection range of 7–11 for Cd2+, and the response time was also less than 30 s. Notably, the DPGC-Cd2+ complex forms a 2:1 binding stoichiometry was determined using fluorescence titration, Job's plot, ESI-HRMS and DFT calculations. Additionally, the binding of DPGC with Cd2+ was found fluorescence reversible on addition of EDTA. Meanwhile, DPGC has excellent membrane permeability and low cytotoxicity, and was successfully employed for detecting Cd2+in living cells and zebrafish. More importantly, the colour change of Cd2+ solution with different concentrations under 365 nm UV light was detected by a smartphone App to achieve semi-quantitative visual analysis of Cd2+ ions.