Development of ratiometric fluorescent probes based on peptides for sensing Pb in aquatic environments and human serum.

The detection of Pb ions in aquatic environments and biofluid samples is crucial for assessment of human health. Herein, we synthesized two fluorescent probes (1 and 2) consisting of the peptide receptor for Pb and a benzothiazolyl-cyanovinylene fluorophore that exhibited excimer-like emission when it aggregated. The peptide-based probes sensitively detected Pb in purely aqueous solution (1% DMF) through ratiometric fluorescent response with a decrease in monomer emission at 520 nm and an increase in excimer emission at 570 nm. Specially, probe 2 showed remarkable detection features such as high selectivity for Pbover 15 metal ions, high binding affinity (K = 5.83 × 10 M) for Pb, significant emission intensity changes, low detection limit (3.8 nM) of Pb, high water solubility, and visible light excitation (450 nm). Probe 2 was successfully used to quantify nanomolar concentration (0 ∼ 800 nM) of Pb in real water samples (ground water and tap water). Specially, 2 was successfully applied for the quantification of Pb in human serum by combination of microwave-assisted human serum digestion and filtration of digested serum by anion exchange cartridge. We clearly investigated the binding mode of 2 with Pb using H NMR, IR spectroscopy, pH titration, confocal microscopy, and size analysis. The peptide-based fluorescent probe might have great application potential for sensing Pb in aquatic environments and biofluid samples.