Bioinspired Systems for Metal-Ion Sensing: New Emissive Peptide Probes Based on Benzo[d]oxazole Derivatives and Their Gold and Silica Nanoparticles

Seven new bioinspired chemosensors (24 and 710) based on fluorescent peptides were synthesized and characterized by elemental analysis, 1H and 13C NMR, melting point, matrix-assisted laser desorptionionization time-of-flight mass spectrometry (MALDI-TOF-MS), and IR and UVvis absorption and emission spectroscopy. The interaction with transition- and post-transition-metal ions (Cu2+, Ni2+, Ag+ , Zn2+, Cd2+, Hg2+, Pb2+, and Fe3+) has been explored by absorption and fluorescence emission spectroscopy and MALDI- TOF-MS. The reported fluorescent peptide systems, introducing biological molecules in the skeleton of the probes, enhance their sensitivity and confer them strong potential for applications in biological fields. Gold and silica nanoparticles functionalized with these peptides were also obtained. All nanoparticles were characterized by dynamic light scattering, transmission electron microscopy, and UVvis absorption and fluorescence spectroscopy. Stable gold nanoparticles (diameter 210 nm) bearing ligands 1 and 4 were obtained by common reductive synthesis. Commercial silica nanoparticles were decorated at their surface using compounds 810, linked through a silane spacer. The same chemosensors were also taken into aqueous solutions through their dispersion in the outer layer of silica core/poly(ethylene glycol) shell nanoparticles. In both cases, these complex nanoarchitectures behaved as new sensitive materials for Ag+ and Hg2+ in water. The possibility of using these species in this solvent is particularly valuable because the impact on human health of heavy- and transition-metal-ion pollution is very severe, and all analytical and diagnostics investigations involve a water environment.