Synthesis and NMR-Spectroscopic Investigation of Peptide-Coated Ultrasmall Gold Nanoparticles (1-2 nm)

Ultrasmall gold nanoparticles (diameter 1-2 nm) have become increasingly important in biomedicine in recent years. If they are functionalized with biomolecules, they can be used in cancer therapy or for targeted drug release. The nature and size of the biomolecule determined the interaction with the gold surface and the number of attached ligands, including their molecular footprint.<br/>We have attached cysteine-terminated peptides of variable length to ultrasmall gold nanoparticles. Besides model peptides consisting of a terminal cysteine and a chain of alanine, bioactive peptides were attached. The nanoparticle size was determined by differential centrifugal sedimentation (DCS), diffusion ordered NMR spectroscopy (DOSY), and transmission electron microscopy (TEM). By taking advantage of the fact that NMR spectroscopy is possible for ultrasmall nanoparticles, we have extensively characterized the ligand shell on the nanoparticles, including the binding state, by NMR spectroscopy. We have also determined the number of ligands on each nanoparticle by NMR spectroscopy and determined the change of molecular footprint as a function of peptide size. The ligand exchange studies at different temperature and pH as followed by NMR indicated the stability of the nanoparticle-peptide assembly which is important for its biomedical application.