Biofunctionalization of Plasmonic Nanoparticles with Short Peptides Monitored by SERS.

In order for plasmonic nanoparticles to be usable in biomedical applications their surface requires functionalization with biocompatible material. For this purpose short peptides, CFY, CFFY, CLY, were designed and replacement of the capping agent poly(vinylpyrrolidone) (PVP) on the surface of silver nanocubes by the peptides was investigated. The primary sequences of the peptides were designed such that they enable the covalent attachment to silver via the cysteine thiols, contain amino acids that can interact via hydrophobic interactions, and therefore are likely to form tightly packed films. Finally, the peptides contained UV-vis and SERS markers, allowing the dynamics of the biomolecule attachment to the nanoparticles to be monitored spectroscopically. The ligand exchange was observed for nanocubes suspended in solution and supported on a dielectric substrate. Formation of the peptide film around the nanocubes was confirmed by electron microscopy and SERS measurements. The film thickness was found to be 4-6 nm and independent of peptide solution concentration, suggesting multilayer formation. The surface density of these cysteine-containing peptides was found to be between 0.59 and 4.92 molecules per nm.