The Orientation of BN-Related Peptides Adsorbed on SERS-Active Silver Nanoparticles: Comparison with a Silver Electrode Surface

We used surface-enhanced Raman scattering (SERS) to characterize the adsorption behavior of bombesin (BN) and five BN-related peptides, including phyllolitorin, [Leu(8)]phyllolitorin, neuromedin C (NMC), neuromedin B (NMB), and PG-L (Pseudophryne guntheri), in a silver colloidal solution. Our experiments show that the pyrrole coring of the Trp and aromatic ring of Phe of these peptides are preferentially adsorbed on silver nanoparticles. However, the geometry of the rings and the strength of the interactions with this surface vary among peptides. Additionally, these peptides are weakly coordinated to the colloidal silver surface through the C=O fragment of a peptide bond, between Gin/Leu/His and Trp residues, and C-N-C and S-C fragments. Also, using the recently reported SERS spectra of these peptides immobilized onto an electrochemically roughened silver electrode surface, we demonstrate substrate-induced changes in the adsorption behavior of these peptides. Comparative analysis indicates that the interactions between peptides and the enhancing surfaces depend strongly on the geometry of the Trp, -CONH-, and S-C fragments of these biomolecules etched on the surfaces.