Characterization of the Urotensin II Peptide by SERS Using Silver Nanoparticles

ABSTRACT In this work, the vibrational properties of a potent vasoconstrictor—human Urotensin II (U‐II) peptide—were investigated for the first time using Raman and surface‐enhanced Raman scattering (SERS) technique. For this purpose, silver nanoparticles (Ag NPs) with a size of 65 ± 5 nm were synthesized, and a protocol for “gentle” washing of samples from stabilizers, reducing agents, or unstable sample/Ag NPs clusters was developed, which allowed the study of target molecules. It was shown that the interaction of U‐II with the silver surface took place through the functional groups of phenylalanine, tryptophan, and tyrosine amino acids located in the cyclic moiety of peptide, and the S–S bridge between the two cysteines is not broken. It was found that in the adsorbed U‐II peptide –CCSSCC– moiety, the S–S bond is in the gauche conformation, whereas the –CCS– fragment exists in P C –G and P C –T conformations. Additionally, it was shown that U‐II peptide replaced citrate anions on Ag NPs during the process of adsorption. Band assignments for Raman and SERS were proposed.