Surface enhanced Raman spectroscopy of collagen I fibrils

Abstract

Collagen fibrils are the main constituent of the extracellular matrix surrounding eukaryotic cells. Even though the assembly and structure of collagen fibrils is well characterized, very little is known about the physico-chemical properties of their surface which is one of the key determinants of their biological functions. One way to obtain surface sensitive structural and chemical data is to take advantage of the near field nature of surface and tip-enhanced Raman spectroscopy. Using Ag and Au nanoparticles bound to collagen type I fibrils, as well as tips coated with a Ag nanoparticles and a thin layer of Ag, we obtained Raman spectra characteristic of the first layer of collagen molecules at the surface of the fibrils. The most frequent Raman peaks were attributed to aromatic residues such as phenylalanine and tyrosine. We also observed in several instances Amide I bands with a full width at half maximum of 10-30 cm-1. The assignment of these Amide I bands positions suggests the presence of collagen-helices as well as alpha-helices and beta-sheets at the fibril’s surface. As a step towards in vivo characterization of collagen fibrils, fascicles removed from tendons were also examined with surface-enhanced Raman spectroscopy.