Vibrational Sum-Frequency Scattering as a Sensitive Approach to Detect Structural Changes in Collagen Fibers Treated with Surfactants.

Optimizing protocols so that the structure of the collagen fibers in the extracellular matrix remains intact during the decellularization process requires techniques with high structural sensitivity, especially for the surface region of the collagen fibers. Here, we demonstrate that vibrational sum-frequency scattering (SFS) spectroscopy in the protein-specific amide I region provides vibrational spectra and scattering patterns characteristic of protein fiber networks self-assembled in vitro from collagen type I, which are kept in aqueous environments during the analysis. At scattering angles away from the phase-matched direction, the relative strengths of various polarization combinations are highly reproducible, and changes in their ratios can be followed in real time during exposure to sodium dodecyl sulfate surfactant solutions. For the fibers in this work, a scattering angle of about 22° provided specificity for the surface region of the fibers, as it allowed monitoring of immediate structural changes during the surfactant exposure. With further development, we hypothesize that the information from the SFS characterization of collagen fibers may complement information from other techniques with sensitivity to the overall structure, such as second-harmonic generation imaging and infrared spectroscopy, and provide a more complete understanding of fiber molecular structures and interactions during exposure to various environments and conditions.