A Raman spectroscopic study of the adsorption of fibronectin and fibrinogen on titanium dioxide nanoparticles

The adsorption of proteins that contain the amino acid sequence Arg-Gly-Asp (RGD) plays a crucial role for the biocompatibility of implant materials. Detailed knowledge of the adsorption process is of great interest because it is a dominant factor that decides on the integration or rejection of an implant by the organism. We have studied the adsorption process on titanium dioxide nanoparticles via two proteins, namely fibrinogen and fibronectin. Bulk protein spectra are compared to spectra of proteins that were adsorbed on TiO2 nanoparticles (as an enlarged model surface for TiO2 implants). In the Raman spectra of the adsorbed proteins a characteristic band occurs that can be assigned to an interaction between TiO2 nanoparticles and the carboxylate groups of the protein. A moderate shift of the amide I band towards higher wavenumbers observed in the adsorbed fibrinogen spectrum in comparison to the bulk protein spectrum is due to conformational changes during the adsorption process. In the spectra of adsorbed fibrinogen the peak area of the multiplet of CH3 and CH2 deformation modes in relation to the amide I Raman peak area is decreased as compared to the spectra of bulk fibrinogen. These spectral features indicate an increasing content of β-sheet and a decrease of α-helical structure content for fibrinogen while for fibronectin an increase of β-sheet structure and a decreasing content of random coil structure was found. The adsorption takes place via the protein side-chains.