Investigation of functionalized biomembranes by ATR - SEIRA spectroscopy with polarized light

Surface enhanced FTIR spectroscopy (SEIRA) with polarized light can be used to investigate the structure of functionalized membranes. We have used this method to characterize lipid membranes containing integral membrane proteins. The Ge ATR crystal was coated by a 9 nm layer of Ag clusters before adsorbing the membrane. The dipoles of the clusters get excited by the evanescent field. The observed spectra show an enhanced absorption of different functional groups. The enhancement factor depends upon the polarization of the incident light and depends upon the orientation of this groups towards the cluster surface. This allows the detection of the structure and orientation of the membrane fragments at the interface of the clusters.