Synchrotron infrared spectroscopic ellipsometry for characterization of biofunctional surfaces

The structural and thickness homogeneity of different biofunctional surfaces after coating an Au substrate was studied by infrared spectroscopic ellipsometry (IRSE). Monolayer coverage was achieved by washing the samples in aqueous solution. A selected cysteine-modified CHL peptide and an antiglutathione S-transfer (GST) antibody produced a characteristic change in the IR ellipsometric spectra after peptide and antibody adsorption, confirming the biosensing ability of this technique. IR ellipsometric mapping at the synchrotron storage ring BESSY II in Berlin allowed laterally resolved characterization of the protein films. The IR ellipsometric tan Ψ and Δ maps revealed that the protein films are inhomogeneous in structure and thickness after adsorption of the peptide and antibody. The absolute thickness of the protein films varied considerably by up to 3 to 7 nm. We also studied cytosine film; with different thicknesses (d = 58 nm and 125 nm) and a guanine film (d=84nm). For the two cytosine films the synchrotron spectra revealed that the thicker film in particular was rather homogeneous in thickness but inhomogeneous in structure. For the guanine film the shape of vibrational bands in the ellipsometric spectra correlated with anisotropic molecular orientations.