Construction of a novel multilayer system and its use for oriented immobilization of immunoglobulin G

In this contribution, we have developed a novel multilayer system composed of 3-aminopropyltrimethoxysilane (APTS), biotin, streptavidin and biotinylated protein A on the Si(1 0 0) surface to immobilize of immunoglobulin G (IgG) molecule. Existence of the first APTS layer covalently attached on the silicon surface was revealed by X-ray photoelectron spectroscopy (XPS). Average thickness of the APTS overlayer was estimated by spectroscopic ellipsometry analysis as 6.3 nm. The surface topography of the APTS overlayer observed by atomic force microscopy is found to be considerably different from the hydroxylated silicon surface and many additional islands of various heights are observed over the substrate. The water contact angle of the APTS overlayer was determined as 38°, whereas that of the hydroxylated silicon was obtained as 6°, indicating the difference in their surface hydrophobicility. Furthermore, multilayer studies on the APTS overlayer were carried out by using biotin, streptavidin and fluorescein-labeled biotinylated protein-A molecules. The fluorescence images obtained by fluorescence microscopy showed the formation of the multilayer on the Si(1 0 0) surface. The results indicated that the protein A-terminated surfaces can be used to immobilize IgG molecules in a highly oriented manner and maintain IgG molecular functional configuration on the multilayer system.