The molecule design of polymer additive with smart bioactive covalently attached to Si(100) disc surface

In this study, a novel multilayer system consisting of 12- hydroxydodecanoic acid (HDA), poly(dimethylsiloxane), bis(3- aminopropyl) terminated [NH2-(PDMS)n=2500-NH2], biotin, streptavidin, and biotinated Protein A covalently attached on Si(100) surface was formed and used for the oriented immobilization of immunoglobulin G (IgG). These molecules were chosen for the following reasons. 1) The HDA molecule has both good mechanical properties and two different functional groups such as hydroxyl and carboxylic acid. Therefore, it is one of the most useful molecule for the preparation of self-assembled monolayer (SAM). 2) NH2-(PDMS)n=2500-NH2 was selected as a flexible molecule with terminal amino groups and it has more freedom to tilt or bend for attachment of biotin to all of the available amino groups. 3) Biotin (vitamin H) has an extremely high binding constant (Kd=10-15 M) tetravalent streptavidin. 4) When streptavidin is bound to the overlayer, a biotinated Protein A is readily immobilized. 5) Biotinated Protein A is specific biomolecule for IgG immobilization. The thicknesses of the prepared multilayer systems were measured by spectroscopic ellipsometry (SE). The surface characteristics were analyzed by attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), fluorescance microscopy and water contact angle measurements. As a result, the combination of ellipsometry and Protein A terminated surface will be possessored the potential to be further developed into an efficient immunosensor protein chip.Key Words: Nanotechnology, self-assembled monolayers, protein chip, immunosensor