Preparation of polymeric monolayers covalently attached to Si(100) surface by surface-initiated atom transfer radical polymerization and their use for the oriented immobilization of immunoglobulin G

In this study, surface-initiated atom transfer radical polymerization (SI-ATRP) of N-isopropylacrylamide (NIPAM) on Si(100) surface conducted in attempt to create controllable Poly(N-isopropylacrylamide) (PNIPAM) and functional-terminated PNIPAM brushes. Chain transfer agents were added into polymerization medium to obtain functional-terminated polymer brushes. For synthesis of amino or hydroxyl-terminated PNIPAM brushes, cysteamine or 2-mercaptoethanol were used, respectively. The polymerization was controlled by adding two different chain transfer agents that were in five different concentrations in polymerization solution, in this way polymer brushes having different film thicknesses were synthesized onto silicon wafer surfaces. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FT-IR) were used for structural characterization of polymer brushes. The hydrophilic/hydrophobic behaviours of PNIPAM and amino or hydroxyl-terminated PNIPAM brushes were determined by water contact angle measurements. PNIPAM brushes and functional-terminated PNIPAM brushes showed hydrophilic character and increasing of concentration of chain transfer agent, increasing of hydrophilic character of polymer brushes were observed. The thermal phase transitions of PNIPAM brushes were also investigated by contact angle measurements over a range of temperature. These measurements showed that PNIPAM brushes had two different thermal phase transition temperatures at 27 and 38 oC between 25-45 oC. Atomic force microscopy (AFM) images also showed that the SI-ATRP method suggest to obtain homogeneous polymer brushes. While polymer brushes covalently attached to silicon surfaces were growing via atom transfer radical polymerization, at the same time free polymer chains were also formed in the polymerization solution. As a consequence of increasing of concentration of chain transfer agent, decreasing of polymer film thicknesses of polymer brushes were determined by ellipsometry and decreasing of number average of molecular weights of free polymers in solution were determined by size exclusion chromatography (SEC). The fluorescence images were obtained by fluorescence microscopy in order to determine surface patterns of polymer brushes. Many fluorescence signals were obtained on fluorescence image of immunoglobulin G (IgG) immobilized amino-ended polymer brushes. Increasing of film thicknesses due to the protein adsorption on the amino terminated surfaces were also determined by ellipsometry. The thickness of the IgG layer found to be 3.89±0.79 nm. Finally, based on the ellipsometric analysis, it was concluded that the IgG is adsorbed on the protein A terminated layer in the manner that its Fc (the fragment crystallizable) domain is bonded to the protein A layer and the Fab (the fragment antigen binding) domains face away from the surface.