Controlling immunoglobulin G orientation on a protein-A terminated bilayer system

In this study, a bilayer system composed of N-[3-trimethoxysilyl propyl]-ethylene diamine (TEDA) and protein-A on silicon wafer was prepared by a simple two-step procedure. Self-assembly deposition of TEDA at optimal conditions resulted in the formation of homogeneous self-assembled monolayers (SAMs) ~ 2.3 nm thick with the surface roughness ~ 0.38 nm. The height value of protein-A overlayer was found to be ~ 3.5 nm, which is within experimental error of the diameter of a single protein-A (3 nm). Immunoglobulin G (IgG) molecules were then immobilized on the bilayer system by protein-A - IgG specific interactions. Using this very simple approach, the IgG layer was formed almost of a monomolecular layer for longer adsorption time (~ 100 min), and it was packed densely for adsorption time longer than 100 min, which resulted in the increase of the amount of IgG immobilized. The use of a bilayer system composed of TEDA and protein A on silicon wafer opens the door for a fundamental understanding of how protein A affects IgG orientation on the surface and also indicates a useful guide to designing surfaces for applications such as immunosensors and biochips.