Scanning angle reflectometry study of the structure of antigen-antibody layers adsorbed on silica surfaces

A layer of Immunoglobulin G (IgG) adsorbed on silica is brought into contact with a solution of IgG antibodies that specifically bind to the first protein. Both the thickness and the density of the resulting layer are studied using scanning angle reflectometry. Initially, the incoming antibodies appear to embed themselves in the preadsorbed protein layer. The structure of the layer relaxes with time, becoming both thicker and less dense. This evolution in structure continues long after the total surface concentration stops evolving. The final protein layer is surprisingly thick: as much as three times the length of a single protein molecule. We hypothesize the formation on the surface of an antigen/antibody complex that subsequently turns there, as previously postulated for the exchange process. This would expose the antigen to further interactions with antibodies in solution, allowing the formation of a triple layer.