Close-Packed Adsorption of F(ab′)2 Fragment of Immunoglobulin G on Plasma-Polymerized Allylamine Film

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Abstract
Plasma-polymerized films were formed on flat glass plates using allylamine, acrylic acid, acrolein, and allylcyanide as monomers. Adsorption of immunoglobulin G (IgG), F(ab′)2-IgG, Fc-IgG and human serum albumin (HSA) on these plasma-polymerized films and on commercially available polymer plates usually used as substrata for immunoassay was measured. Here, F(ab′)2-IgG and Fc-IgG are fragments of IgG. The adsorption isotherm followed the Langmuir equation, from which the binding constant and saturation binding were estimated. We found that in general, a cationic surface has higher affinity for protein adsorption than an anionic surface. Among the surfaces examined, the plasma-polymerized allylamine surface showed the highest binding capacity for F(ab′)2-IgG. From saturation binding data, diameters of area occupied by adsorbed proteins were calculated assuming that the adsorbed protein formed a monolayer on the film. Comparing these values with molecular size, we inferred that F(ab′)2-IgG took a close-packed “end-on” orientation on plasma-polymerized allylamine while it took a “side-on” orientation on plasma-polymerized acrylic acid.