CLOSE-PACKED ADSORPTION OF F(AB')(2) FRAGMENT OF IMMUNOGLOBULIN-G ON PLASMA-POLYMERIZED ALLYLAMINE FILM

Plasma-polymerized films were formed on flat glass plates using allyla mine, acrylic acid, acrolein, and allylcyanide as monomers. Adsorption of immunoglobulin G (IgG), F(ab')(2)-IgG, Fc-IgG and human serum albu min (HSA) on these plasma-polymerized films and on commercially availa ble polymer plates usually used as substrata for immunoassay was measu red. Here, F(ab')(2)-IgG and Fc-IgG are fragments of IgG. The adsorpti on isotherm followed the Langmuir equation, from which the binding con stant 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)-I gG. From saturation binding data, diameters of area occupied by adsorb ed proteins were calculated assuming that the adsorbed protein formed a monolayer on the film. Comparing these values with molecular size, w e inferred that F(ab')(2)-IgG took a close-packed ''end-on'' orientati on on plasma-polymerized allylamine while it took a ''side-on'' orient ation on plasma-polymerized acrylic acid.