Immunoreactivity of adsorbed anti human chorionic gonadotropin studied with an optical waveguide interferometric sensor.

A study on the immunoreactivity of adsorbed alpha hCG molecules as a function of substrate hydrophobicity and protein coverage is presented. The experiments were performed with a planar waveguide interferometrical immunosensor. The substrate hydrophobicity and the antibody density were found to be of major importance for the immunoreactivity of the adsorbed antibodies. A combination of a hydrophobic (contact angle > or = 80 degrees) substrate and only a fraction (approximately 0.3) of a monolayer of antibodies gives the highest immunoreactivity. However, the immunoreaction affinity constant of the active antibodies is found to be essentially independent of the substrate hydrophobicity. The experimental results indicate that the orientation and not the conformation of the active antibodies on the substrate is dependent on the substrate hydrophobicity.