Reflectometry in kinetic studies of immunological and enzymatic reactions on solid surfaces

An optical method is described, by means of which immunological and enzymatic reactions can be followed at a primary level on a solid surface, without labelling procedures. When plane-polarized light is reflected at a solid surface, there is a minimum in reflectance at a certain angle of incidence, the pseudo-Brewster angle. For example, a layer of protein adsorbed on a silicon surface increases the reflectance with increasing amount of adsorbed material. High sensitivity is obtained because of the large difference in refractive index between silicon and organic material; about 0.1 μg cm^?2 adsorbed protein can be detected. In a model system of human IgG and anti-human IgG, the primary adsorption of IgG on a hydrophobic surface is first measured, and on this IgG-coated surface the binding kinetics of anti-IgG could be measured. The kinetics of proteolytic degradation of IgG-coated surfaces by trypsin was also investigated.