Binding kinetics of antigen by immobilized antibody: influence of reaction order and external diffusional limitations.
The influence of reaction order and external mass transfer limitations on the binding kinetics of antigen in solution to antibody covalently or non-covalently attached to a cylindrical fiber-optic biosensor is presented. Both single-step and dual-step binding of antigen to antibody is considered. The rate of attachment of antigen to antibody is linear for all reaction orders in the time frame (100 min) considered. The rate of attainment of saturation levels of antigen in solution close to the surface is very rapid (within 20 min). An increase in the presence of mass transfer (denoted by a Damkohler number increase) decreases the saturation level of the antigen close to the surface, and the rate of antigen attachment to the antibody covalently or non-covalently bound on the surface for one-half, one, one and a half, and second-order reaction. As intuitively expected, an increase in the initial antigen concentration in solution increases the saturation level of the antigen close to the surface, and the rate of antigen attachment to the antibody covalently bound on the surface for all the reaction orders considered. Non-dimensional plots presented in the analysis help extend the analysis to different antigen-antibody systems. A decrease in the external diffusional limitations has an effect of decreasing the effect of reaction order on the saturation levels of antigen close to the surface and the rate of attachment of the antigen in solution to the antibody on the surface.