The binding of antigen by immobilized antibody: Influence of a variable adsorption rate coefficient on external diffusion limited kinetics

Abstract

The influence of reaction-order and external mass-transfer limitations on the binding kinetics of antigen in solution to antibody covalently attached to a cylindrical fiber-optic biosensor is presented. Both single-step and dual-step binding of antigen to antibody are considered. Nonspecific binding and heterogeneity in binding are also mentioned. An increase in the Damkohler number decreases 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 reactions of orders one, one and one-half, and two. As 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. Nondimensional plots presented in the analysis help extend the analysis to different antigen-antibody systems. A decrease in the external diffusional limitations decreases 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. A variable rate coefficient for adsorption provides a more realistic picture of the events occurring on the fiber-optic surface. A decreasing variable rate coefficient for adsorption has the same effect as that of a decreasing Damkohler number, and also introduces nonlinearity in the attachment of the antigen to the antibody immobilized on the surface.