Covalent Binding of Proteins to Acetal-Functionalized Latexes. I. Physics and Chemical Adsorption and Electrokinetic Characterization

Abstract

In this work the interaction of an a-CRP IgG protein with functionalized latexes that have acetal groups on their surfaces has been studied. Two acetal latexes with similar amounts of surface acetal groups but different surface charge densities were used. Some experiments on the physical and chemical adsorption of the IgG onto these polystyrene beads have been performed, and several latex–protein complexes with the IgG physically or chemically bound to the surface were obtained by modifying the incubation conditions. In the covalent coupling experiments of the IgG, the physically adsorbed protein was removed by redispersion of the complexes in the presence of a nonionic surfactant (Tween 20). After this treatment the final amount of protein on the latex surface was around 80% of the total protein initially adsorbed. The latex–protein complexes that formed were characterized from the electrokinetic point of view by measuring their electrophoretic mobilities versus the pH, in order to detect any difference between the particles when the protein is physically or chemically coupled. The isoelectric point (iep) of the complexes was around pH 4, where they will be unstable because the electrostatic repulsion cannot stabilize the particles. At neutral and basic pH, the electrophoretic mobility values of the latex–protein particles seem to predict a good colloidal stability which is a very important aspect when looking for its application in the field of the clinical diagnostic. The redispersion of the complexes in the presence of Tween 20 modified the electrokinetic behavior of the particles, especially at pH 4 and 5, which seems to indicate an interaction between the surfactant and the protein molecules which could reduce the immunoreactivity of the latex–protein complexes.