COVALENT BINDING OF PROTEINS TO ACETAL-FUNCTIONALIZED LATEXES - I - PHYSICS AND CHEMICAL ADSORPTION AND ELECTROKINETIC CHARACTERIZATION

In this work the interaction of an a-CRP IgG protein with functionaliz ed 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 bea ds have been performed, and several latex-protein complexes with the I gG physically or chemically bound to the surface were obtained by modi fying the incubation conditions. In the covalent coupling experiments of the IgG, the physically adsorbed protein was removed by redispersio n of the complexes in the presence of a nonionic surfactant (Tween 20) , After this treatment the final amount of protein on the latex surfac e was around 80% of the total protein initially adsorbed, The latex-pr otein complexes that formed were characterized from the electrokinetic point of view by measuring their electrophoretic mobilities versus th e pH, in order to detect any difference between the particles when the protein is physically or chemically coupled. The isoelectric point (i ep) of the complexes was around pH 4, where they will be unstable beca use the electrostatic repulsion cannot stabilize the particles. At neu tral and basic pH, the electrophoretic mobility values of the latex-pr otein 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 pre sence of Tween 20 modified the electrokinetic behavior of the particle s, especially at pH 4 and 5, which seems to indicate an interaction be tween the surfactant and the protein molecules which could reduce the immunoreactivity of the latex-protein complexes. (C) 1998 Academic Pre ss.