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

immunodiagnostic tests. The recent advances in polymer In this work the interaction of an a-CRP IgG protein with science have made it possible to produce uniform latexes functionalized latexes that have acetal groups on their surfaces with desired size and surface characteristics. Thus, it is possihas been studied. Two acetal latexes with similar amounts of ble to obtain latex particles with specific functional groups surface acetal groups but different surface charge densities were which can covalently bind antibody molecules via amine used. Some experiments on the physical and chemical adsorption groups. From the point of view of its immunological applicaof the IgG onto these polystyrene beads have been performed, tion, the covalent bond of proteins to the particle surface and several latex–protein complexes with the IgG physically or prevents the physical desorption of the proteins and retains chemically bound to the surface were obtained by modifying the the native conformation of these biomolecules. Most of the incubation conditions. In the covalent coupling experiments of the IgG, the physically adsorbed protein was removed by redisperstudies of covalent coupling of proteins were developed with sion of the complexes in the presence of a nonionic surfactant carboxylated latexes and require some chemical reaction (1– (Tween 20). After this treatment the final amount of protein on 3). Recently, several authors (4–7) indicated that the use of the latex surface was around 80% of the total protein initially aldehyde groups on the surface could simplify the covalent adsorbed. The latex–protein complexes that formed were characbinding of the protein due to the direct reaction between the terized from the electrokinetic point of view by measuring their aldehyde groups of the surface and the amine groups of the electrophoretic mobilities versus the pH, in order to detect any protein molecules. However, due to the chemical unstability difference between the particles when the protein is physically or of the aldehyde groups, they tend to decompose with time, chemically coupled. The isoelectric point ( iep) of the complexes losing their capacity to link the proteins. As suggested by was around pH 4, where they will be unstable because the electroKapmeyer et al. (8, 9) , another possibility is to produce latex static repulsion cannot stabilize the particles. At neutral and basic particles with acetal groups on the surface. These groups can pH, the electrophoretic mobility values of the latex–protein particles seem to predict a good colloidal stability which is a very be transformed to aldehyde groups to produce the covalent important aspect when looking for its application in the field of coupling of the proteins, by moving the medium to acid pH. the clinical diagnostic. The redispersion of the complexes in the In the present work, we have focused our attention on the presence of Tween 20 modified the electrokinetic behavior of the interaction of an a-CRP (C-reactive protein) IgG protein particles, especially at pH 4 and 5, which seems to indicate an with functionalized latexes that have acetal groups on their interaction between the surfactant and the protein molecules surface. We used two acetal latexes with a similar amounts which could reduce the immunoreactivity of the latex–protein of surface acetal groups but with different surface charge complexes. q 1998 Academic Press densities of carboxyl groups (10). As a first step, the physi