Protein co-adsorption on different polystyrene latexes: Electrokinetic characterization and colloidal stability

The latex agglutination immunoassay technique uses polymer colloids as a carrier for the adsorbed proteins to enhance the antigen-antibody reaction. Competitive coadsorption of IgGaCRP and m-BSA proteins on polystyrene latexes with different functionality (sulfate and sulfonate groups) was carried out looking for the increase in the immunoreactivity and colloid stability of latex-protein complexes. The preferential adsorption of a protein is also studied, comparing both surface types. Regarding the application in the development of a diagnostic test system, it is necessary to study the latex-protein complexes from an electrokinetic and colloid stability point of view. The presence of protein on the surface latex shifts the iso-electric point (i.e.p.) of the latex-protein complexes to pH values near the i.e.p. of the protein which is the majority. Thus by the adsorption of m-BSA we can obtain complexes with the i.e.p. near pH 5 and, therefore, with a significant electrostatic repulsion at neutral pH. Due to the higher surface charge density of the sulfonate latexes there is a higher adsorption of both proteins, which can provide a better colloidal stability (by the adsorption of m-BSA) and a better immunoreactivity (by the adsorption of IgG).