Electrokinetic characterization and colloidal stability of polystyrene latex particles partially covered by IgG/a-CRP and m-BSA proteins

Abstract

In this work the competitive coadsorption of immunoglobulin IgG and bovine serum albumin (BSA) proteins on a sulfate polystyrene latex has been studied. The competitive coadsorption experiments were carried out by changing the initial concentration of both proteins ([m-BSA] or [IgG/a-CRP]) in order to cover different possibilities of competition. By changing the pH and the ionic strength during the incubation, it was possible to obtain latex—protein complexes with different degrees of coverage by each protein. These complexes were characterized electrokinetically under several different redispersion conditions and their colloidal stability was also determined. By combining both results it is possible to establish that, at neutral pH, electrostatic repulsion is the main factor governing the colloidal stability. This stability appeared when negatively charged BSA molecules constituted the majority protein on the particle surface. However, the immunoreactivity of the sensitized latexes was sufficient with a partial coverage by IgG molecules. Therefore the properties of the latex—protein complex depended on the percentage of BSA or IgG adsorbed and on the charge state of the proteins at the redispersion pH. By using specific incubation conditions, latexes covered by different percentages of IgG/BSA were obtained, which showed high colloidal stability and good immunoreactivity.