On Some Aspects of the Adsorption of Immunoglobulin-G Molecules on Polystyrene Microspheres

An experimental investigation on the adsorption of immuno-globulin-G on polystyrene microspheres is described. Two negatively charged polystyrene latexes of different surface charge density (σ0) were prepared by an emulsifier-free method. Rabbit IgG molecules were adsorbed on both latex samples. Adsorption isotherms at different ionic strengths and pH were performed. In all cases the adsorption isotherms showed well-defined plateau. The more negatively charged polystyrene latex showed a higher adsorption of IgG molecules at pH values lower than 8. Both samples of latex reached a maximum adsorption at pH = 6.0. The isoelectric point of the IgG-latex complex was around 5.5, it was lower than the isoelectric point range of the IgG molecules, which was from 6.1 to 8.7. This difference indicates that the negative charge of the latex surface at least partially compensates the positive charged groups of the protein The differences in the colloidal stability of the sensitized particles is not explained by the electrophoretic mobility values. The colloidal stability of the IgG-latex complex is not only determined by the electrical charge of that complex but also by certain properties of the protein, such as interactions between hydrophobic domains of the adsorbed IgG molecules.