On the structure of electrical double layer of IgG immobilized on polystyrene microspheres

Latex particles used in the development of immunoassays usually present stability problems when the antibody is attached to the surface. This work is an attempt to know the potential distribution parameters around these complexes by electrokinetic measurements. The conversion of mobility data into zeta-potential was carried out by different theoretical approaches developed by Smoluchowski (classical equation), O'Brien and White, and Dukhin and Semenikhin. The zeta-potential calculated with allowance for electrical double layer (e.d.l.) polarization was substantially greater than zeta calculated according to the classical electrokinetic theory. The greater values of zeta D-S in comparison with zeta O-W were readily explained on the basis that in the first theory, the contribution to polarization from all ions of the diffuse layer was taken into account, whereas O'Brien and White accounted for only the ions of the hydrodynamically mobile part of the e.d.l. This is an indication that the anomalous surface conductance of latex particles coated by IgG molecules is much higher than that of bare latex particles.