Forces acting on particle-enhanced immunoassays

The aim of the present work is to study the role of the different forces in volved in the agglutination of immune gamma-globulin (IgG) covered latex pa rticles due to antigen-antibody reaction. An experimental investigation on the adsorption of IgG molecules on three latexes with different surface cha rge densities is described. Photon correlation spectroscopy was used to det ermine the hydrodynamic layer thickness of the IgG molecules adsorbed on th e latexes. In order to get an insight into the forces acting between two antibody-cove red particles approaching each other, the colloidal stability and immunorea ctivity of these biocomplexes were studied. They can be stabilized by elect rostatic or hydration forces. The immunological agglutination of IgG-immobi lized latex particles due to the addition of the antigen was quantified thr ough scattered light intensity measurements. The immunoresponse increases w ith ionic strength of the medium until a maximum value is achieved. Above t his maximum, the immunoreactivity decreases.