Effects of the ionic environment, charge, and particle surface chemistry for enhancing a latex homogeneous immunoassay of C-reactive protein

The role of the solution environment for a light-scattering, latex-particle -enhanced, homogeneous immunoassay of C-reactive protein (CRP) has been inv estigated in order to assess and optimize the immunoagglutination response. Latex particles of 50-170-nm sizes were covalently coupled with an IgG pol yclonal antibody and subjected to an extensive optimization regime. This co nsisted of conditions responsible, in different degrees, for the principal attractive/repulsive forces affecting both colloidal stability and the anti body/antigen interaction: particle size, antibody concentration, ionic stre ngth and species, pH, and amino acid chemistry of the particle surface. Car eful control of these parameters was found to be necessary to achieve the d esired effects of balancing high colloidal stability in the absence of anti gen but promoting a rapid, sensitive, and dose-dependent agglutination with pathological serum samples, In addition, the estimation of fundamental pro perties governing intermolecular interaction (i.e. the "Hamaker" constant a nd critical coagulation concentration) was attempted to order to investigat e a simple, practical means of defining a colloidal/immunoassay system unde r "real conditions" as well as "real time". It is concluded that because ea ch antibody system is unique, a similar optimization should be performed in diagnostic immunoassays of this type to maximize their clinical utility.