Effects of the Ionic Environment, Charge, and Particle Surface Chemistry for Enhancing a Latex Homogeneous Immunoassay of C-Reactive Protein

Abstract

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

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“…However, this hypothetical mechanism is not very plausible. Pérez-Amodio et al [47] measured the immunoreactivity of IgG-latex particles in solutions containing, independently, 100 mM NaCl, NaNO 3 , and NaSCN. If conformational changes occurred in the antibody molecules, a loss in immunoreactivity should be observed.…”

A Piezoelectric Immunosensor Based on Agglutination Reaction with Amplification of Silica Nanoparticles

“…25,26 Since the dimensional configurations and electrostatic states of proteins are commonly pH-dependent, it is expected that the pH value would play a vital role in the immunoagglutination performances. The effects of pH values on the frequency responses are shown in Figure 2.…”

“…The salt in the assay buffer solution might promote both immunorecognition/agglutination and colloidal instability. 25 In addition, an appropriate ionic strength in the buffer solution is important in suppressing non-specific precipitation of labile substances in the samples. 13 Other experimental conditions were the same as above.…”