Covalent Binding of Proteins to Acetal-Functionalized Latexes. II. Colloidal Stability and Immunoreactivity

Abstract

The present work deals with the study of the colloidal stability and immunoreactivity of acetal-functionalized latex particles covered by different amount of IgG a-CRP protein. This protein has been previously coupled onto the acetal particle surface by covalent binding, and it was possible to obtain latex–protein particles with different degrees of coverage by this protein. The sensitized latex particles were resuspended under several conditions (different pH and ionic strength values), and their colloidal stability was studied by particle size measurements. The latex–protein complexes obtained by covalent binding of the protein show a good colloidal stability at neutral pH and high ionic strength (200 mM), which is a first condition for their application in the immunodiagnostic field. As a final part of this work, the immunoreactivity of several complexes was studied following the changes in the turbidity after the addition of CRP antigen. The immunoreactivity of these complexes depends on their colloidal stability, and treatment with a nonionic surfactant is also important. The surface structure of the latexes has a significant role in the immunological behavior of the complexes because a very high surface charge density can prevent the aggregation of the sensitized particles in the presence of the antigen molecules. The latex–protein complexes obtained by covalent binding show a good immunological response which is not disturbed by the presence of a nonionic surfactant in the reaction medium and is stable with time.