UBC Theses and Dissertations
A surface and colloid chemical study of the interaction of proteins with polystyrene latex (PSL) Olal, Andrew Dandy
In this thesis various physicochemical factors which determine the characteristics of latex agglutination immunoassays are examined. A model of antibodies reacting with antigen (bovine serum albumin; BSA) adsorbed to the surface of polystyrene latex (PSL) beads was examined. The adsorption studies of BSA to PSL showed that the mass of BSA adsorbed at saturation depends on the type of polystyrene latex. Latexes with highly hydrophobic surfaces adsorbed more BSA molecules than those with lower hydrphobicity. Desorption studies showed that latexes that maximize adsorption lost the lowest fraction of their bound BSA molecules following extensive buffer wash. Partial desorption of BSA from PSL was achieved by the addition of detergent, whereas the addition of more BSA molecules or other macromolecules such as PEG or IgG did not displace the adsorbed BSA molecules. Examination of the material removed from the surface of the latexes by SDS-PAGE analysis showed that the composition of the adsorbed layer was enriched in the higher molecular weight oligomers of BSA, relative to their concentrations in the stock solution. A model in which adsorbed protein is assumed to undergo a polymerization reaction provides a general explanation of the observed results. Studies of polyclonal antibody (anti-BSA IgG) binding to antigen-coated PSL showed that the surface concentration of bound antibody depends on the surface concentration of antigen on the latex particles and on the availability of PSL surface area not occupied by antigen. Analysis of shear induced aggregation results show that for low surface coverage of latex particles by protein antigen in stable suspension, relatively low concentrations of specific antibodies are required to cause agglutination. Increasing surface density of antigen requires significantly higher concentrations of specific antibodies to produce agglutination. For a given surface coverage of antigen, results show that increasing the shear rate decreases the antibody concentration necessary to produce a given degree of agglutination. A remarkable structure formation and long range ordering exhibited by floes of latex coagulating in salt under intermediate shear rates was observed. This structure formation was not observed during antibody-induced agglutination under shear.
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