Immobilization of protein on monodispersed colloidal silica with poly(ethylene glycol) spacer and application of the composites to immunological agglutination tests

Surface modifications of monodispersed colloidal silica with poly(ethylene glycol) (PEG-COOH) silane coupling agents having a carboxyl end group, the successive immobilization of bovine serum albumin (BSA) and the application of the protein composites as an immunolatex were investigated. The reaction of the colloidal silica suspended in ethanol with the PEG-COOH coupling agents in the presence of small amounts of aqueous ammonia successfully gave PEG-COOH/SiO2 composites, retaining the particle size. Covalent binding of BSA to PEG/SiO2 composites was achieved by an activated ester method in the presence of an excess of the protein in pH 7.0 buffer. The agglutination tests using the BSA-PEG/SiO2 particles with anti-BSA antibody and gamma-globulin derived from rabbits suggested applicability of the protein-PEG/SiO2 composites as immunoassay latexes.