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

Abstract 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/SiO 2 composites, retaining the particle size. Covalent binding of BSA to PEG/SiO 2 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/SiO 2 particles with anti-BSA antibody and γ-globulin derived from rabbits suggested applicability of the protein-PEG/SiO 2 composites as immunoassay latexes.