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Luminescent core-shell polymer particles carrying amino groups for covalent immobilization of enzymes were synthesized for practical applications in immunoassays. The polystyrene core particles were synthesized by miniemulsion polymerization of oil-in-water emulsion styrene droplets dissolving 2-(2-chloropropionyl)ethyl methacrylate and the europium complex emulsified with 2-methacryloyloxyethyl-N,N-dimethyl-N-n-dodecylammonium bromide. The red luminescence attributed to europium complexes embedded in the core particles was observed upon UV irradiation. The PSt-g-POEGMAx-NH 2 aminated core-shell particles were prepared by surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMAx), followed by Gabriel synthesis. The densities of grafted chains were determined by the composition, the hydrodynamic diameters, and the fluorescence labeling method. POEGMAx-grafted chains were found to affect the dispersion stability of the particles. The nonspecific adsorption of bovine serum albumin was suppressed by the POEGMAx-grafted chains. The enzymatic activity of horseradish peroxidase covalently bound to the terminal amino groups of POEGMAx-grafted chains was evaluated by colorimetric immunosorbent assay. KeywordsMiniemulsion polymerization • Surface-initiated atom transfer radical polymerization (SI-ATRP) • Oligo(ethylene glycol) methyl ether methacrylate (OEGMAx) • Core-shell polymer particles • Europium complexes • Activated-horseradish peroxidase (activated-HRP) * Tatsuo Taniguchi