Co-B/SiO2/NH2 magnetic nanoparticles (NPs) were prepared from a silica shell-coated Co-B core using the Stober method and amine-modification on the surface. Glucose oxidase (GOD) was covalently immobilized on the surface of Co-B/SiO2/NH2 NPs using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) as an activating agent. The magnetic NPs characteristics, such as the synthesis of Co-B/SiO2/NH2 NPs, effect of pH, temperature, and concentration of buffer for enzyme immobilization, were investigated. The optimal reaction conditions for immobilization were determined to be 0.1 M of phosphate buffer solution, pH 7.0, and 5 degrees C. In the case of immobilized GOD without D-glucose and with 0.1 M of D-glucose for blocking, 22.98 U/g and 24.83 U/g of their original activity were retained after 7 reuses, respectively. (C) 2012 Elsevier Ltd. All rights reserved.