Aminated-CoFe2O4/SiO2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StOber method. Glucose oxidase (GOD) was immobilized on CoFe2O4/SiO2 NPs via cross-linking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, cross-linking time of 3 h, solution pH of 7.0 and 0.4 mg GOD (in 3.0mg carrier). The immobilized GOD showed maximal catalytic activity at pH6.5 and 40 degrees C. After immobilization, the GOD exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 80% of its initial activity after the incubation at 50 degrees C for 25 min, whereas free enzyme had only 20% of initial activity after the same incubation. After kept at 4 degrees C for 28 days, the immobilized and free enzyme retained 87% and 40% of initial activity, respectively. The immobilized GOD maintained approximately 57% of initial activity after reused 7 times. The K-M (Michaelis-Menten constant) values for immobilized GOD and free GOD were 14.6mM and 27.1mM, respectively. (C) 2011 Elsevier B. V. All rights reserved.