Immobilization of glucose oxidase using CoFe2O4/SiO2 nanoparticles as carrier

► The immobilized GOD enhances the thermal stability and exhibits a strong endurance to the variation of solution pH, high temperature, and long-term storage. ► A facile chemical method was developed to prepare monodisperse CoFe2O4/SiO2 NPs with desired size and narrow size distributions. ► As-prepared CoFe2O4/SiO2 NPs have superparamagnetism, indicating that the CoFe2O4/SiO2 NPs can be used as an effective carrier for the GOD immobilization. Aminated-CoFe2O4/SiO2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber 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 3h, solution pH of 7.0 and 0.4mg GOD (in 3.0mg carrier). The immobilized GOD showed maximal catalytic activity at pH 6.5 and 40°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°C for 25min, whereas free enzyme had only 20% of initial activity after the same incubation. After kept at 4°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 KM (Michaelis–Menten constant) values for immobilized GOD and free GOD were 14.6mM and 27.1mM, respectively.