Efficient immobilization of glucose oxidase on mesoporous MIL-125 and their catalytic activities

Abstract

Glucose oxidase (GOD), a popular enzyme used in pharmaceutical, food, bio-sensor and other fields, can well catalyze the oxidation of glucose to produce gluconic acid and hydrogen peroxide. The main limitation for the applications of free enzyme is its less preferable owing to its weaker activity against to changeable conditions such as pH, temperature, and organic solvent. The immobilization is thought to be an effective way to improve the stability of GOD under harsh conditions. In this study, MIL-125 was applied as a fixing carrier to anchor GOD for the first time. The synthesized MIL-125 was characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption-desorption and DFT pore size distribution. The FT-IR spectra were employed to study the structural stability and interface interaction of MIL-125 with GOD. Compared to the previously reported GOD-related adsorption results, the higher adsorption capacity of GOD was obtained on MIL-125. The adsorption kinetics and isotherm analyses indicated that the adsorption process of GOD on MIL-125 was a spontaneous endothermic process, which was more in line with the pseudo-second-order kinetic model. The enzyme activity assay showed that the values of Km and Vmax for immobilized GOD on MIL-125 were 14.482 mmol L−1 and 0.356 mmol⋅L−1⋅min−1, respectively, which were lower than those of free GOD. But, compared to free GOD, the immobilized GOD showed less sensitivity to the changes in temperature, pH values and organic solvent. After six cyclic catalytic reactions, the immobilized GOD remained over 43.79% of its initial activity. The endurability tests showed that the immobilized GOD showed 43.41% of its initial activity after storage for 21 days at room temperature; meanwhile, the free GOD almost lost its initial activity at the end of 3 days under the same condition. The results demonstrated that the MOF-immobilized enzymes were more stable and had a broader potential application in the enzyme immobilization engineering.