Immobilization of glucose oxidase on chitosan–SiO2 gel

Novel porous gels of chitosan–SiO2 were prepared by coupling chitosan with tetramethoxy silicane through the sol–gel approach at ambient conditions. The characteristics of the gel were evaluated using Fourier Transform IR spectrophotometer and scanning electron microscopy. The optimal ratio (w/w) of tetramethoxy-silicane/chitosan was ascertained to be 3.5 or 4. The swelling ratio of the produced gel was about 45% in distilled water. Glucose oxidase (GOD) was selected as a model enzyme to assess its potential applicability for the enzyme immobilization purpose. Under an optimized condition (formaldehyde 20 mg/ml, GOD 2 mg/ml and pH 6.5), the enzyme immobilization yield (IY%) was 97% with the immobilized GOD activity of 1585 U/g. The Michaelis constant (Km) for immobilized GOD was disclosed to be 36.5 mmol/l by Lineweaver–Burk plot at 25 °C, and the highest enzyme activity was allowed at pH 5.6, identical to that of the free enzyme. The immobilization procedure stabilized the enzyme substantially as 86 and 56% of the immobilized GOD activity could still be discerned after being kept at 30 °C for 10 and 15 days, respectively, whereas most of the free enzyme turned inactive after a five-day standing in the same manner.