Improvement on Reusability, Storage Stability and Thermal Stability of Magnetic Graphene Oxide-Immobilized Cholesterol Oxidase

Biosensor using the enzyme cholesterol oxidase (ChOx) was one of the cholesterol detection methods commonly developed because of its good specificity. Immobilization would increase the stability of the enzyme, hence magnetic graphene oxide was chosen as support material because of its high surface area, good thermal conductivity, high number of functional groups, and paramagnetic properties. This work aimed to study the effects of using magnetic graphene oxide as support for the immobilization of cholesterol oxidase. Magnetic graphene oxide was synthesized, and cholesterol oxidase was crosslinked to the material. The immobilized enzyme was confirmed by the appearance of the P-O-C group at a wavenumber of 920 cm^-1 and a C=O group at a wavenumber of 1724 cm^-1, accompanied by the surface structure of the material becoming much rougher. The result revealed that after ten cycles, immobilized ChOx maintained 7.10% of its initial activity. The activity retained after being kept at 4^oC for 10 days for immobilized and free ChOx were 97.68% and 36.25% of its initial activity, respectively. The immobilized enzyme also showed better thermal stability, with immobilized and free ChOx respectively retaining 88.35% and 58.05% of its initial activity after incubated at 70^oC.