Immobilization of the enzyme is one of the most critical processes for the fabrication of an enzyme sensor, since it will highly influence properties of the obtained sensor. Various procedure have been proposed for a the preparation of glucose sensor, such as covalent attachment, cross-linking, hydrogel entrapment, polymer film entrapment, and the combination of two or more methods. Among the various techniques, the electrodeposition method is interesting owing to its simple preparation, miniaturization, and precise localization of enzyme.

On the other hand, nanocarbons (NCs), such as carbon nanotubes (CNTs) and graphenes, are extremely attractive in biosensor application, since they can combine properties of the high surface area, high stability and good electrical conductivity. However, NCs is not soluble in aqueous solution, which is the least media to dissolve enzyme without reducing its activity. The use of surfactants is a candidate to preparer a disperse NCs in enzyme solution, while this may also reduce the enzyme activity. Therefore, processes of enzyme immobilization and NCs immobilization are commonly performed separately using different solutions.

In this study, stable dispersed solutions of glucose oxidase (GOx) and multi-walled CNT were developed using gellan gum, which is a polysaccharide manufactured by microbial fermentation used widely as a gelling agents. By using this CNT/GOx dispersed solution, both CNT and GOx were successfully immobilized on Pt-Ir electrode by a simple step of applying a constant potential of 1.3 V（vs. Ag/AgCl) to the electrode in this solution. The electropolymerization of o-phenylenediamine was followed in order to increase the stability of enzyme-immobilized electrode. The CNT/GOx immobilized electrode performed as a glucose sensor with a high sensor sensitivity. This indicate that the introduction of CNT in GOx-immobilized film increased the efficiency of electron transfer between the electrode and generated hydrogen peroxide. In addition, the reproducibility of electrode fabrication was satisfactorily improved by the use of gellan gum compared with that using Triton X-100 as a dispersing agent.