Nanostructured bioelectrodes were designed and assembled into a biofuel cell with no separating membrane. The glassy carbon electrodes were modified with mediator-functionalized carbon nanotubes. Ferrocene (Fc) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) bound chemically to the carbon nanotubes were found useful as mediators of the enzyme catalyzed electrode processes. Glucose oxidase from Aspergillus niger AM-11 and laccase from Cerrena unicolor C-139 were incorporated in a liquid-crystalline matrix-monoolein cubic phase. The carbon nanotubes-nanostructured electrode surface was covered with the cubic phase film containing the enzyme and acted as the catalytic surface for the oxidation of glucose and reduction of oxygen. Thanks to the mediating role of derivatized nanotubes the catalysis was almost ten times more efficient than on the GCE electrodes: catalytic current of glucose oxidation was 1 mA cm(-2) and oxygen reduction current exceeded 0.6 mA cm(-2). The open circuit voltage of the biofuel cell was 0.43 V. Application of carbon nanotubes increased the maximum power output of the constructed biofuel cell to 100 μW cm(-2) without stirring of the solution which was ca. 100 times more efficient than using the same bioelectrodes without nanotubes on the electrode surface.

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Glassy carbon electrodes modified with films composed of a network of single-wall carbon nanotubes (SWCNTs) and liquid-crystalline cubic phase were used for dioxygen reduction catalyzed by laccase. In the presence of pristine SWCNTs, the overpotential of dioxygen reduction was decreased by 0.5 V (E 1/2 ¼ À 0.09 V). Adding laccase to the system shifted the potential of oxygen reduction to þ 0.52 V vs. Ag/AgCl reference electrode. Carbon nanotubes increased the electrode working area and improved the conductivity of the film. The current density of oxygen reduction was further enhanced by using a common mediator, 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS). Two procedures for modifying carbon nanotubes with ABTS were compared: by adsorption and by covalent binding. Covalent binding of ABTS to the nanotubes is advantageous since it completely eliminates leaching of mediator to the solution and leads to a stable biocathode system.

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