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Carbon paper covered with side-naphthylated multi-walled carbon nanotubes was used as the conducting support for the construction of a biocathode in a hybrid biofuel cell (biobattery). Laccase Cerrena unicolor enzyme was employed as the catalyst for the 4e reduction of oxygen and a zinc disc covered with hopeite was used as the anode. Derivatized carbon nanotubes increase the working surface of the electrode and provide direct contact with the active sites of laccase. Biobattery characteristics under externally applied resistance, and power-time dependencies under flow cell conditions were evaluated. The system including the sandwich biobattery powering a dedicated two-electrode minipotentiostat with a simple sensor electrode was employed for monitoring a model neurotransmitter-catechol. The biobattery-powered sensor yielded the oxidation currents linearly dependent on catechol concentration in the range 0-2 mM and with a correlation coefficient of 0.998. This type of biobattery with laccase as the cathode catalyst can be integrated with analytical devices and power them even in long-time monitoring experiments. Biofuel cells (BFC) and hybrid biofuel cells (biobatteries) have several advantages over conventional fuel cells, e.g. they use enzymesvery efficient catalysts to transform chemical energy to electrical energy. The attractiveness of biofuel cells is due to possibilities of variety of applications of high energy density biofuels such as ethanol, glycerol and carbohydrates, work at room temperatures, at pH close to neutral and the products of reactions are environmentally-friendly. [1][2][3][4] Enzymes are also less expensive than metallic catalysts used in conventional fuel cells and additionally are specific and selective, therefore do not require membrane separating electrode compartments. The biofuel cell can work as open-type device, and can be easily miniaturized. 4 Initial market opportunities for biofuel cells are likely to be where there is a need for large amounts of energy but low power demands. This is because biofuel cells can achieve high efficiencies for oxidizing a given fuel, providing high energy density, but have lower power densities due to lower catalytic activity compared to metal catalyst based fuel cells.3 An important area of applications of the biofuel cells is powering electronic devices, e.g. clocks, timers or toys, small medical devices such as biosensors and drug delivery systems. 5-9The number of enzyme molecules that can be directly bound to the conductive support is rather low, due to their large size leading to small surface concentration of catalytic active sites per electrode geometric area. Therefore application of a three dimensional conductive matrix is required. Carbon nanotubes increase the working surface area of the electrode and improve conductivity of the film. Furthermore, carbon nanotubes modified with different aryl groups provide easier access to the enzyme active sites and allow working in the direct electron transfer regime without any mediators. [10][11][...

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