A novel highly sensitive electrochemical biosensor for the direct determination of the reactive oxygen species superoxide, O 2•−, using superoxide dismutase has been developed, by incorporating multiwalled carbon nanotubes (MWCNT) together with the conducting polymer poly (3, 4-ethylenedioxythiophene)(PEDOT) in different configurations. After characterisation, the experimental conditions have been optimized and the analytical parameters of superoxide dismutase biosensors based on PEDOT/CNT or CNT/PEDOT modified glassy carbon electrodes, as well as those with one component only (MWCNT, PEDOT), have been determined. The biosensor with CNT on top of PEDOT presented the best analytical performance due to synergistic effects, with fast, and selective response to O 2•−, a high sensitivity of∼ 1115 μA cm− 2 mM− 1 and a low detection limit of 1 μM, and was applied to the determination of the antioxidant capacity of beverages. The biosensor exhibited outstanding stability over a period of 2 months, with a slight increase in the initial sensitivity.