In this paper, a facile electrodeposition method without any additive has been successfully adopted to fabricate dendritic gold nanostructure (DenAu) on glassy carbon (GC) electrode and the prepared DenAu/GC electrode has large surface area. A sensitive third-generation superoxide radical (O-2(.-)) biosensor was then constructed by assembled L-cysteine (cys) onto the DenAu/GC electrode to immobilize large amounts of superoxide dismutase (SOD). The direct electron transfer of SOD was successfully realized and a pair of quasi-reversible redox peaks of SOD was observed at the SOD/cys/DenAu/GC electrode in the phosphate buffer solution (25 mM, pH 7.2). Due to the high loading of SOD on the electrode, the resulted biosensor exhibited good analytical performance for O-2(.-) detection, such as a low detection limit of 2.1 nM, a good stability and reproducibility, especially a wide linear range up to 540 mu M. (C) 2014 Elsevier B.V. All rights reserved.