We are interested in investigating the applications of biocatalytic mediated reduction of oxygen by oxygenases in films on electrode surfaces, as such reactions can form the basis for biosensors or biocatalytic fuel cell development. Here we present approaches aimed at improving the stability and signal output of such films. These include selection of oxygen reducing biocatalysts which are active under physiological conditions and development of redox mediators which offer the opportunity to tailor the mediator to each enzyme. It was found that for each enzyme Melanocarpus albomyces laccase (MaL), Trametes hirsutus laccase (ThL) or bilirubin oxidase (MvBOD) it was the biocatalytic films mediated by Os(2,2'-bipyridine)(2)Cl center dot PVI that not only generated the highest current densities compared to Os(4,4'-dimethyl-2,2'-bipyridine)(2)Cl center dot PVI and Os(4,4'-dichloro-2,2'-bipyridine)(2)Cl center dot PVI. but also proved to be the most stable over 48 h. Under physiological conditions electrodes constructed from MvBOD generated the highest initial current densities for each of the osmium redox polymers, however these films proved to be the least stable over 48 h. Stability could be improved using surface pre-treatment. (C) 2009 Elsevier B.V. All rights reserved.