Two new redox-active osmium complexes of the type (Os(bpy)(2)Cl(pyX))(+) have been synthesised, where pyX corresponds to a pyridine derivative bearing a functional group (aldehyde, carboxylate). Their electrochemical behaviour and electronic spectra were studied in acetonitrile and aqueous solutions. The rate coefficients for the re-oxidation of glucose oxidase (GOx) by these new osmium complexes were obtained. The applicability to this system of the equation derived by Nicholson and Shain for an EC mechanism is discussed. The mediator containing the carbonyl group was bound to poly(allyl)amine. The new electroactive polymer was wired with oxidases in the construction of glucose and lactate sensors, as an example of the capabilities of these new osmium complexes to build integrated chemical systems.