An Os hydrogel based on the covalent attachment of Os(byp)(2) ClPyCHO to PAA-NH2 was cross-linked with glucose oxidase (GOx), lactate oxidase (LOx) and horseradish peroxidase (HRP) on GC and Au electrodes by PEG-400 bifunctional reagent. Single layer monoenzyme (GOx or LOx) and bienzyme (HRP-GOx) single layer modified electrodes were prepared with the Os moieties acting as "electron wires or electron shuttles". Cyclic voltammetry showed diffusional charge propagation in the gel which resulted more stable than similar ferrocene based gels reported before. In solutions containing the substrates, catalytic currents were obtained due to enzyme catalysis for the oxidation of glucose and lactate by the respective enzymes mediated by the Os polymer either by detecting directly the anodic current in a single enzyme electrode or indirectly by further reducing the peroxide formed in the aerobic enzymatic cycle at the Os-wired HRP. A rotating disc electrode (RDE) and a wall jet electrode (WJE) were employed as hydrodynamic electrodes in order to correct the amperometric response for substrate concentration polarization in the external electrolyte.