In our first report we showed that dissolved O-2 could be reduced on osmium-based redox polymers with formal potential E degrees' <= + 0.07 V vs. Ag/AgCl. Here, we study the effect of O-2 on the calibration curves of the whole biosensors, i.e. comprising the redox polymer and the enzyme. A combination of electrodes were made with glucose oxidase (GOx) or quinoprotein-glucose dehydrogenase (PQQ-GDH), each with a redox polymer either sensitive or insensitive to O-2. These electrodes were studied under aerobic and anaerobic conditions. By combining amperometric and hydrodynamic experiments with loading studies, we found that for GOx-based electrode the effect of O-2 was maximal at a low glucose concentration where O-2 can be reduced by GOx and the osmium complex in the whole hydrogel volume, while O-2 is severely depleted in the outer layers at high glucose concentration. Further, no significant O-2 depletion was observed for electrodes modified with PQQ-GDH and O-2 sensitive polymer. In this case, the higher impact of O-2 at low glucose concentration could be explained by the longer average distance the electrons need to cover across-the O-2-rich hydrogel to reach the electrode. (C) 2013 Elsevier Ltd. All rights reserved.