How the reduction of O2 on enzymes and/or redox mediators affects the calibration curve of “wired” glucose oxidase and glucose dehydrogenase biosensors

In our first report we showed that dissolved O2 could be reduced on osmium-based redox polymers with formal potential E°′ ≤ + 0.07 V vs. Ag/AgCl. Here, we study the effect of O2 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 O2. 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 O2 was maximal at a low glucose concentration where O2 can be reduced by GOx and the osmium complex in the whole hydrogel volume, while O2 is severely depleted in the outer layers at high glucose concentration. Further, no significant O2 depletion was observed for electrodes modified with PQQ-GDH and O2 sensitive polymer. In this case, the higher impact of O2 at low glucose concentration could be explained by the longer average distance the electrons need to cover across the O2-rich hydrogel to reach the electrode.