A key aspect of this design is that the sensing electrode is placed at the end of a channel long enough (> 5 mm) to ensure that O2 is fully reduced by the O2-scavenger system before it can diffuse from the capillary openings to the sensing electrode. Simulations of the O2 scavenging process (Supplementary Information) predict that O2 within the sample is completely depleted 6.5 seconds after introduction into the capillary channel when using paraformaldehyde, and 0.8 seconds when using ethanol (Figure and Figure ). Simulation of the O2 and paraformaldehyde concentration gradients within the capillary over time predict that it would take 3.2 days (or 1.2 days when using 50 mM EtOH as the reducing agent) for O2 entering through the capillary opening to reach the sensing electrodes. For a typical sensing duration in the coulometric mode (10 mins), O2 only penetrates 0.5 mm into the capillary ensuring that glucose sensing occurs under local anaerobic conditions at the sensing electrode (Figure and Figure ).