A key aspect of this design is that the sensing electrode is placed at the end of a channel long enough (> 4 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 9 seconds after introduction into the capillary channel when using paraformaldehyde, and 1.1 seconds when using ethanol (Figure and Figure ). Simulations of the O2 and paraformaldehyde concentration profiles within the capillary for a typical sensing duration in the coulometric mode (about 10 mins), predict that O2 penetrates less than 0.5 mm into the capillary ensuring that glucose sensing occurs under local anaerobic conditions at the sensing electrode. The simulations also predict that it would take 0.54 days (or 0.95 days when using 50 mM EtOH as the reducing agent) for O2 entering through the capillary opening to deplete the reducing agent and reach the sensing electrodes. These time scales far exceed the typical sensing duration of single-use electrochemical biosensors, making this sensor and scavenger design compatible with virtually any point-of-use sensing application (Figure Simulations of the O2 concentration and formaldehyde concentration within the capillary channel when using paraformaldehyde as reducing agent after 9 s (time needed for depleted for the O2 initially dissolved in the sample), after 10 mins (time used for the coulometric measurements), and after 0.54 days (time needed for O2 to reach the sensing electrode). The grey dash line shows the position of the sensing electrode. The simulations account for the continuous supply of O2 through the capillary opening exposed to ambient air. The parameter values for the simulation are given in Table .