The possibility of interfering reactions between AOx and mediators was tested with the freely diffusing ferrocenedimethanol (Fc(MeOH)2) and with a polymer bound Os-complex (poly(1vinylimidazole)-Os(bpy)2Cl , Supplementary Information) that are classically used for electron mediation in oxidase-based biosensing (Figure and). Before addition of paraformaldehyde in the electrolyte containing AOx, catalase and Fc(MeOH)2, the CV displays the irreversible current wave for O2 reduction as well as the reversible currents due to Fc(MeOH)2 oxidation and reduction. After addition of paraformaldehyde, which completes the O2-scavenging system, the O2 reduction wave disappears while the current response for Fc(MeOH)2 remains unchanged (Figure ). In the case of the Os-complex modified polymers, before addition of paraformaldehyde into the electrolyte containing AOx and catalase, the CV also shows the O2 reduction peak and the redox peaks of the Os-complex (Figure ). After addition of paraformaldehyde, the O2 reduction peak disappears and the CV still only shows the reversible redox peaks of the Os-complex. The absence of catalytic current in these experiments with either Fc(MeOH)2 or the Os-complex modified polymers demonstrates the exclusive substrate specificity of AOx for O2 as the electron acceptor. This ensures that artificial electron mediators used in oxidase-based biosensors are not affected by the AOx-catalyzed O2removal.