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An enzyme-based biofuel cell with a pH-switchable oxygen electrode, controlled by enzyme logic operations processing in situ biochemical input signals, has been developed, Fig. 1. 1 Enzyme-based logic gates (AND/OR) and complex combination of several concatenated logic gates (logic network) were assembled to process biochemical signals and to convert them logically into pH-changes of the solution. The cathode used in the biofuel cell was modified with a polymer-brush functionalized with Os-complex redox species operating as relay units to mediate electron transport between the conductive support and soluble laccase biocatalyzing oxygen reduction. The electrochemical activity of the modified electrode was switchable by alteration of the solution pH value. The electrode was electrochemically mute at pH> 5.5 and it was activated for the bioelectrocatalytic oxygen reduction at pH< 4.5. The sharp …