The diversity and complexity of food matrix as well as the necessity for simple, sensitive and selective sensors encouraged us to develop the concept of "redox-flexible" modified carbon electrode containing several enzymes and mediators that can be efficiently used at different working potentials.

For amperometric biosensors the choice of the working potential is a real advantage as it permits to escape various interferences which are related manly to the complexity of the sample. Enabling the biosensors to work either on anodic or cathodic modes associated with the expansion of the working potential window increase the flexibility of the use of enzymatic biosensors in real samples.

In this lecture we will show how for oxidase enzymes based bio-assays and biosensors (glucose oxidase, lactate oxidase, NADH oxidase, cholesterol oxidase) the simultaneous association of horseradish peroxidase with a mediator, competitor or not with the natural co-substrate (O₂) of the enzyme permits to generate two different pathways for the analyte detection: one operating in anodic mode and the other in cathodic mode. The role of competitive reactions resulting from the association of different enzymes with the mediator will be also discuss.

The studies presented here were performed using disposable screen printed electrochemical cells with the carbon working electrode modified by the redox mediator and enzymes.

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