Figure 2.

Electrochemical transduction modes of peroxidase-based biosensors. (a) In the direct approach, the reaction intermediates Compound I and II are directly reduced at the electrode at high potentials. The Fenton-type reaction route is initiated by conversion of the heme cofactor from the ferric (Fe³⁺) to the ferrous (Fe²⁺) state at lower potentials. (b) In the mediated approach, an additional compound is used to mediate electron transfer between working electrode and Compounds I and II. Peroxidase substrates can act similar to mediators when their products can be recycled at the electrode.