Electrochemically coupled enzymatic current

Coupling between a biologically catalyzed reaction and an electrochemical reaction, referred to as bioelectrocatalysis, is the constructional principle for enzyme-based electrochemical biosensors. This means that the flow of electrons from a donor through the enzyme to an acceptor must reach the electrode in order for the corresponding current to be detected. In case a direct electron transfer between the active site of an enzjane and an electrode is not possible, a small molecular redox active species, e.g. hydrophobic ferrocene, meldola blue and menadione as well as hydrophilic ferricyanide, can be used as an electron transfer mediator. This means that the electrons from the active site of the enzyme reduce the mediator molecule, which, in turn, can diffuse to the electrode, where it donates the electrons upon oxidation. When these mediator molecules are employed for coupling of an enzymatic redox reaction to an electrode at a constant potential, the resulting application can be referred to as mediated amperometry or mediated bioelectrocatalysis. 

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