Response of Enzyme-Based Biosensors

The theoretical description of the response of enzyme-based biosensors assumes that within the enzyme layer, steady-state concentrations of substrates and products 

Once substrate has arrived in the reaction layer, simple one-substrate Michaelis-Menten kinetics (Eq. 7.5 for oxidoreductase enzymes, where Eo and Er represent oxidized and reduced enzyme, respectively) yield fluxes for the formation of the enzyme-substrate complex O c) and the decomposition of this complex to form product (/p), Eqs. 7.6 and 7.7  

These fluxes are simply the homogeneous reaction rates multiplied by the thickness of the enzymatic reaction layer, as given in Eq. 7.1. 

For amperometric transducers, it is the regeneration of Eo by reaction with an oxidant (O2 or another mediating species M2+) that results in the species actually measured by the transducer. This reaction, Eq. 7.8, results in a flux for the regeneration of Er given by Eq. 7.9  

Recalling that at all distances from the transducer surface, the total enzyme concentration is equal to the sum of the concentrations of the three enzyme species ([E]T = [Eo] + [ES] + [Er]), and setting j = js = jc = jp = Je (as a direct result of the steady-state assumption), the flux j is described by Eq. 7.10  

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