Homogeneous Electrochemical Immunoassay Square Wave Voltammetry

2 Homogeneous Electrochemical Immunoassay (Square Wave Voltammetry) 

The principle of this competitive immunoassay without separation, developed by Degrand and Limoges, is based on electrochemical detection of a cationic electroactive label, a cobaltocenium salt and on the specific properties of Nafion , a polyanionic perfluorosulfonate possessing a strong affinity for small-sized cationic organic molecules. Its effect is to sort the molecules within a mixture according to their size and charge [48]. 

In the case of an immunoassay (Fig. 8.13) only the free fraction of the cationic tracers is extracted from the mixture and accumulates at the surface of the electrode where it is detected electrochemically. The antibody-cationic tracer complexes are too large to penetrate the polymer and are thus not detected. This is an elegant approach to the separation of free and bound fractions of tracers, permitting a homogeneous-phase like immunoassay. 

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