A Homogeneous Bioelectrochemical Immunoassay for Thyroxine

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Abstract
Thyroxine has been modified with a ferrocene derivative to produce an immunologically reactive conjugate which remains capable of functioning as an electron transfer mediator, shuttling electrons between an oxido-reductase enzyme and an electrode. On binding with an anti-thyroxine antibody the conjugate's ability to function as a mediator is impaired. The conjugate has been used as a tracer in an homogeneous competitive assay to quantify the total thyroxine concentration in serum, the assay being measured electro-chemically after the addition of a suitable oxidoreductase enzyme (glucose oxidase) and its substrate (glucose) on completion of antibody/antigen binding. This results in a simple and sensitive assay for thyroxine.