2] Fluorescence excitation transfer immunoassay (FETI)

Abstract

This chapter discusses the different aspects of fluorescence excitation transfer immunoassay (FETI). Immunoassays have become the single most important tool for the determination of analytes in human body fluids. FETI has somewhat more demanding requirements for antibody specificity than heterogeneous immunoassay methods. The fluorescence enhancement produced upon antibody binding to fluorescein-iodothyronine conjugates is caused, by the relief of internal heavy atom-induced, quenching in the conjugate. A significant factor, in applying FETIs, generally, is the need to obtain pure labeled antigen. In order to avoid a large unmodulatable fluorescence background and loss of assay sensitivity, the labeled antigen must generally have greater than about 50% purity. The purity problem is exacerbated, by the apparent loss of fluorescent dyes, from relatively impure conjugates on storage in the solution. Two basic procedures are employed in FETIs. In the endpoint protocol, maximum utilization of the total modulatable signal, and hence maximum sensitivity is obtained. It is found that good correlations have been obtained, using patient serum samples, when FETI data were compared, with heterogeneous fluorescence immunoassay and radioimmunoassay procedures.