Heterogeneous fluoroimmunoassays using fluorescein as label with measurement of the fluorescence signal directly onto the solid-phase

A heterogeneous fluoroimmunoassay approach with measurement of the fluoresc ence signal directly onto the solid support is described. Fluorescein was e mployed as fluorescent label whereas plastic microtitration wells were used as solid carriers. The influence of the type of the plastic wells on the p roposed approach was investigated. Different types of commercially availabl e plastic microtitration wells (white-opaque, black, and transparent) were tested. The solid supports were judged on the grounds of the maximum fluore scence signal, the precision, and the sensitivity they provided in a model non-competitive assay for mouse IgG. Among the solid supports tested, the w hite-opaque wells provided the most promising results with respect to the p arameters in question. This support was also used for the development of a competitive fluoroimmunoassay for the determination of total thyroxin in hu man serum samples in order to assess the validity of the proposed approach under real immunoassay conditions. The assay developed had appropriate anal ytical characteristics for the determination of thyroxin and the serum samp le values obtained were well correlated with those determined by a commerci al solid-phase radioimmunoassay. (C) 1999 Elsevier Science B.V. All rights reserved.