Time-resolved fluoroimmunoassay of cortisol in serum with a europium chelate as label

A non-isotopic heterogeneous competitive immunoassay of serum cortisol is described. Cortisol present in the sample competes with immobilised cortisol (cortisol-thyroglobulin conjugate) for binding to a monoclonal anti-cortisol biotinylated antibody. The amount of antibody bound is measured on the dry solid-phase by time-resolved fluorometry after adding streptavidin labeled with the Eu3+ chelate 4,7-bis(chlorosulfophenyl)-1,10 phenanthroline-2,9-dicarboxylic acid (BCPDA), in the presence of excess Eu3+. The assay is simple to perform, its characteristics are similar to those of radioimmunoassay techniques, and is suitable for routine clinical use.