Direct solid-phase time-resolved immunofluorometric assay of cortisol in serum

A dissociation-enhanced lanthanide fluoroimmunoassay of serum cortisol based on time-resolved fluorescence is described. The assay is a direct assay, where cortisol immobilized on the wall of a microtiter-strip well competes with cortisol in the sample for the europium-labeled polyclonal antibody. The amount of bound europium-labeled antibody is inversely proportional to the amount of cortisol in the sample. Separation is accomplished by washing the strip well. The assay is carried out in 2 h, at room temperature; it is easy to perform and gives accurate and reliable results. A chaotropic agent, trichloracetic acid, was very effective in releasing cortisol from binding proteins. This finding will have practical importance in the immunoassay field.