Fluorescein-labeled estradiol: a probe for anti-estradiol antibody.

A fluorescent estradiol derivative binds strongly to antiestradiol antibody. The binding, measured by fluorescence polarization, is inhibited by estradiol and by diethylstilbestrol. Tentatively characterized as N-(estradiol-6-iminooxyacetyl) fluorescein amine, the derivative was prepared from estradiol-6-iminooxyacetic acid, dicyclohexylcarbodiimide, and fluorescein amine, and isolated by TLC. It has a fluorescence emission similar to that of fluorescein and an absorption spectrum consistent with a fluorescein: estradiol molar ratio of 1:1.