A rapid and sensitive time-resolved fluoroimmunoassay (TR-FIA) based on the biotin-streptavidin amplification system was developed for the determination of diethylstilbestrol (DES). Europium-labelled streptavidin derivatives combined with europium and anhydride of diethylene triamine penta-acetic acid were used to label streptavidin; biotin was coupled with goat anti-rabbit IgG to form a biotin-goat anti-rabbit IgG bridge between streptavidin-europium and the anti-DES antibody in the immunoassay. The DES assay was carried out by measuring the fluorescence of Eu(3+) -SA at 615 nm. The presented method produced a wide linear range, 0.001-1000.0 ng/mL, and a detection limit up to 0.81 pg/mL for DES. The method was applied to determine DES in serum samples, with recoveries of 97.4-107.8% and RSD 1.32-4.04%. The assay results by the present method showed that biotin-streptavidin amplified TR-FIA for DES detection; it may offer high sensitivity and promising alternative special methods in biological samples.
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