Rapid time-resolved fluoroimmunoassay for diethylstilbestrol in cow milk samples with a highly luminescent Tb3+ chelate

Diethylstilbestrol (DES) is a non-steroidal synthetic molecule with estrogenic activity that provokes increased health risk in women whose mothers were given DES during pregnancy. In spite of this, it is sometimes illegally used as growth promoter in livestock breeding. Therefore methods that make it possible to monitor the presence of DES in food or in the environment might be of great interest. We describe a quantitative immunoassay with highly luminescent Tb3+ complex of 10-[4-(3-isothiocyanatopropoxy)benzoylmethyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (Tb3+ ⊂ 1) conjugated with a goat anti-rabbit IgG applied as marker in a time-resolved determination of DES. Lanthanide chelate is very stable and highly luminescent in aqueous solution, and makes it possible to reach the 0.5 μg L−1 sensitivity required in the control of illegal use of DES. DES recovery in milk samples was between 96% and 104.2%. The assay was performed using a rabbit polyclonal antibody specific to DES. This procedure can be applied directly to raw milk samples, and is useful as an alternative to conventional methods, providing a simple, on-site control for dairy farms.