Immumochromatographic assay for determination of hexoestrol residues

One-step membrane-based competitive colloidal gold-based immunoassays in lateral-flow formats for the rapid detection of hexoestrol (HES) were developed. Nitrocellulose membrane strip was separately coated with goat anti-rabbit IgG (control line) and HES hapten–OVA conjugate (test line). Anti-HES polyclonal antibody labelled with colloidal gold particles was firstly incubated with HES. A positive reaction as a result of the remaining antibody–gold conjugate combining with antigen coated on the membrane was obvious by visual detection, with detection limits for lateral flow of 10 μg/kg for detecting HES standard solution, and the limit of detection was 20 μg/kg for detecting the HES spiked in swine urine and liver. The assay time for test was less than 5 min, suitable for rapid testing on-site.