Competitive immunochromatographic assay for the detection of the organophosphorus pesticide EPN

An immunochromatographic assay (ICA) based on competitive antigen-coated format and colloidal gold label was developed for the detection of the organophosphorus insecticide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN). The ICA test strip consisted of a membrane with a detection zone, a sample pad and an absorbent pad. The membrane was separately coated with EPN hapten-OVA conjugate (test line) and anti-mouse IgG (control line). As the competition is between the migrating analyte and the immobilised analyte hapten for the binding sites of the migrating antibody-colloidal gold (Ab-CG) conjugate, this study suggests that the relative migration speed between the two migrating substances is a critically important factor for the sensitive detection by competitive ICA. Based on this criterion, a nitrocellulose (NC) membrane was chosen as the most suitable for EPN ICA. The detection limit of the ICA for EPN standard and EPN spiked into agricultural samples were 10^-2 and 5×10^-2 μg mL^-1, respectively.