Development of an ELISA for the detection of the residues of the insecticide imidacloprid in agricultural and environmental samples

A competitive enzyme-linked immunosorbent assay (ELISA) for the chloronicot inyl insecticide imidacloprid was developed using a polyclonal antibody pro duced against a hapten conjugated through the imidazolidine to keyhole limp et hemocyanin. In the standard curve of imidacloprid, an IC50 of 17.3 ng/mL was obtained using a competitive heterologous system at pH 10. Very low cr ossreactivity was found for some structurally related compounds including t he insecticide thiacloprid. The high cross-reactivity with a metabolite con taining the carbonyl group in the imidazolidine moiety suggests the involve ment of its polarity and stereochemical fitness in forming the antibody-ant igen complex. The effects of various assay conditions, including organic so lvents, detergent content, salt concentration, and pH on the sensitivity,we re evaluated. High-performance liquid chromatography was run for comparison to validate the ELISA with fortified water samples, the correlation being 0.997-0.998 (n = 15) with a slope of 1.10-1.38. The ELISA turned out to be a convenient tool for monitoring imidacloprid residues in agricultural and environmental samples.