REUSABLE FIBER OPTIC IMMUNOSENSOR FOR RAPID DETECTION OF IMAZETHAPYR HERBICIDE

Imazethapyr is the active ingredient of PURSUIT herbicide. This herbic ide belongs to the imidazolinone class of compounds. Polyclonal antibo dies have been prepared in rabbits and sheep which specifically recogn ize this class of compounds. Using immune sera, ELISAs have been devel oped for imazaquin, imazapyr, imazethapyr, and imazmethabenz methyl (t he active ingredient for SCEPTER, ARSENAL, PURSUIT, and ASSERT herbici des, respectively) with sensitivity at low nanogram per milliliter lev els. The quantitation of imidazolinones in soil requires a certain amo unt of sample pretreatment, thus, the throughput is not ideal. A simpl er immunoassay method for screening large amounts of soil samples econ omically would be useful. Using the same polyclonal antibody, fluoresc ent immunoassay employing optical fiber and fluorescence (Block, M. J. ; Hirschfeld, T. B. U.S. Patent 4,582,809, 1986) was developed to assa y for imazethapyr. Purified sheep antibody was immobilized on quartz f ibers. A mixture of fluorescein-labeled imazethapyr analog and free im azethapyr was presented to the fiber for direct competition of the ant ibody binding sites or displacement of a previously bound fluoresceina ted imazethapyr analog on the surface of the fiber. The response time for the detection of imazethapyr ranged from seconds to minutes. The s ensitivity of the assay was 1 nM (0.3 ng/mL). This binding of the fluo rochrome to the fiber was reversible by washing with a phosphate buffe r saline. Multiple measurements were easily processed with a single fi ber over the course of several hours. Analysis of imazethapyr residue in soil can be accomplished by subjecting a clarified soil extract sol ution directly for analysis without further treatment. The cross-react ivity data indicated that the assay is apparently specific for the imi dazolinone class of compounds.