Study On Immunoassays For Methamidophos

With the increasing demand for the environment protection, food safety and human health, organophosphorus pesticides have attracted more and more attention. In this paper, different immunoassays for methamidophos were developed, including an ¹²⁵I radioimmunoassay, an ¹²⁵I coated tube radioimmunoassay, a direct competition ELISA, an ABC-ELISA, a dot enzyme filtration assay (DEFA), a dot immuno-gold filtration assay (DIGFA) and gold immunochromatographic assay (GICA) were developed.The antibody is the key reagent in immunoassays. In this paper, MTP-BSA and MTP-G-BSA were synthesized by EDC and two steps glutaraldehyde methods and polyclonal antibodies from New Zealand rabbits were obtained.The RIA has been widely used in quality and quantity clinical diagnostic for trace concentration of proteins, hormones, drugs and tumor markers in human fluids. In this paper, methamidophos-succinyl-histamine- ¹²⁵ I was synthesized to establishe a liquid phase radioimmunoassay for methamidophos. The sensitivity of the assay was 0.03nM and the C.V. was 5.2%. Then a coated tube solid phase radioimmunoassay for methamidophos was established. The sensitivity of the assay was 0.05nM and the C.V. is 7.8%.ELISA is the most widely used immunoassay in the pesticides residual analysis. In this paper, methamidophos-succinyl -HRP was synthesized and a direct competition ELISA for methamidophos (sensitivity =5nM and C.V. =12.6%) and an ABC-ELISA (sensitivity =1nM and C.V. =8.9%), which had a higher sensitivity, were established. Anti-methamidophos- IgG-HRP were also synthesized and a dot enzyme filtration assay on a NC membrane was established.A DIGFA ( dot immuno-gold filtration assay) is also developed for methamidophos. Colloidal gold is obtained by reducing the gold chloride with sodium citrate, and labeled anti-methamidophos affinity purified antibody. The methamidophos in the sample competes with the immobilized methamidophos-BSA conjugate in the test area for the limited colloidal gold-labeled antibody complex. The sensitivity is much lower than the RIA and ELISA.From the above experiments, it is concluded that the appropriate immunoassay method for the quantitative assay for methamidophos is ELISA, although it has lower sensitivity than RIA. After the instrument is widely in use, the CLIA and TRFIA will be the better choice. For the qualitative assay of methamidophos, the appropriate method is DIGFA at this moment. Only when the gold spry instrument is cheap enough, the GICA can become the practical pesticides residual analysis method because it has more advantages.