ELECTROCHEMICAL IMMUNOSENSORS FOR DETERMINATION OF THE PESTICIDES 2,4-DICHLOROPHENOXYACETIC AND 2,4,5-TRICHLOROPHENOXYACETIC ACIDS

Two immunochemical sensors are described for detection of the pesticid es 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyac etic acid (2,4,5-T). The assay monitors the competitive binding of fre e pesticide and pesticide-peroxidase conjugate with antibodies immobil ized on a graphite electrode, by measurement of peroxidase activity in the immune complexes on the electrode surface. 5-aminosalicyclic acid and H2O2 are used as substrates. An automated potentiometric device m easures changes in redox potential during the peroxidase reaction. The assay parameters were optimized to achieve detection limits of 40 ng/ ml 2,4-D and 50 ng/ml 2,4,5-T (in both water and serum). The total tim e required to perform the assay (including electrode regeneration) was 12 min, compared to about 2h for solid-phase enzyme immunoassays. The electrode life extends to 60 sequential measurements. The sensors the refore appear suitable for medical and ecological applications.