A disposable amperometric immunosensor for 2,4-dichlorophenoxyacetic acid

A disposable immunochemical biosensor for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was developed using a screen-printed electrode system as an amperometric transducer and monoclonal antibodies against 2,4-D as a biospecific part. At first, the electrochemical system for determination of peroxidase activity was studied. For measurements, the peroxidase substrates were hydrogen peroxide together with either hydroquinone, 1,2-phenylenediamine or pyrocatechol as electron donors, which were amperometrically detected using platinum, gold and graphite composite layers as working electrode materials. The optimal concentrations of reaction components were found, the highest signals being achieved for hydroquinone with gold or graphite electrodes. The immunochemical system makes use of the competitive assay principle with 2,4-D covalently immobilized either directly on the surface of the gold electrode or on a separate nylon membrane. The peroxidase-antibody conjugate was synthesized and used as a tracing reagent. By using 2,4-D immobilized through its carboxylic group directly to the silanized surface of the gold working electrode, a detection limit close to 0.1 μg/1 of free 2,4-D was achieved. One analysis was completed in 1 h (30 min for the immunochemical reaction, washing, 25 min incubation with substrate, measurement).