An optical sensor for pesticide determination based on the autoindicating optical properties of peroxidase

During the enzymatic reaction of the heme-protein Horseradish peroxidase (HRP) with hydrogen peroxide there are changes in the molecular absorption spectra of HRP and its different oxidation states which can be used for quantitative determination of the substrate. One of these intermediate oxidation states is the HRPII, with iron as an oxyferryl. This compound is assumed to be responsible for the organophosphate pesticide degradation in the Fenton reaction. In this work, the enzymatic HRP–H2O2 reaction has been studied, based on the effect of different pesticides on the mechanism reaction; these modifications have been used for the quantitative determination of pesticides. A mathematical model has been developed relating to the analytical signal with the pesticide concentration. Three organophosphate pesticides (diazinon, trichlorfon and tetrachlorvinphos) and one sulfamide (dichlofluanid) have been used to demonstrate the viability of the methodology and the accomplishment fulfillment of the model. Tetrachlorvinphos was chosen as the pesticide model to develop the optical sensor film for continuous pesticide determination, consisting of HRP immobilized in a polyacrylamide gel. The sensor can be used for at least 15 days and responds linearly to tetrachlorvinphos concentrations in the range from 4.0×10−7 to 4.0×10−6 mol L−1. The main advantage of the methodology is its reversibility in contrast to the irreversible Fenton reaction. The HRP–H2O2 methodology has been used to measure the pesticides in a waste water sample spiked with tetrachlorvinphos.