CONDUCTOMETRIC BIOSENSORS BASED ON CHOLINESTERASES FOR SENSITIVE DETECTION OF PESTICIDES

Disposable conductometric microbiosensors based on immobilization of acetyl and butyrylcholinesterases (BuChEs) on interdigitated electrodes were fabricated. Enzymes were immobilized by crosslinking with bovine serum albumin and the differential output between the pair of electrodes covered with the enzyme membrane and the pair covered with albumin only was recorded. On the basis of these biosensors, a biochemical assay for pesticides in liquids was developed. Respective detection limits were 5 x 10(-11) M for diisopropyl fluorophosphate (DFP), 10(-7) M for trichlorfon, and 10(-6) M for paraoxon-methyl and paraoxon-ethyl for the assays based on the enzymes tested. The presence of pesticides in the sample in concentration exceeding the detection limits can be detected after only 10 minutes of incubation, whereas, in order to extend the range of the determined pesticide concentration and to improve the accuracy of the assay, it is better to use incubation times longer than 30 minutes. Use of pyridin-2-aldoximide methiodide as reactivating agent allowed one to achieve the complete recovery of the sensor response when it was incubated in low-concentrated pesticide solutions, e.g., less than 10(-6) M for paraoxon-methyl and during a short rime, e.g., 10 to 20 minutes, for 10(-5) M paraoxon-methyl solution.