Biosensor for direct determination of organophosphate nerve agents. 1. Potentiometric enzyme electrode

A potentiometric enzyme electrode for the direct measurement of organophosp hate (OP) nerve agents was developed. The basic element of this enzyme elec trode was a pH electrode modified with an immobilized organophosphorus hydr olase (OPH) layer formed by cross-linking OPH with bovine serum albumin (BS A) and glutaraldehyde. OPH catalyses the hydrolysis of organophosphorus pes ticides to release protons, the concentration of which is proportional to t he amount of hydrolysed substrate. The sensor signal and response time was optimized with respect to the buffer pH, ionic concentration of buffer, tem perature, and units of OPH immobilized using paraoxon as substrate. The bes t sensitivity and response time were obtained using a sensor constructed wi th 500 IU of OPH and operating in pH 8.5, 1 mM HEPES buffer. Using these co nditions, the biosensor was used to measure as low as 2 mu M of paraoxon, e thyl parathion, methyl parathion and diazinon. The biosensor was completely stable for at least one month when stored in pH 8.5, 1 mM HEPES + 100 mM N aCl buffer at 4 degrees C. (C) 1999 Elsevier Science S.A. All rights reserv ed.