A POTENTIOMETRIC MICROBIAL BIOSENSOR FOR DIRECT DETERMINATION OF ORGANOPHOSPHATE NERVE AGENTS

An easy to construct and inexpensive potentiometric microbial biosenso r for the direct measurement of organophosphate (OP) nerve agents was developed. The biological sensing element of this biosensor was recomb inant Escherichia coil cells containing the plasmid pJK33 that express ed organophosphorus hydrolase (OPH) intracellularly. The cells were im mobilized by entrapment behind a microporus polycarbonate membrane on the top of the hydrogen ion sensing glass membrane pH electrode. OPH c atalyzes the hydrolysis of organophosphorus pesticides to release prot ons, the concentration of which is proportional to the amount of hydro lyzed substrate. The sensor signal and response time were optimized wi th respect to the buffer pH, ionic concentration of buffer and tempera ture. using paraoxon as substrate. The best sensitivity and response t ime were obtained using a sensor operating in pH 8.5, 1 mM HEPES buffe r and 37 degrees C. The biosensor was applied for measurement of parao xon, ethyl parathion, methyl parathion and diazinon.