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An easy to construct and inexpensive potentiometric microbial biosensor for the direct measurement of organophosphate (OP) nerve agents was developed. The biological sensing element of this biosensor was recombinant Escherichia coli cells containing the plasmid pJK33 that expressed organophosphorus hydrolase (OPH) intracellularly. The cells were immobilized by entrapment behind a microporus polycarbonate membrane on the top of the hydrogen ion sensing glass membrane pH electrode. OPH catalyzes the hydrolysis of organophosphorus pesticides to release protons, the concentration of which is proportional to the amount of hydrolyzed substrate. The sensor signal and response time were optimized with respect to the buffer pH, ionic concentration of buffer and temperature, using paraoxon as substrate. The best sensitivity and response time were obtained using a sensor operating in pH 8.5, 1 mM HEPES buffer and 37 °C. The biosensor was applied for measurement of paraoxon, ethyl parathion, methyl parathion and diazinon.
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Mulchandani et al. (1998) studied this question.
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