Microbial and cytoplasmic membrane-based potentiometric biosensors for direct determination of organophosphorus insecticides

Potentiometric biosensors for the determination of organophosphorus (OP) in secticides were developed by applying either immobilized whole cells or cyt oplasmic membrane fractions of wild-type Flavobacterium sp. on the surface of a glass pH electrode. The ability of Flavobacterium sp. to degrade OP co mpounds as sole carbon source was demonstrated for parathion with a degrada tion rate of almost 100% after 30 min and for chlorpyrifos of 33% after 48 h incubation. The products of hydrolysis of these compounds, p-nitrophenol and 3,5,6-trichloro-2-pyridinol, were accumulated in the medium and not use d as substrates for growth by Flavobacterium sp. In the course of hydrolysi s, which is catalyzed by organophosphorus hydrolase, two protons are releas ed for each substrate molecule hydrolyzed. This stoichiometry forms the ele ctrochemical basis of the potentiometric biosensors. Direct determination w ithout previous extraction of OP was carried out in a stirred measuring cel l with a pH electrode as transducer. Poly(carbamoyl sulfonate) (PCS) prepol ymer. a hydrogel with good adhesive properties, was used for immobilization of whole cells and membrane-associated organophosphorus hydrolase. The sen sor with cytoplasmic membrane fractions was superior to the one with whole cells and showed a linear range for paraoxon ti om 0.01 to 0.47 mM and 3 we eks' working stability.