Increased paraoxon detection with solvents using acetylcholinesterase inactivation measured with a choline oxidase biosensor

Inactivation by paraoxon of free and immobilized acetylcholinesterase, in the presence of various amounts of different organic solvents, and with choline oxidase immobilized on an oxygen electrode was studied. With acetylcholinesterase in solution it was found that 5% cyclohexane enhances paraoxon detection when compared to the detection without solvent. In these conditions, as low as 10(-9) M paraoxon can be detected. Free acetylcholinesterase was more sensitive to paraoxon than immobilized acetylcholinesterase, depending on the nature and concentration of solvent (500-fold in the presence of 5% cyclohexane). The stability of the biosensor in continuous use and stored at room temperature was at least 3-4 weeks with triton X100 and bovine serum albumin addition. The sensitivity of paraoxon detection with free acetylcholinesterase in the presence of 5% cyclohexane corresponds to 0.2 ppb paraoxon, 10-fold below the legal limit admitted in the European Economic Community. The same approach could be applied for detection of low amounts of different organophosphorus or carbamate pesticides. (C) 1996 Elsevier Science Limited