An amperometric flow-through biosensor for the determination of pesticides is proposed. It is based on the inhibition of the acetyl cholinesterase-catalysed hydrolysis of 4-aminophenylacetate.
The calibration graphs were linear from 5.0 X lo-' to 1.0 x lop5 M and 5.0 X lo-' to 5.0 X lo-' M for paroxon and carbaryl, respectively. The detection limit (5% of inhibition) was 1.0 X lo-' M pesticide. The relative standard deviations (R.S.D.) (n = 5) were 3.7% for 4.0 X lop5 M and 4.0% for 8.0 X 10ph M for either carbaryl or paroxon. Electroactive species such as uric and ascorbic acid and benzafdehyde that could be oxidized at the same potential as 4-aminophenol, do not interfere. However, compounds which strongly absorb onto the electrode surface, such as bovine serum albumin (BSA) and surfactants capable of denaturing the enzyme activity, cause an interference. The stability of the sensor was high and even after repetitive use for one month the electrode retained 90% of its original activity. The determination of carbaryl and paroxon was carried out in lagoon water and kiwi fruits. The lowest concentration of pesticide determined in lagoon water was 1.0 X lo-' M for paroxon and 4.0 X lo-' M for carbaryl.