Amperometric measurement of organophosphate pesticides using a screen-printed disposable sensor and biosensor based on cobalt phthalocyanine
A screen-printed carbon electrode, impregnated with the electrocatalyst cobalt phthalocyanine (CoPC), was used in conjunction with the enzyme acetylcholinesterase (AChE) for the amperometric determination of organophosphate pesticides (OPs). Firstly the enzyme was investigated in free solution and then immobilized onto the electrode surface using a glutaraldehyde solution.
Acetylthiocholine (ATCh) was employed as the substrate for the production of thiocholine, the latter being monitored at an applied potential of +0.1 V versus SCE. After incubating AChE at 37 °C for 10 min with paraoxon or dichlorvos, a decrease in the signal occurred due to the inactivation of the enzyme by these pesticides. The percentage inhibition was found to be related to the logarithm of the pesticide concentration; paraoxon and dichlorvos could be detected down to 4.95 × 10–8 and 5.9 × 10–8 mol l–1, respectively. With immobilized enzyme, these pesticides could be detected down to 6.5 × 10–7 and 1.7 × 10–6 mol l–1, respectively.
The method involving enzyme in free solution was also applied to two sulfur-containing organophosphate pesticides, namely, malathion and parathion. The former could be detected down to 4.07 × 10–8 mol l–1 when the incubation time was increased to 30 min; an active form might have been produced during the incubation period. Parathion did not cause enzyme inactivation under the same conditions as malathion. It was necessary to leave parathion in buffer pH 8.0 for a prolonged period to form an active derivative which inhibited the enzyme to various degrees, depending on the pre-incubation time.