Evaluation of pesticide and heavy metal toxicity using immobilized enzyme alkaline phosphatase with an electrochemical biosensor

Abstract

An bioelectrochemical sensor or biosensor based on the inhibition of the enzyme Alkaline Phosphatase (ALP) has been investigated for the screening of several environmental toxicants. The biosensor was constructed by immobilizing ALP in a hybrid sol-gel/chitosan film that was deposited on the surface of a screen-printed carbon paste electrode (SPE). The inhibition was measured via the catalytic hydrolysis of ascorbic acid 2-phosphate (AA2P) by the enzyme to produce ascorbic acid, Oxidation of this product was monitored amperometrically and the current change was then related to ALP activity. Toxicity of herbicides (2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), insecticides (caxbofuran and α-endosulfan) and heavy metals (Hg2+, Cd2+, Ag2+, Zn2+ and Cu2+) towards the biosensor were evaluated. Various degrees of inhibition of ALP occurred when the biosensor was exposed to herbicides and heavy metals. This resulted in a lower acid ascorbic production by the enzyme from the substrate, thus a decrease in the current response of the biosensor. The herbicides 2,4-D and 2,4,5-T showed the largest inhibition effect on ALP with linear response range of 1-60 μg L-1 (R = 0.92). The maximum inhibitions caused by 2,4-D and 2,4,5-T were 46 and 30%, respectively. Heavy metals caused inhibition on ALP at the higher concentration range of mg L-1. Thus, the biosensor may be useful for the screening of chlorophenoxyacetic acid herbicides even in the presence of other environmental toxicants. © 2008 Academic Journals Inc.