BIOSENSORS Extraction and Detection of Pesticides by Cholinesterase Inhibition in a Two-Phase System: a Strategy to Avoid Heavy Metal Interference

A novel method of extraction has been developed to avoid the presence of heavy metals during the measurement of pesticides based on acetylcholinesterase (AchE) inhibition. Heavy metals have been in fact demonstrated in this article to interfere when the assay is performed by using the classic spectrophotometric Ellman’s method. We present the results obtained with an assay system using two different phases, one organic and the other aqueous, in which the pesticide and the enzyme are, respectively, solubilized. In a first step, the concentration of the substrate acetylthiocholine (1 mM), of the enzyme (7 mU mL), and the reaction time (20 min) for measurement of enzyme activity were optimized in aqueous solution. Next, the effect of an organic phase on the enzyme activity was studied by the addition of various solvents with the activity being evaluated after 10 min of mixing. It was found that by using hexane, the enzyme retained almost 100% of its Received 18 April 2005; accepted 15 May 2005 The authors thank the MIUR project FISR-1999 and the EU project BIOCOP for