title: Sensitive detection of organophosphorus pesticides using a needle type amperometric acetylcholinesterase-based bioelectrode. Thiocholine electrochemistry and immobilised enzyme inhibition.
abstract: An acetylcholinesterase (AChE) based amperometric bioelectrode for a selective detection of low concentrations of organophosphorus pesticides has been developed. The amperometric needle type bioelectrode consists of a bare cavity in a PTFE isolated Pt-Ir wire, where the AChE was entrapped into a photopolymerised polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ). Cyclic voltammetry, performed at Pt and AChE/Pt disk electrodes, confirmed the irreversible, monoelectronic thiocholine oxidation process and showed that a working potential of +0.410 V vs. Ag/AgCl, KCl(sat) was suitable for a selective and sensitive amperometric detection of thiocholine. The acetylthiocholine detection under enzyme kinetic control was found in the range of 0.01-0.3 U cm(-2) of immobilised AChE. The detection limit, calculated for an inhibition ratio of 10%, was found to reach 5 microM for dipterex and 0.4 microM for paraoxon. A kinetic analysis of the AChE-pesticide interaction process using Hanes-Woolf or Lineweaver-Burk linearisations and secondary plots allowed identification of the immobilised enzyme inhibition process as a mixed one (non/uncompetitive) for both dipterex and paraoxon. The deviation from classical Michaelis Menten kinetics induced from the studied pesticides was evaluated using Hill plots.
authors.affiliation: Department of Physical Chemistry, Babes-Bolyai University, Cluj-Napoca, Romania. gturdean@chem.ubbcluj.ro
authors.forename: Graziella L
authors.initials: GL
authors.lastname: Turdean
authors.forename: Ionel Catalin
authors.initials: IC
authors.lastname: Popescu
authors.forename: Liviu
authors.initials: L
authors.lastname: Oniciu
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Thevenot
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D004566:Electrodes; D004593:Electrophorus; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D004800:Enzymes, Immobilized / Q000037:antagonists & inhibitors*; D007306:Insecticides / Q000737:chemistry / Q000494:pharmacology*; D007700:Kinetics; D010261:Paraoxon / Q000032:analysis / Q000494:pharmacology; D012680:Sensitivity and Specificity; D013860:Thiocholine / Q000737:chemistry*; D014236:Trichlorfon / Q000032:analysis / Q000494:pharmacology
chemical_list: D002800:Cholinesterase Inhibitors; D004791:Enzyme Inhibitors; D004800:Enzymes, Immobilized; D007306:Insecticides; D013860:Thiocholine; D014236:Trichlorfon; D000110:Acetylcholinesterase; D010261:Paraoxon