Acetylcholinesterase biosensor design based on carbon nanotube-encapsulated polypyrrole and polyaniline copolymer for amperometric detection of organophosphates

A simple method to immobilize acetylcholinesterase (AChE) on polypyrrole (PPy) and polyaniline (PANI) copolymer doped with multi-walled carbon nanotubes (MWCNTs) was proposed. The synthesized PAn-PPy-MWCNTs copolymer presented a porous and homogeneous morphology which provided an ideal size to entrap enzyme molecules. Due to the biocompatible microenvironment provided by the copolymer network, the obtained composite was devised for AChE attachment, resulting in a stable AChE biosensor for screening of organophosphates (OPs) exposure. MWCNTs promoted electron-transfer reactions at a lower potential and catalyzed the electro-oxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of OPs on the AChE activity, using malathion as a model compound, the inhibition of malathion was proportional to its concentration ranging from 0.01 to 0.5 μg/mL and from 1 to 25 μg/mL, with a detection limit of 1.0 ng/mL. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors.