Quantum dot immobilized acetylcholinesterase for the determination of organophosphate pesticides using graphene-chitosan nanocomposite modified electrode

We have fabricated a sensitive acetylcholinesterase biosensor that is based on dual-signal amplification. A large amount of enzyme was immobilized on a glassy carbon electrode via specific binding between functionalized ZnSe quantum dots and acetylcholinesterase, and a graphene–chitosan nanocomposite was introduced that improves the response. These two factors render the biosensor highly sensitive to acetylthiocholine chloride. Organophosphate pesticides were detected with this biosensor using methyl parathion as a model enzyme inhibitor. Under optimal conditions, there is a linear relationship between the percentage of inhibition (I%) and the log of the concentration of methyl parathion in the 0.5 nM to 0.5 μM range, with a 0.2 nM detection limit (at an S/N of 3). The biosensor displays acceptable reproducibility and relatively good storage stability. It was successfully employed to the determination of methyl parathion in spiked water and soil samples.