An amperometric acetylcholinesterase sensor based on Fe3O4 nanoparticle/multi-walled carbon nanotube-modified ITO-coated glass plate for the detection of pesticides

A method is described for the construction of a highly sensitive electrochemical biosensor for the detection of malathion, chlorpyrifos, monocrotophos and endosulfan based on covalent immobilization of acetylcholinesterase (AChE) on iron oxide nanoparticles (Fe3O4NPs)-decorated carboxylated multi-walled carbon nanotubes (c-MWCNTs) electrodeposited onto indium tin oxide (ITO)-coated glass plate. Transmission electron microscopic (TEM) and UV analysis of nanocomposite materials demonstrated that Fe3O4NPs were well deposited on the outer walls of c-MWCNTs. The modified electrode was characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The resulting biosensor exhibited a linear response for acetylthiocholine in a concentration range of 0.1–700 μmol L−1 with a remarkable sensitivity of 0.402 mA/μmol L−1. Under optimum conditions, the inhibition rates of pesticides were proportional to their concentrations in the range of 0.1–70 nmol L−1, 0.1–50 nmol L−1, 0.1–70 nmol L−1 and 0.1–100 nmol L−1 for malathion, chlorpyrifos, monocrotophos and endosulfan, respectively. The detection limit of the biosensor for all pesticides was 0.1 nmol L−1 at a signal-to-noise ratio of 3. The biosensor showed good reproducibility, no interference by metal ions and long-term stability. The measurement results obtained by the present biosensor were in good agreement with those obtained by the standard gas chromatography–mass spectrometry method. The biosensor was employed for the determination of pesticides in environmental and food samples.

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► Constructed AChE biosensor based on AChE/Fe3O4NPs/c-MWCNT/ITO electrode.
► Enzyme electrode was characterized by AFM, FTIR, CV and EIS.
► Detection limit and working range of biosensor were 0.1 nM and 0.1–100 nM.
► Half life of enzyme electrode was 3 months.
► Biosensor measured pesticides in environmental and food samples.