Au-doped magnetic Fe₃O₄ nanoparticles were synthesized and used for fabrication of acetylcholinesterase (AChE) immobilized electrochemical sensor for the detection of organophosphorus pesticides (OP), such as dichlorvos. The degree of inhibition of the AChE enzyme by OP compounds was determined by measuring the electrooxidation current of the thiocholine generated by the AChE catalyzed hydrolysis of acetylthiocholine (ATCh). The use of these mixed nanoparticles was shown to provide both significant enzyme stabilization and low detection limit for the biosensor. A value of 10.3 mmol/L for the apparent Michaelis-Menten constant ( ) was obtained. The biosensor detected as low as 4.0×10^－13 mol/L dichlorvos.

Key words: Au-Fe₃O₄, acetylcholinesterase, organophosphorus pesticide, dichlorvos