Application of chemisorption/desorption process of thiocholine for pesticide detection based on acetylcholinesterase biosensor

One-step electrochemical deposition of gold nanoparticles (AuNPs) in chitosan hydrogel onto a planar gold electrode was used to create a favorable surface for the attachment of the enzyme acetylcholinesterase (AChE). AChE exhibited high affinity to its substrate of acetylthiocholine chloride (ATCl) from calculated Michealis–Menten constant ( K m app ) of 0.309 mM. Thiocholine, the product through AChE-catalyzed hydrolysis of ATCl, could be chemisorbed on the surface with an applied potential of −0.7 V and then desorbed in KOH solution, giving a measurable peak current. When enzymatic activity was inhibited by organophosphate pesticides, the amount of chemisorpted thiocholine on the interface was anticipated to decrease. As a result, a simple method for rapid determination of malathion was established based on the chemisorption/desorption process of thiocholine used as an indicator. Under the optimal conditions, the decrease in response was proportional to the concentration of malathion from 0.1 to 20 ng mL−1, with detection limit of 0.03 ng mL−1 (0.1 nM). The method based on one-step electrochemical deposition and chemisorption/desorption process of thiocholin has potential application in high-sensitive pesticide determinations.