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 (Kmapp) 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.