Electrochemical thiocholine inhibition sensor based on biocatalytic growth of Au nanoparticles using chitosan as template

A simple strategy for the design of an electrochemical sensor based on enzyme-induced growth of gold nanoparticles (AuNPs) without adding gold nano-seeds was proposed with acetylcholinesterase (AChE) as a model. Owing to the excellent biocompatibility of chitosan film for the subsequent assembly of biological molecules, chitosan film was first electrochemically deposited on Au electrode surface from a mildly acidic chitosan solution via a negative voltage bias. Based on immobilization of AChE, a stable AChE sensor (AChE-CS/Au) was constructed. The immobilized AChE mediated hydrolysis of ATCl and yielded a reducing agent thiocholine. In the presence of AuCl4−, AuNPs were formed without addition of any metal nanoparticles. Atomic force microscopy (AFM) images proved that small spherical nanoparticles could grow on the enzyme-modified surface after incubation in HAuCl4 and ATCl solution. [Fe(CN)6]3−/4− redox system was used as a probe to indicate the process of electron transfer across the interface and also analyze the enzyme inhibitor quantitatively. The inhibition of malathion on AChE was proportional to its concentration in the range of 0.1–500 ng ml−1 (R = 0.9989), with detection limit of 0.03 ng ml−1.