One-step synthesis of multiwalled carbon nanotubes-gold nanocomposites for fabricating amperometric acetylcholinesterase biosensor

A facile, one-step synthesis of nanocomposites using multiwalled carbon nanotube coating gold nanoparticles (MWCNTs-Au) was presented. Scanning electron microscopy and UV–vis spectroscopy confirmed that more than 97% of gold nanoparticles have been loaded on the surface of carbon nanotubes without congregation. The formed MWCNTs-Au nanocomposites offered an extremely hydrophilic surface for biomolecule adhesion, leading to a stable acetylcholinesterase (AChE) biosensor. Due to the excellent conductivity of the nanocomposites, the immobilized AChE showed favorable affinity to acetylthiocholine (ATCl) and could catalyze the hydrolysis of ATCl with a Kmapp value of 268 μM to form thiocholine, which was then oxidized to produce a detectable and fast response. Based on the inhibition of organophosphates (OPs) on the enzymatic activity of AChE, the magnitude of peak current from thiocholine on the biosensor is a simple and effective way to biomonitoring of OPs exposure. Using malathion as a model compound, the inhibition of malathion was proportional to its concentration ranging from 1.0 to 1000 ng mL−1 and from 2 to 15 μg mL−1, with a detection limit 0.6 ng mL−1. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors.