Acetylcholinesterase biosensor based on self-assembled monolayer-modified gold-screen printed electrodes for organophosphorus insecticide detection

A mono-enzymatic acetylcholinesterase (AChE) amperometric biosensor for organophosphate detection was developed immobilizing the AChE enzyme via glutaraldehyde on a preformed cysteamine self-assembled monolayer (SAM) on gold-screen printed electrodes (Au-SPEs). The enzymatic activity was monitored measuring the enzymatic product, thiocholine, at an applied potential of +400 mV vs. Ag/AgCl using ferricyanide in solution as electrochemical mediator. The electrocatalytic activity of ferricyanide towards thiocholine was investigated by using Nicholson–Shain method and finding a second order homogenous rate constant ks equal to (5.26 ± 0.65) × 104 M−1 s−1. In order to develop a sensitive biosensor, the effect of cysteamine concentration, duration of SAM deposition and AChE concentration were optimized. Using paraoxon as model compound, the biosensor showed a linear range up to 40 ppb with a detection limit of 2 ppb (10% of inhibition). The biosensor was successfully challenged with drinking water sample demonstrating to be a useful analytical tool for organophosphorus insecticide detection.