Immobilization of acetylcholinesterase based on the controllable adsorption of carbon nanotubes onto an alkanethiol monolayer for carbaryl sensing

Abstract

A simple method to immobilize acetylcholinesterase (AChE) on the controllable adsorption of multiwalled carbon nanotubes (MWCNTs) onto an alkanethiol self-assembled monolayer (C₆H₁₃SH SAM) modified Au electrode was proposed. The surface coverage of the MWCNTs was readily controlled by adjusting the immersion time for the adsorption of the MWCNTs. Atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to monitor these controllable fabrication processes. The MWCNTs adsorbed onto the SAM surface substantially restores the heterogeneous electron transfer between the bare Au electrode and the redox system in the solution phase that is almost totally blocked by the SAM of C₆H₁₃SH, and as a result, the prepared MWCNT-SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. Due to the inherent conductive properties of MWCNTs, the immobilized AChE exhibited high affinity to its substrate and produced a detectable and fast response. Thus, a sensitive, efficient and stable amperometric sensor for quantitative determination of carbaryl was developed. The inhibition of carbaryl was proportional to its concentration ranging from 0.001 to 1 μg mL⁻¹ and 2 to 15 μg mL⁻¹, with a detection limit of 0.6 ng mL⁻¹. The determination of carbaryl in garlic samples showed acceptable accuracy, which provided a new promising tool for analysis of enzyme inhibitors.