Molecular understanding of acetylcholinesterase adsorption on functionalized carbon nanotubes for enzymatic biosensors

Abstract

The immobilization of acetylcholinesterase on different nanomaterials has been widely used in the field of amperometric organophosphorus pesticide (OP) biosensors. However, the molecular adsorption mechanism of acetylcholinesterase on a nanomaterial's surface is still unclear. In this work, multiscale simulations were utilized to study the adsorption behavior of acetylcholinesterase from Torpedo californica (TcAChE) on amino-functionalized carbon nanotube (CNT) (NH₂–CNT), carboxyl-functionalized CNT (COOH–CNT) and pristine CNT surfaces. The simulation results show that the active center and enzyme substrate tunnel of TcAChE are both close to and oriented toward the surface when adsorbed on the positively charged NH₂–CNT, which is beneficial to the direct electron transfer (DET) and accessibility of the substrate molecule. Meanwhile, the NH₂–CNT can also reduce the tunnel cost of the enzyme substrate of TcAChE, thereby further accelerating the transfer rate of the substrate from the surface or solution to the active center. However, for the cases of TcAChE adsorbed on COOH–CNT and pristine CNT, the active center and substrate tunnel are far away from the surface and face toward the solution, which is disadvantageous for the DET and transportation of enzyme substrate. These results indicate that NH₂–CNT is more suitable for the immobilization of TcAChE. This work provides a better molecular understanding of the adsorption mechanism of TcAChE on functionalized CNT, and also provides theoretical guidance for the ordered immobilization of TcAChE and the design, development and improvement of TcAChE-OPs biosensors based on functionalized carbon nanomaterials.