Enzymatic Biosensor for Hydrogen Peroxide Based on the Direct Electron Transfer on MWCNTs/IL/CPO-GC: The Dual Function of Ionic Liquids

Abstract

Chloroperoxidase (CPO) is a versatile peroxidase which can exhibit peroxidase, catalase and cytochrome P450-like activities in addition to chlorination of activated C-H bonds. However, the direct electron transfer (DET) is difficult to be achieved of CPO due to its heme prosthetic group buried deeply inside. In this work, ionic liquid (brominated 1-ethyl-3-methylimidazole, IL) and MWCNTs (multiwall carbon nanotubes) were employed to modify the glassy carbon electrodes (GC) to develop a simple biosensor MWCNTs/IL/CPO-GC for H2O2 without the need to use redox mediator. MWCNTs/IL/CPO-GC has good stability, longer service life and repeatability. The The detection limit was as low as 0.15μmol L−1. The function of IL on DET was elucidated using UV-vis, CD, fluorescence spectroscopy, and the thermodynamic parameters. It was found that besides the enhanced activity of CPO and improved solubility of MWCNTs, the open of the substrate channel to the active site at heme prosthetic group in CPO was widen in the presence of IL so as that the heme became more exposed for easier access. Meanwhile the α-helix secondary structure of CPO was strengthened. The biosensor was applied to the determination of H2O2 in contact lens care solutions and pure milk with a good accuracy and recovery.