Abstract:

The quartz-crystal microbalance technique was used to monitor the adsorption of glucose oxidase (GOx) on bare Au, Au-electrodeposited Au (Au_ed/Au), multiwalled carbon nanotube (MWCNT)- modified Au (MWCNTs/Au), and Au-electrodeposited MWCNT-modified Au (Au_ed/MWCNTs/Au) electrodes. The mass of GOx at saturated adsorption was obtained in each case. The amperometric responses of these enzyme electrodes were examined, and the mass-specific bioactivities of the immobilized (adsorbed) GOx (MSBA_i) were evaluated through anodic potentiostatic detection of enzymatically generated H₂O₂ in the presence of glucose. The direct electrochemistry of adsorbed GOx was studied by cyclic voltammetry, to obtain the electroactivity percentage of the immobilized (adsorbed) GOx (EAP_i) in each case. We found that the amounts of enzyme adsorbed and the amperometric responses of these enzyme electrodes follow the order MWCNTs/Au > Au_ed/MWCNTs/Au > Au_ed/Au > Au; MSBA_i follows the order of Au > Au_ed/MWCNTs/Au > Au_ed/Au > MWCNTs/Au; and EAP_i follows the order of MWCNTs/Au > Au_ed/MWCNTs/Au > Au_ed/Au > Au. The experimental data are interpreted based on hydrophobic/hydrophilic interactions among enzyme molecules and the nanomaterials, as well as the amount of adsorbed GOx. It was also verified that the total enzymatic activity of all the electrode-adsorbed enzyme molecules is positively related to the amperometric responses of the enzyme electrodes. This work is useful in studying the immobilization of enzyme on nanomaterials and thus-prepared amperometric enzyme electrodes.

Key words: Quartz crystal microbalance, Glucose oxidase, Mass-specific bioactivity, Electroactivity percentage, Multiwalled carbon nanotubes, Electrodeposition of Au nanoparticles