A pair of small redox peaks appear in the cyclic voltamogram (CV) of the HRP/MWCNTs/CFUME (b) and MWCNTs/CFUME (c), and the anodic and cathodic peak potentials are located at about 0 V and - 0.1 V, respectively. This is attributed to the reduction and oxidation of carboxylic acid groups at the surface of MWCNTs. These groups were reduced to -CH2OH coupled with four electrons. Moreover, the background current was very large compared with that of bare CFUME (curve e) because of the increased surface charge [16]. A pair of stable and well-defined redox peaks with regard to Fe(III) to Fe(II) conversion of the immobilized HRP were observed on HRP-AuNCs/MWCNTs/CFUME (a). The anodic and cathodic peak potentials were - 0.10 V and - 0.21 V (vs. Ag/AgCl) at 100 mV/s, respectively. The formal potential (Eo’), obtained by averaging the potential values of the anodic and cathodic peaks (Epa and Epc), was - 0.16 V with a peak potential separation of approximately 110 mV, indicating a quasi-reversible process [17] The peak current did not change after 100 cyclic scans. This indicated that the HRP-AuNCs/MWCNTs film on the electrode surface was very stable. HRP/MWCNTs/CFUME (b) did not show a characteristic peak of HRP, which indicates that the AuNCs acting as the molecular electric wire can help to transfer the electron between the active center of the enzyme and the electrode. HRP-AuNCs/CFUME (d) did not show obvious redox peaks, and the current was much lower. This may be because the HRP-AuNCs could barely be absorbed on the bare CFUME without the aid of the MWCNTs. The enlarged interface area and good conductivity of the MWCNTs, which provides many efficient paths for direct electron conduction between the HRP-AuNCs and the CFUME, enhanced the current signals [18].