Recently, great interests were taken to the nanostructures such as nanorods, nanowires, nanotubes and nanoparticles modified electrodes as chemical or bio sensors. Those modified electrodes showed a significant increase in both selectivity and sensitivity in different biosensors such as glucose, immoassay, DNA. In this postal, vertically aligned nanowire array electrodes (NAEs) were prepared by electrodeposition of gold into an anodic aluminium oxide membrane (AAM), providing an ordered three dimensional (3D) matrix for immobilization of redox proteins.
Third-generation H2O2 biosensors were prepared by covalent immobilization of horseradish peroxidase (HRP) on the self-assembled monolayer modified NAEs. Direct electron transfer and electrocatalytic performances of the HRP/NAEs with different nanowire lengths (deposition time of 2, 4 and 5 h) were investigated. Results showed that with longer nanowires, better performances were achieved. The HRP/NAE5h (5 h deposition time) exhibited remarkable sensitivity (57.95 μA mM-1 cm-1) towards H2O2 with a detection limit of 0.42 μM (S/N = 3), linearity up to 15 mM and a response time of 4 sec. The ordered 3D gold nanowire array with high conductivity, excellent electron transfer capability and good biocompatibility proved promising for fabricating sensitive, selective, stable and mediator-free enzymatic biosensors.
Fig. (A) shows the SEM images of the gold nanowire modified electrodes. The average lengths of the nanowires are 20µm. Fig. (B) shows the cyclic voltammograms of the HRP/NAE2h in 50 mM PB, pH 7.0 in the absence and presence of 100 μM H2O2. The typical current-time responses of different HRP/NAEs and the HRP/Au electrode at -0.1 V with successive addition of 10 μM of H2O2 were illustrated in Fig. (C). The signal response of H2O2 at the HRP/NAEs was large compared to that of the flat electrode, reflecting superior performances of the gold nanowire electrodes.
To the best of our knowledge, this is the first third-generation H2O2 biosensor based on the direct electrochemistry of HRP immobilized on a SAM-modified gold nanowire array electrode. The resulting HRP/NAEs displayed prominent improvement regarding electroactivity, sensitivity and stability, comparing with the HRP/flat gold electrodes.