Nanofiber-guided orientation of electrospun carbon nanotubes and fabrication of aligned CNT electrodes for biodevice applications

Abstract

Carbon nanotubes (CNTs) have quite large specific surface areas and high electron transfer rates. They are thus anticipated to be valuable for the construction of high-power biodevices, such as biosensors and biofuel cells. However, CNTs tend to aggregate due to van der Waals forces, which generates electrical resistance. Optimal use of their properties cannot be achieved simply by incorporating CNTs into electrodes. A technique for orienting CNTs on electrode surfaces is thus urgently needed. In this study, we aimed to develop a CNT alignment method to maximize the intrinsic conductive and structural properties of CNTs. We used poly(ethylene-co-vinyl acetate) (PEVA) nanofibers to guide CNT orientation during electrospinning. A mixed solution of PEVA and CNT was spun onto the surfaces of Au substrates. Following electrospinning, combustion at 400 °C pyrolyzed the PEVA nanofibers, leaving only CNTs on the substrates. After combustion, the morphology and chemical state of the CNTs were evaluated with scanning electron microscopy (SEM), field-emission SEM, and Raman spectroscopy. We then immobilized enzyme onto modified the CNTs and evaluated their electrochemical performance. Examination of the spun CNT-PEVA core-sheath nanofibers following combustion confirmed that the CNTs were oriented in the direction of the fibers. Impedance measurements of the enzyme-immobilized electrodes showed that the charge transfer resistance was lower with the aligned CNTs than with randomly oriented CNTs. The enzymatic electrochemical reaction was evaluated in cyclic voltammetry tests. We found that the CNT alignment on the electrode surface increased the current in enzyme-substrate redox reaction.