High sensitivity carbon nanotube tower electrodes

Highly aligned multi-wall carbon nanotubes (MWCNT) were synthesized in the shape of towers and used to fabricate chemical sensor electrodes. The towers were fabricated on an Fe/Al₂O₃/SiO₂/Si substrate with the Fe catalyst patterned in 1 mm × 1 mm blocks with 100 μm spacing between the blocks. Thermally driven chemical vapor deposition was used for the nanotube synthesis process. Patterned MWCNT towers up to 4 mm high were grown and easily peeled off the silicon substrate. The synthesized MWCNT towers were characterized by environmental scanning electron microscopy and high resolution transmission electron microscopy. A sensor electrode was then formed by casting epoxy into the tower under pressure and polishing both ends of the tower. One end of the tower served as an electrical connection and the other as a nanoscale array electrode. Cyclic voltammetry (CV) for the reduction of 6.0 mM K₃Fe(CN)₆ and Ru(NH₃)₆Cl₃ (in a 1.0 M KNO₃ supporting electrolyte) was used to examine the surface properties of the nanotube tower electrode. The CV results showed a steady-state response up to 2 V/s attributable to radial diffusion with a high steady-state current density. Cyclic voltammetry testing of these two redox systems showed a sigmoidal shape indicating radial diffusion and high sensitivity at the electrode. Based on the CV results, the carbon nanotube array electrode is a promising candidate for future highly sensitive chemical and biosensor applications.