Single-Walled Carbon Nanotube Network Ultramicroelectrodes

Ultramicroelectrodes (UMEs) fabricated from networks of chemical vapor deposited single-walled carbon nanotubes (SWNTs) on insulating silicon oxide surfaces are shown to offer superior qualities over solid UMEs of the same size and dimensions. Disk shaped UMEs, comprising two-dimensional "metallic" networks of SWNTs, have been fabricated lithographically, with a surface coverage of <1% of the underlying insulating surface. The electrodes are long lasting and give highly reproducible responses (either for repeat runs with the same electrode or when comparing several electrodes with the same size). For redox concentrations <or=1 mM the steady-state behavior of SWNT network UMEs is as expected for conventional solid metal UMEs (e.g., Pt, Au), due to diffusional overlap between neighboring SWNTs. Importantly, the low intrinsic capacitance of the SWNTs and much reduced surface area lead to much faster response times and lower background currents. The well-defined geometry of the SWNT network electrode is also useful for studying electron transfer (ET) kinetics at SWNTs. Given the intrinsically high mass transport rates to SWNTs within a network electrode, the reversible nature of the CVs recorded for Ru(NH 3) 6 (3+/) (2+) and FcTMA (+/) (2+) suggests that ET driven solely by defects on the sidewalls of the SWNTs is highly unlikely.