Single-walled carbon nanotubes were chemically functionalized by virtue of the interactions between the nanotube-bound carboxylic moieties and octadecylamine ligands. The electronic conductivity properties of the resulting nanotubes were probed voltammetrically. Two approaches were employed. The first entailed the fabrication of a nanotube monolayer at the airwater interface and the conductivity was measured in situ with a vertically aligned interdigitated arrays (IDAs) electrode. The overall current profiles are analogous to those of a Coulomb blockade and the conducting current pathways are found to be one-dimensional within the two-dimensional arrays of nanotubes. The second technique was taking advantage of the dispersibility of the nanotubes in a solution where conventional electrochemical methods were used. From these measurements, the nanotube bandgap energy could also be estimated, which was quite comparable to that determined by spectroscopic measurements. 2005 Elsevier Ltd. All rights reserved.