Science 327, 64–67 (2010)

Nanoscale pores can be used as DNA sequencers and single-molecule counters, and can be made from carbon nanotubes. Gas, water, ions and DNA have all been made to pass through carbon nanotube pores. Now Colin Nuckolls and colleagues at Columbia University, Arizona State University and Oak Ridge National Laboratory have discovered that carbon nanotube pores can pass anomalously high ionic currents.

The researchers measured the ionic current driven by an applied voltage between two fluid reservoirs connected by an individual single-walled carbon nanotube. They found that ionic conductivities ranged over four orders of magnitude for different tubes, with the highest values exceeding expected values by an order of magnitude or more. The high-conductivity tubes were also able to transport single-stranded DNA between the reservoirs. Because DNA is negatively charged, the transport event was accompanied by ionic conduction. Surprisingly, the magnitude of this conduction was orders of magnitude greater than expected given the quantity of DNA transported.

The high ionic conductivities could be due to net-charge imbalances inside the nanotubes, leading to electroosmotic current and large changes in the polarization of the buffer outside the tubes. Nuckolls and colleagues also suggest that the results could be exploited to fabricate a DNA sequencer in which a metallic nanotube serves both as a pore and an integrated electrode.