Researchers at the University of Tennessee and Oak Ridge National Laboratory are using molecular dynamics simulations (MD) to show that large electro-osmotic flow can be turned into a large net ionic current via ion-selective filtering by a DNA molecule inside the carbon nanotube. The group shows that the "ion filtering" action of just one segment "sitting" at the tube exit may cause a significant enhancement in ion current.

The measured increase in current, which is occasionally followed by strong ionic current spikes (shown in the figure above) could be a consequence of the consecutive accumulation of these "filtering" effects. Namely, the timescale of a typical MD simulation is of the order of ns, while the increase in ionic current is measured over a timescale that is many orders of magnitude longer (seconds) through the buildup of 20 nm long DNA segments at the exit of a 2 µm SWCNT.

The electrostatic barriers at the tube ends and cation-mediated electro-osmotic current, caused by the electrical double layer around the negatively charged DNA and on the charged SWCNT surface, help to keep DNA in the nanotube. This stimulates the accumulation of the DNA segments at the exit.

More details can be found in the journal Nanotechnology.