Oct 23, 2012
DNA translocating through a carbon nanotube can increase ionic current
Partial blockade of ionic current by DNA molecules has been observed by many researchers who are developing third-generation DNA sequencing based on single molecule, electric field driven transport through biological or synthetic nanopores, filled with an electrolyte. However, translocation of short segments of a single-stranded DNA through a narrow, long, single-walled carbon nanotube can be accompanied by large increases of ion current, as observed recently by a research team at Arizona State University.
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.
About the author
The study was conducted by research teams of the Joint Institute of Computational Sciences (JICS) of the University of Tennessee and Oak Ridge National Laboratory in Oak Ridge and the Biodesign Institute of Arizona State University (ASU) in Tempe, US, as a part of collaborative research funded by the National Human Genome Research Institute of the US National Institutes of Health. Dr Jae Hyun Park was an ORISE postdoctoral fellow and is now assistant professor at Gyeongsang National University, South Korea. He performed the MD calculations guided by Dr Predrag Krstic, a JICS senior scientist, adjunct professor in physics at University of Tennessee and founder of the TheoretiK consulting company. Dr Stuart Lindsay is professor of Physics and Chemistry at ASU and Director of the Center for Single Molecule Biophysics at the Biodesign Institute. Dr Jin He was a research assistant professor at ASU, and is currently assistant professor at Florida International University in Miami. Dr Brett Gyarfas is a research engineer at the Biodesign Institute of ASU.