Jul 8, 2011
Passivated nanopores withstand extreme voltages
Solid-state nanopores are a core element of next-generation single molecule tools in the field of nanobiotechnology, most prominently in the area of DNA-sequencing technology. Researchers at the IBM T. J. Watson Research Center have recently introduced a nanopore-based DNA sequencing platform, which they call a DNA transistor. Thin-film electrodes are integrated into the nanopore device for electrically interacting with translocating DNA. They have now shown that TiN electrodes inside a nanopore can be passivated and completely shielded against electrochemical deterioration even when extreme voltages are applied.
The quest to quickly and affordably sequence DNA and other nucleic acids is driven by the information contained in these molecules that lies at the core of genomics, cell and molecular biology, and healthcare, to name just a few. IBM researchers have recently proposed a next-generation sequencing technology that is based on threading a DNA molecule through a tiny nanopore in a freestanding, solid-state membrane integrated with several nanoelectrodes.Their device, which they call a DNA transistor, is designed to control the motion of a DNA molecule as it translocates through the nanopore by carefully biasing the metal electrodes in order to create particular electric fields inside the nanopore that interact with charges on the DNA molecule. Precise control of these fields would enable trapping a DNA molecule within the nanopore, moving it base-by-base on demand, and reading its sequence along the way.
In addition to the IBM team, many groups of scientists around the world are looking into using metal electrodes in nanopore technologies. However, applying voltages to metals in solution can lead to a wealth of electrochemical reactions that hinder the devices or even destroy them. Typically this would lead to corrosion of the electrodes to the point where they no longer function or they grow in the pore and eventually close it off. Also, at modest applied voltages, the water in solution can be decomposed into hydrogen and oxygen bubbles at the electrodes, which can easily block DNA from moving through the pore.
The scientists at IBM have developed a plasma-based passivation scheme for nanopore electrodes that fully shields them from electrochemical deterioration and the formation of bubbles within the pore. Even when applying voltages as high as +4.5 V for up to 24 hours, the passivated TiN electrodes remained intact and did not modify the nanopore. Unpassivated electrodes corroded in just minutes at these potentials and in an hour the pores were more than halfway closed off by the corrosion. The group also added glycerol to the solution to mitigate water decomposition inside the nanopore and avoid bubble formation.
The reported work is a significant step to control electrochemical effects in the DNA transistor device, but could be useful for a broad range of applications such as biosensors and lab-on-a-chip devices.
The researchers presented their work in the journal Nanotechnology.
About the author
Stefan Harrer, PhD, and Philip S Waggoner, PhD, are research scientists in the DNA Transistor Team headed by Gustavo A Stolovitzky, PhD, at the IBM T. J. Watson Research Center in Yorktown Heights, New York, US. The other authors in the paper are Binquan Luan, Ali Afzali-Ardakani, Dario L Goldfarb, Hongbo Peng, Glenn Martyna and Stephen M Rossnagel. The group is currently developing a next-generation nanopore-based DNA-sequencing device called the DNA-transistor.