Joined: 16 Mar 2004
|Posted: Tue Aug 19, 2008 12:04 pm Post subject: Nanotube electrodes could provide avian flu test
|Nanotube electrodes could provide avian flu test
Detecting the presence of specific genes in a DNA sample can be like looking for a needle in a haystack. Now scientists have demonstrated a new process that could make the task far easier – it's all done by wiring a DNA strand up to a pair of nanotube electrodes and feeding electricity through it.
Researchers from Florida International University, US; Pohang University of Science and Technology, Korea; and the National Institute of Genetics, Japan, took a single-walled carbon nanotube and deposited titanium and gold at either end to create a pair of electrical contacts.
Then they used an ion-beam to remove a central section of the tiny tube, cutting it in half to create two electrodes separated by a gap roughly 27 nanometres wide. At the same time, the ion-beam also etched a shallow trench between the electrodes in a silicon substrate.
The 27 nm gap was not a random choice. That is the length of a segment of 80 base pairs of DNA from the H5N1 gene of the avian flu virus, and meant that each end of the strand could be attached to an electrode, leaving it suspended above the trench, like a tightrope across a valley. Then the scientists then switched on the juice…
They saw a current in the range of 25-40 picoamps flow between the carbon nanotubes electrodes when a double strand of DNA bridged the gap. By comparison, a single-strand, with one half of its base pairs missing, carried less than 1 pA.
Furthermore, previous research has shown that a double strand of DNA with non-matching base pairs lets considerably less current flow through it than a pair of matching strands.
So the team believes that a probe of a similar design could be used to identify specific genes.
If a single strand or a double strand with unmatching base pairs bridges the electrodes, the current should be low. But when a strand that matches the sample being investigated falls into the gap, the current should rise significantly. This change should be a dead giveaway that the sample contains the specific gene being sought.
"The study demonstrates that single-walled nanotubes can be employed as efficient nanoelectrodes for direct measurements of charge transport in DNA," the researchers write in a paper that will appear in the journal Nano Letters.