Nanoelectrodes could provide bird 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 – each end of a DNA strand was attached to an electrode, leaving it suspended above the trench, like a tightrope across a valley.

To test the approach, the team used a DNA strand that exactly matched a gene sequence from the H5N1 avian flu virus.

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.

Virus probe

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.

Journal reference: Nano Letters (DOI: 10.1021/nl0716451

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