by Andre on 16 March 2008
The team began with a nanotube—a tiny tube of carbon about as thick as DNA itself—that was integrated within a simple electrical circuit. A 6-nm section of the nanotube was removed using plasma ion etching. This procedure not only cuts the tube, but also oxidizes the remaining tips. This makes it possible to bridge the gap with a DNA molecule with ends that have been designed to form strong chemical bonds with the oxidized tips.
This meant that they had a reliable, well defined connection between the bridging DNA molecules and the nanotube electrodes that allowed them to do their measurements in water at room temperature. Since everything is bathed in water they could add a DNA cutting enzyme to show that this breaks the circuit they formed and could also de-hybridze their bridging double strands, leaving only a single strand with a known sequence. Then, by flowing in an almost complementary strand, they could measure the effect of single base mismatches. Even a single mismatch increased the DNA’s resistance by 300 fold.
This structural sensitivity poses a significant challenge to anyone dreaming of making self-assembled circuits directly from DNA, but their system might also make a nice miniaturizable device for detecting single nucleotide polymorphisms, or SNPS. For this to be feasible, one of the first things they would need to improve is the rate at which they get successful DNA bridging. Right now it’s a bit low for commercial applications with their method producing “10 working devices out of 370 that were tested.”
For more, check out my news story at physicsworld.com.