An electron tunneling-based technology for accurately reading the base sequence of DNA molecules has been developed by an Arizona State University (ASU) research team headed by Dr. Stuart Lindsay. This is the first tunneling-based DNA reader that can discriminate among DNA's four bases in one tunnel gap. If the technology can be perfected, DNA sequencing could be performed much more quickly than by current technologies, and at a fraction of the cost. The ASU work was supported, in part, by funding from the National Human Genome Research Institute’s “$1000 Genome” initiative, which is intended to make DNA genome sequencing as widespread as a routine medical checkup, thus helping to usher in the era of “personalized medicine.” The new technology relies on a scanning tunneling microscope and an atomic force microscope, to make its measurements. The microscopes have a delicate electrode tip that is held very close to the DNA sample. In its current innovation over earlier versions, Dr. Lindsay's team made two gold electrodes, one on the end of the microscope probe, and another on the surface, that had their tiny ends chemically modified to attract and catch the DNA between a gap, like a pair of chemical tweezers. The gap between these functionalized electrodes had to be adjusted to find the hydrogen-bonding sweet spot, so that when a single chemical base of DNA passed through a tiny, 2.5-nanometer opening between the two electrodes, it momentarily sticks to the electrodes and a small increase in the current is detected. Any smaller, and the molecules would be able to bind in many configurations, confusing the readout; any larger and smaller bases would not be detected. "What we did was to narrow the number of types of bound configurations to just one per DNA base," said Dr. Lindsay.
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