"There is a high demand to track mutations for cancer research or future applications in personalized medicine," said Peiming Zhang of Arizona State. "Currently the main issue in doing this type of detection is that it is still costly and time consuming."
The new technique is very sensitive as, depending on the exact permutations, an SNP can change the electrical conductance of a double-stranded DNA molecule by as much as an order of magnitude. Different mutations cause either an increase or decrease in conductance.
"We have developed a technology that allows us to wire single molecules into an electrical circuit," said Nongjian Tao of Arizona State. "We can now directly read the biological information in a single DNA molecule."
The team tested DNA that was 11 or 12 bases long. The researchers applied a monolayer of thiolated double-stranded DNA molecules to a gold substrate. Then they touched the molecules with a gold scanning tunnelling microscope (STM) tip before drawing the tip away while monitoring the current. Steps in the current decay indicated the presence of DNA molecules attached to the tip. Repeating this process thousands of times enabled the team to build up data about the electrical conductivity of single molecules.
"There are two things required to make a reliable measurement," said Tao. "One is that the DNA has to be tethered between two electrodes and the other is that it should be done in a slightly salty, water environment to minimize any perturbations to the structure of the molecule."
The mechanism for current flow through DNA is as yet unclear. The researchers believe that electrons may tunnel through the molecule or that charge-hopping may be taking place.
Now the researchers plan to automate the measurement steps, enabling analysis of many DNA sequences simultaneously.
The researchers reported their work in PNAS.