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IMPROVING DNA SEQUENCING WITH GRAPHENE
One-atom thick layers of graphene can make human DNA sequencing faster and cheaper. The study of researchers at the Harvard University and MIT - Massachusetts Institute of Technology, published in Nature

One-atom thick layers of graphene can help make human DNA sequencing faster and cheaper. This is the result of a study carried out by a research team at the Harvard University and the MIT -Massachusetts Institute of Technology – published in the review Nature.

As mentioned in the MIT Technology Review, it takes several days to implement the techniques that are currently in use for this purpose, which cost thousands and thousands of dollars. On the other hand, the new graphene-based sequencing method uses the nanopore technique, which allows to analyze a whole genome in a matter of few hours.

More specifically, this is how DNA sequencing with the nanopore technique works: a DNA filament is driven through a hole in a membrane, usually suspended in saline solution, to which stress is applied. The ions move from one side of the membrane to the other, producing electric power: as each of the 4 nitrogenous bases passes through the pore, power intensity changes to a different extent, and such changes – if appropriately recorded – could allow to punctually recognize the nucleotides.

However, the process has a limit that would be overcome with the use of graphene. The nanopores studied so far are engraved on 20 to 30 nm thick membranes. The distance between 2 bases is 0.5nm, therefore 40-60 bases pass each time through the opening during the process, preventing accurate identification. The graphene membrane – only 1nm thick – is “the thinnest ever applied to address this issue,” says Jene Golovchenko, professor of physics at Harvard and head of the study.

In order to test the innovative material, the researchers created their own membrane by placing a layer of graphene over a 200nm wide opening in a silicon nitride surface. Then they made a few nanometres wide hole in graphene using an electronic beam. When the membrane was finally placed in saline solution in contact with silver electrodes, the scientists observed power variations upon the passing of the filament through the pore, thus demonstrating that this method could be effective to identify DNA.

This is an important step that, however, still requires lot of studies, say the experts. As stressed by John Kasianowicz, biophysicist at the National Institute of Standards and Technology and the inventor of nanopore-based sequencing, the study describes how each DNA molecule, which contains thousands of bases, passes through the pore very quickly, in hundreds of microseconds (approximately 4 nanoseconds per base). On the other hand, in order to read each individual base, the filament should remain inside the pore 1000 times longer.

Thus, sequencing a DNA filament requires the ability to control and slow down its passage through the membrane – a barrier that is still to be overcome.

Source: MIT Technology Review
The Editorial Staff
Published on Monday, January 21, 2013

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