| ||Model of Graphene Structure/Creative Commons|
Since its discovery in 2004, graphene has captured imaginations and sparked innovation in the scientific community. Perhaps rightly so as it is 200 times stronger than the strongest steel but still flexible, incredibly light but extremely tough, and conducts heat and electricity more efficiently than copper.
Professor Jerry Bernholc of North Carolina State University is utilizing the National Center for Supercomputing Applications’ Blue Waters supercomputer at the University of Illinois at Urbana-Champaign to explore graphene’s applications, including its use in nanoscale electronics and electrical DNA sequencing.
Graphene and nanoscale electronics
Currently, the trend toward smaller silicon semiconductors seems to be slowing down as it reaches limits of small scale. The world is moving past Moore’s Law, the idea that every two years computer processing speed will double and costs will decrease. Transitior density is still increasing but speed increases have slowed dramatically. In addition to that, systems are no longer shrinking like they did in the past as transistors reach physical limits.
This is bad news for those trying to use very fast computers, or any electronics for that matter, that have been getting thinner and thinner.
However, graphene may be a new way forward.
“We’re looking at what’s beyond Moore’s law, whether one can devise very small transistors based on only one atomic layer, using new methods of making materials,” Bernholc says. “We are looking at potential transistor structures consisting of a single layer of graphene, etched into lines of nanoribbons, where the carbon atoms are arranged like a chicken wire pattern. We are looking at which structures will function well, at a few atoms of width.”
Trying to do computations like this on normal computers is impossible, so Bernholc and his team utilized the Blue Waters supercomputer.
“We are doing quantum mechanical computations with thousands of atoms, and several thousands of electrons, and that requires very fast, very powerful systems, and we need to do calculations in parallel,” Bernholc says. “The computer chips are not fast enough — one computer chip in a desktop machine cannot do such calculations. On Blue Waters, we use thousands of nodes in parallel, so we can complete quantum mechanical calculations in a time that’s practical and receive results in a timely fashion.”
Blue Waters Supercomputer
Graphene and DNA sequencing
Bernholc is among the researchers who think that graphene may also play a major role in the push to decrease prices for gene sequencing. With 19 companies offering personal, direct-to-consumer genetics tests, it is easier than ever to sequence DNA, learning your family history and identifying genetic risks.
Some forms of sequencing DNA include electrophoresis, which involves running a current through gel with DNA segments in it, causing DNA strands of varying lengths to move to different locations (shorter strands move faster). This allows comparison between known DNA strands and unknown ones.
As graphene is an excellent conductor of electricity, it is not surprising its use in gene sequencing is being explored. Recently, a group of researchers in California explored the possibility of using nanotubes (a tubular cousin of graphene) to electrically detect a single nucleotide addition during DNA replication. If the nucleotides can also be distinguished electrically, one would be able to sequence DNA and other genetic materials more cheaply and accurately. Currently, DNA sequencing involves complex labeling and readout schemes, which are quite costly and time-consuming. But nanotubes could lead to a simple nanocircuit that could operate faster and be much cheaper.
Bernholc and his team ran calculations to reproduce the California experiment, but changed the electrical conditions. This enabled them to perform calculations that allowed for some DNA base pairs to be distinguished, but not others. There are four chemical bases that are used to store information in DNA: adenine (A), guanine (G), cytosine (C) and thymine (T). The sequence of the DNA tells the cells in your body what proteins and chemicals to make. The bases pair up with each other (A with T and C with G) to form base pairs.
“That allows us to distinguish A from T. G and T are very clear, we can tell G and T from C and A, but we cannot distinguish C and A at the moment using graphene,” Bernholc says. “That’s where more work is needed, but we are moving towards being able to have a new way to sequence DNA.”
For Bernholc’s team and other researchers, the possibilities for graphene’s applications — nanoscale electronics, DNA sequencing and beyond — seem endless.