Graphene may hold key to speeding up DNA sequencing

Extremely thin membrane, a mere one-atom thick, lives up to its acclaim as a 'rapidly rising star'

Cambridge, Mass. - September 9, 2010 - In a paper published as the cover story of the September 9, 2010 Nature,
researchers from Harvard University and MIT have demonstrated that
graphene, a surprisingly robust planar sheet of carbon just one-atom
thick, can act as an artificial membrane separating two liquid
reservoirs.
By drilling a tiny pore just a few-nanometers in diameter, called a
nanopore, in the graphene membrane, they were able to measure exchange
of ions through the pore and demonstrated that a long DNA molecule can
be pulled through the graphene nanopore just as a thread is pulled
through the eye of a needle.

"By measuring the flow of ions passing through a nanopore drilled in
graphene we have demonstrated that the thickness of graphene immersed in
liquid is less then 1 nm thick, or many times thinner than the very
thin membrane which separates a single animal or human cell from its
surrounding environment," says lead author Slaven Garaj, a Research
Associate in the Department of Physics at Harvard. "This makes graphene
the thinnest membrane able to separate two liquid compartments from each
other. The thickness of the membrane was determined by its interaction
with water molecules and ions."
Graphene, the strongest material known, has other advantages. Most importantly, it is electrically conductive.

"Although the membrane prevents ions and water from flowing through
it, the graphene membrane can attract different ions and other chemicals
to its two atomically close surfaces. This affects graphene's
electrical conductivity and could be used for chemical sensing," says
co-author Jene Golovchenko, Rumford Professor of Physics and Gordon
McKay Professor of Applied Physics at Harvard, whose pioneering work
started the field of artificial nanopores in solid-state membranes.
"I believe the atomic thickness of the graphene makes it a novel
electrical device that will offer new insights into the physics of
surface processes and lead to a wide range of practical application,
including chemical sensing and detection of single molecules."

In recent years graphene has astonished the scientific community with
its many unique properties and potential applications, ranging from
electronics and solar energy research to medical applications.
Jing Kong, also a co-author on the paper, and her colleagues at MIT
first developed a method for the large-scale growth of graphene films
that was used in the work.
The graphene was stretched over a silicon-based frame, and inserted
between two separate liquid reservoirs. An electrical voltage applied
between the reservoirs pushed the ions towards graphene membrane. When a
nanopore was drilled through the membrane, this voltage channeled the
flow of ions through the pore and registered as an electrical current
signal.

When the researchers added long DNA chains in the liquid, they were
electrically pulled one by one through the graphene nanopore. As the DNA
molecule threads the nanopore, it blocks the flow of ions, resulting in
a characteristic electrical signal that reflects the size and
conformation of the DNA molecule.
Co-author Daniel Branton, Higgins Professor of Biology, Emeritus at
Harvard, is one of the researches who, more than a decade ago, initiated
the use of nanopores in artificial membranes to detect and characterize
single molecules of DNA.
Together with his colleague David Deamer at the University of
California, Branton suggested that nanopores might be used to quickly
read the genetic code, much as one reads the data from a ticker-tape
machine.

As a DNA chain passes through the nanopore, the nucleobases, which
are the letters of the genetic code, can be identified. But a nanopore
in graphene is the first nanopore short enough to distinguish between
two closely neighboring nucleobases.
Several challenges still remain to be overcome before a nanopore can
do such reading, including controlling the speed with which DNA threads
through the nanopore.
When achieved, nanopore sequencing could lead to very inexpensive
and rapid DNA sequencing and has potential to advance personalized
health care.

"We were the first to demonstrate DNA translocation through a truly
atomically thin membrane. The unique thickness of the graphene might
bring the dream of truly inexpensive sequencing closer to reality. The
research to come will be very exciting," concludes Branton.

http://www.eurekalert.org/pub_releases/2010-09/hu-gmh091010.php