Two months ago we reported that University of Pennsylvania researchers were able to create a tiny nanopore within graphene, sheet of carbon one atom thick, and detect DNA molecules passing through the opening. Now a collaboration of scientists from Harvard and MIT is reporting in a cover story in Nature that they were able to measure the ionic flow through a nanopore of their own making. They studied the properties of graphene when it’s separating two ionically variable liquids and showed graphene sheets function as “ionic insulators with a very small stable conductance that depends on the ion species in solution.”
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.
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.
More from Harvard: Graphene may hold key to speeding up DNA sequencing…
Abstract in Nature: Graphene as a subnanometre trans-electrode membrane
Flashback: Graphene Carbon Nanosheets as Platform for Electronic DNA Sequencing