Harvard-MIT Study Examines Graphene

Graphene—a one-atom-thick carbon complex—could be the key to a faster and cheaper method for sequencing DNA, according to a study published by Harvard and MIT researchers that was featured as the cover story in a recent issue of the journal Nature.

The researchers used an electron beam to puncture tiny holes known as nanopores into a graphene membrane. When submerged in an ionic solution, the membrane separates two liquid reservoirs, allowing charged molecules like DNA to traverse through the pores. As the DNA channels through, each base produces a distinct electrical signal.

The researchers were able to detect these signals—a discovery they said gives scientists the ability to decode an entire strand of DNA.

According to the researchers, their findings offer advantages to existing techniques.

Current methods require undertaking multiple reactions that can take hours to complete. The researchers said that their new nanopore technology—which completes sequencing in a single step—can potentially speed up this process, facilitating rapid sequencing of entire genomes.

“One of the long-term goals is to use nanopores for sequencing DNA, and to do that one [must] be able to distinguish one base from the next,” said the study’s senior author, Daniel Branton, who is also an emeritus professor of biology at Harvard and a principal investigator at the Harvard Nanopore Group.

Pore length is crucial when identifying individual DNA bases, Branton said, adding that the study “represents the first time that a molecule—DNA in our case—has been put through a nanopore that is extremely short.”

Scientists in the past have studied protein-based nanopores that span five to 10 nanometers in length. But because the distance between two bases in a DNA molecule is 0.5 nanometers, such pores are ineffective, as they obstruct the resolution of 10 to 15 bases at a time.

In contrast, graphene nanopores—which span a length of 0.5 nanometers—allow a single base to occupy the pore at a time, which resolves this problem.

Branton said that the challenge at this stage is to control the motion of the DNA. Since molecules must move slowly for scientists to detect differences in signal output, the DNA must move even more slowly in order to improve sequencing accuracy, Branton added.

“Our emphasis right now is [on executing] controlled motion of the [DNA] molecule,” Branton said. “There are a lot of interesting features [that] need to be explored so we can enhance or hopefully learn more about how graphene can be used as a sensor.”