David Kirkpatrick

August 19, 2010

Graphene and DNA sequencing

News on potential applications of graphene is always interesting, but I’ll have to admit I’d like see more actual market-ready solutions. This news is both intriguing and promising, but the nut graf contains those dreaded words, “could help (insert the gist of any story here).” It’ll be a pretty exciting day when I blog about something that will help, instead of could help with graphene as the key helping element.

From the second link:

Layers of graphene that are only as thick as an atom could help make human DNA sequencing faster and cheaper. Harvard University and MIT researchers have shown that sheets of graphene could be a big improvement over membranes that are currently used for nanopore sequencing–a technique that promises to speed up and simplify the sequencing of long strands of DNA.

And:

The researchers create their membrane by placing a graphene flake over a 200-nanometer-wide opening in the middle of a silicon-nitride surface. Then they drill a few pores, just nanometers wide, in the graphene with an electron beam. The membrane is finally immersed in a salt solution that’s in contact with silver electrodes. The researchers observed dips in the current when a DNA strand passed through the pore, showing that the method could eventually be used to identify DNA bases.

May 28, 2010

Nanotech and DNA sequencing

Put the two together and you’ve got a solution for a major problem with the genome sequencing technique called nanopore translocation. And yet another application is found for graphene.

From the link:

But how do you measure the electrical properties of a single subunit among many tens or hundreds of thousands?

One of the most promising ideas is to make a tiny hole through a thin sheet of material and measure the amount of current that passes from one side of the sheet to another.

Next, pull a strand of DNA through this hole and measure the current again. Any difference must be caused by the nucleotide base that happens to blocking the hole at that moment.

So measuring the way the current changes as you pull the strand through the hole gives you a direct reading of the sequence of nucleotide bases in the strand.

Simple really. Except for one small problem. Even the thinnest films of semiconducting materials used for this process, such as silicon nitride, are between 10 and 100 times thicker than the distance between two nucleotide bases on a strand of DNA.

So when a strand of DNA passes through the hole, it’s not a single nucleotide base that blocks it but as many as 100. That makes it hard to determine the sequence from any change in the current.

Today, Grégory Schneider and buddies at the Kavli Institute of Nanoscience in The Netherlands present a solution to this problem. Instead of a conventional material, this team has used graphene, which is relatively easy to produce in sheets just a single atom thick.

Graphene is like a sheet of chicken wire made of carbon atoms. These guys have drilled holes of various diameters through just such a sheet using an electron beam to smash carbon atoms out of the structure.