Imagine a yellow smiley face. Now imagine 50 billion smiley faces floating in a single drop of water. That's what scientists have made using a new technique for building super-tiny shapes using the familiar double helix of DNA.
DNA holds our genetic code, and geneticists have studied it for decades. They have developed all kinds of tools to synthesize and manipulate this molecule. About 20 years ago, a researcher named Ned Seeman at New York University realized that scientists should be able to use all that's known about DNA to help them build nano-scale shapes that normally would be hard to engineer.
Since then, Seeman and other chemists have shown that they can use DNA to build really simple shapes such as cubes or octahedrons that are 1,000 times thinner than a human hair. They've done it by laboriously designing small snippets of DNA that will hook themselves up into the desired form.
But a new method for building things with DNA is so much faster and easier that even a high school student could think up a shape and then make a DNA version within a week, says Paul Rothemund, who came up with the idea at the California Institute of Technology in Pasadena.
"Even by the time I was making smiley faces, I didn't really believe that the method worked as well as it did," Rothemund says.
Rothemund's trick is this: Instead of custom-designing small snippets of DNA so that they fit together in a certain way, he borrows a single, long strand of DNA from a harmless virus.
"We take that very long strand of DNA -- it's about 7,000 letters long -- and we add to it about 200 short DNA strands that I call staples," Rothemund says.
The staples bring two distant parts of the DNA strand together so that it folds.
"We actually fold the DNA into any shape that we want," Rothemund says. "So in the case of the smiley faces that I made, I actually fold the DNA into a disk, but then leave two holes for the eyes and the mouth."
Rothemund has developed a computer program that can analyze a shape, figure out the right folding pattern, and then tell you what DNA staples you need to make that shape.
"It's really easy and fun, actually, to make whatever you want at the nano-scale. You design it in the computer, you order the DNA sequences, they come in the mail, you add a little bit of salt water, you heat it up and cool it down, and then an hour and a half later, it's ready to look at under the microscope."
In this week's issue of the journal Nature, Rothemund shows off some of his DNA art. One impressive nano-creation is a tiny map of the Americas. But the real goal of this work isn't tiny maps. Rothemund says that in the future, tiny DNA shapes could serve as scaffolds for quickly building nanostructures made of metals or other materials. Those could be useful in new kinds of electronic devices, such as faster computers.
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