Practitioners of traditional origami can fold tiny, colorful bits of paper and make high art. But the growing group of scientists who practice DNA origami can fold genetic code itself, creating intricate nanoscopic materials with incredible properties.
In a new study out this week, scientists used the technique to create tiny structures that can manipulate light by absorbing it differently depending upon how the materials form—which could someday create lenses of amazing power. Previous research has shown that DNA origami can create nanobots that potentially could target and kill cancer cells one day.
So how are researchers around the world bending the very shape of DNA to their will?
Let's go back to biology-class basics. DNA is made up of four bases: adenine, thymine, guanine, and cytosine (A, T, C, and G) that bond in pairs. A connects to T; C connects to G. Scientists can take advantage of those relationships to create self-assembling materials. Shawn Douglas, a biophysicist at Harvard University's Wyss Institute for Biologically Inspired Engineering, says that because those DNA bases will naturally seek out their counterpart, all a scientist needs to do is write up a blueprint. "Since the shape in encoded in the building material, we don't have to assemble each one," he says.
With DNA origami, the blueprint involves two main components: one long strand of DNA called a scaffold that contains around 7000 bases, and smaller staple strands that have between 30 and 50 bases. As the bases that make up these staples bond to the bases on the scaffold, they fold the scaffold into the appropriate shape (the folding is why it's called origami). If necessary, scientists can even design the staples to have chemical attachments where the researchers can add other materials.
A researcher sends the blueprints for the staples and scaffolds to a company that synthesizes DNA. When the scientists get the DNA strands back, they mix them together and the DNA particles assemble themselves into the desired shape. Douglas says that even in a mixture the size of a raindrop, scientists can produce anywhere from 50 billion to 100 billion DNA structures in a matter of moments. Inside the vial, the billions of strands are playing a complex game of musical chairs, with the short staple strands racing to attach to the correct spot on one of the scaffold strands before all the spots are taken.
Superlenses and Nanobots
Paul Rothemund, a research associate at CalTech, invented DNA origami six years ago in 2006, designing two-dimensional shapes like stars and smiley faces to show the range of the method. Since then, the method has become more and more popular in the field of bionanotechnology.
Rothemund says that DNA itself is "mostly good as an information storage medium," as evidenced by the incredible amount of genetic code stored in our bodies. But DNA isn't good at conducting electricity and it's not very chemically reactive, so, to use DNA origami to make new materials with useful properties, scientists must add other ingredients during the process of folding DNA.
In the study released in Nature this week, for example, scientists in Munich used DNA origami to create two kinds of cylindrical spirals with small gold pieces arranged along the edges—some that spiraled to the left, and others that spiraled to the right.
Spirals may seem like an arbitrary design choice, but they were designed with a specific function in mind. Tim Leidl, who runs the group at Munich that directed the research says, "In our case, the usefulness is that it can interact with light." In the teams' experiments, they put spirals that were all rotated in the same direction into a solution, and then found that the solutions absorbed light differently depending upon whether they contained left- or right-handed spirals. "The main importance of the work is that it shows that using self-assembly you can create materials with a predesigned function," says Anton Kuzyuk, a postdoctoral student who worked on the study.
The spiral experiment is a neat proof-of-concept for now. But in their study, the researchers speculate that future development of this idea could lead to the development of new materials with wild optical properties, such as a negative refractive index. This feature appears in no known natural materials, but scientists have shown that it's possible for engineered metamaterials, and hope that such materials could be used to develop a superlens, or a perfect lens, that would allow scientists to see objects as small as viruses. The materials could even have applications in the invisibility cloak science that's under way.
And DNA origami designs reach beyond the realm of hard physics. Just a few weeks ago, Harvard's Douglas published a paper in the journal Science that described a DNA nanorobot. The nanorobot was engineered to carry antibody fragments and could identify and destroy cancer cells in a petri dish.
While the research is a long way from being tested in humans, it's still an intriguing demonstration of what this method is capable of building—scientists are just starting to figure out what can be done with DNA origami. "DNA is a very powerful method for constructing things, as evidenced by the diversity of life," Douglas says.
Douglas is getting the next generation of scientists excited about the possibilities. Last year he started a competition called BioMod that encourages undergraduate students from around the world to spend the summer designing their own bio-nanotech project, either with DNA origami or other methods. That project is then entered into a competition at Harvard in the fall. Some of the projects from last year show paths that the field could take in the future, including DNA robots that can move along a track and respond to light, RNA drug delivery systems that can knock out targeted genes or deliver drugs to specific cells, and a DNA processor that can count.