Munich researchers use DNA to design novel nano-scale structures with special optical properties

The team used a recently designed technique, called "DNA origami", to build a nano-scale structure resembling a staircase using DNA building blocks, which were modified to interact with light in specific ways. Their results promises a new era in the design of sensors and other applications in medical and environmental technology.

Back in 2006 a new, an exciting new technique was presented to the world, which allowed to give DNA various shapes and patterns, somewhat like what people do with paper when making origami figures. The technique, commonly known as DNA origami, was described in a Nature paper (doi:10.1038/nature04586) where it was used to create simple patterns such as words, or simple geometric figures. But this technique was much more than a tool to make figures, as it promised to become the basis of more advanced applications. However, applications using DNA origami have yet to be created.

Now, a team led by Tim Liedl of the Ludwig-Maximillians-Universität München and Friedrich Simmel of the Technische Universität München have succeeded where no-one have succeeded before. They have created one of the world's first applications of DNA origami: a structure composed of optically active DNA building blocks, which is able to modify light in specific ways.

Well, as you may remember from highschool physics, light is an electromagnetic wave and interacts with the electrons of whatever material where it lands, and in the case of this study light is interacting with custom made metallic nanoparticles. "The electrons start to oscillate in response to the light wave. In our case, the particles are arranged in helices and the oscillations of the electrons in the particles communicate with each other. It turns out that this collective motion leads to a strong absorption of certain components of the light wave (depending on the color and "polarization")." The key to make this idea work was to have a technique that will allow precise manipulations at the nano scale, the level of DNA molecules and such. Now, back to highschool, remember DNA from Biology class? It is the central molecule in all cells, and it is composed of four bases, ATGC, which pair in specific ways (A with T, G with C). This study takes advantage of this basic property of DNA and from the novel "DNA origami" technique. Dr. Simmel explains. "We used the novel "origami" assembly method to produce the helices. In origami, we use the same type of "recognition interaction" (e.g. how the DNA bases match to each other) to make large molecular structures in which many of these double helices are connected together. Because we know the structure of DNA (and origami) extremely well, we can use these structures to assemble the nanoparticles as required to produce the optical effect described above.

Mostly, it opens up the road for upcoming applications for the "DNA origami" technique. As Dr. Simmel explains "For the DNA nanotechnology field, this work is interesting as it shows that the exciting DNA origami technique is starting to generate "real-world applications" (if you wish to call that so), which is extremely important for the further establishment and maturation of this field of research." Applications include building super lenses, which are not affected by the so-called "difraction limit" which is a physical limitation that affects the maxium possible resolution of optical imaging systems, such as microscopes, telescopes or cameras, can reach (read more at http://en.wikipedia.org/wiki/Diffraction_limit).

Dr. Simmel also talks about other applications. "People hope to make miniaturized optical waveguides out of such structures, nanoantenna systems (potentially for artificial photosynthesis), or even something funny as the so-called "negative refractive index"."