Nanostructured materials built from artificial DNA molecules can modify light in very specific ways and could lead to the development of superlenses. An international team of scientists led by professor Tim Liedl of the Ludwig Maximilian University of Munich and professor Friedrich Simmel of the Technical University of Munich successfully built nano spiral staircases 57 nm high and 34 nm in diameter with 10-nm gold particles attached at regular intervals. Although chemically alike, solutions of right- and left-handed nano spiral staircases interact in specific ways with circular polarized light. The nano spiral staircases were built up using the DNA-origami method. (Image: Tim Liedl, LMU) Coupling light and nanostructures may help to significantly reduce the size of optical sensors for medical and environmental applications, while also making them more sensitive. However, the size of a light wave that stretches over 400 to 800 nm is quite large in comparison to nanostructures of only a few nanometers. Yet in theory, when the tiniest structures work together in very specific ways, even those small objects can interact well with light. Until now, it was not possible to produce the requisite 3-D structures with nanoscale precision in sufficient quantities and purity using conventional methods. “With DNA origami, we have now found a methodology that fulfills all of these requirements,” Simmel said. “It makes it possible to define in advance and with nanometer precision the three-dimensional shape of the object being created. Programmed solely using the sequence of basic building blocks, the nano-elements fold themselves into the desired structures.” Scientists from the Technical University of Munich and the Ludwig Maximilian University of Munich have succeeded in building up nano spiral staircases from artificial DNA using a technique called the DNA-origami method. The DNA strand carries nine gold particles that induce strong interactions with circular polarized visible light. (Image: Tim Liedl, LMU) Electrons on the surface of the gold particles react with the electromagnetic field of light. The small clearance between the particles ensures that the gold particles of a DNA strand work in unison, amplifying the interactions many fold. It was previously predicted by theoretical physicist Alexander O. Govorov of Ohio University in Athens that the effect should depend on the spacing, size and composition of the metal particles. The Munich physicists varied these parameters as they built the nanostructures using the DNA-origami method. Their findings confirmed that aqueous solutions of right- and left-handed nano spiral staircases differ visibly in their interactions with circular polarized light. Spiral staircases with large particles show a significantly stronger optical response than those with small particles. Fluids containing gold particles that are organized in chiral configurations exhibit designable optical activity. The gold particles are assembled with nanometer precision in space with the help of a rigid DNA origami construct.(Image: Kuzyk, Schreiber, Hohmann) They discovered also that the particle’s chemical composition plays a significant role: When the gold particles were coated with a layer of silver, the optical resonance shifted from the red to the shorter-wave blue domain. “We will now investigate whether we can use this method to influence the refraction index of the materials we manufacture,” Liedl said. “Materials with a negative refractive index could be used to develop novel optical lens systems — so-called superlenses.” The work was funded by the Volkswagen Foundation, the DFG Cluster of Excellence Nanosystems Initiative Munich and the National Science Foundation. For more information, visit: www.zv.tum.de