Technische Universitaet Muenchen – In the human body genetic information is encoded in double-stranded deoxyribonucleic acid building blocks, the so-called DNA. Using artificial DNA molecules, an international team of scientists headed by the Cluster of Excellence Nanosystems Initiative Munich (NIM) has produced nanostructured materials that can be used to modify visible light by specification.
They will try to use this DNA Origami to make metamaterial Super lenses
By combining theoretical calculations and the possibilities of DNA origami, the researchers are now able to produce nano-optical materials with precisely specified characteristics. Professor Tim Liedl describes the path the research might follow: “We will now investigate whether we can use this method to influence the refraction index of the materials we manufacture. Materials with a negative refractive index could be used to develop novel optical lens systems – so-called super lenses.”
Right-handed and left-handed nano spiral staircases differ visibly in their interaction with circular polarized light. Photo: Tim Liedl / LMU
Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties. Particularly promising components for such materials are metal nanostructures, where structural alterations provide a straightforward means of tailoring their surface plasmon resonances and hence their interaction with light. But the top-down fabrication of plasmonic materials with controlled optical responses in the visible spectral range remains challenging, because lithographic methods are limited in resolution and in their ability to generate genuinely three-dimensional architectures. Molecular self-assembly provides an alternative bottom-up fabrication route not restricted by these limitations, and DNA- and peptide-directed assembly have proved to be viable methods for the controlled arrangement of metal nanoparticles in complex and also chiral geometries. Here we show that DNA origami enables the high-yield production of plasmonic structures that contain nanoparticles arranged in nanometre-scale helices. We find, in agreement with theoretical predictions, that the structures in solution exhibit defined circular dichroism and optical rotatory dispersion effects at visible wavelengths that originate from the collective plasmon–plasmon interactions of the nanoparticles positioned with an accuracy better than two nanometres. Circular dichroism effects in the visible part of the spectrum have been achieved by exploiting the chiral morphology of organic molecules and the plasmonic properties of nanoparticles or even without precise control over the spatial configuration of the nanoparticles. In contrast, the optical response of our nanoparticle assemblies is rationally designed and tunable in handedness, colour and intensity—in accordance with our theoretical model.
Assembly of DNA origami gold nanoparticle helices and principle of circular dichroism. Left- and right-handed nanohelices (diameter 34 nm, helical pitch 57 nm) are formed by nine gold nanoparticles each of diameter 10 nm that are attached to the surface of DNA origami 24-helix bundles (each of diameter 16 nm).
They have now succeeded in building nanoparticles using optically active DNA building blocks that can be used to modify light in very specific ways.
Coupling light and nanostructures may help significantly reduce the size of optical sensors for medical and environmental applications, while at the same time making them more sensitive. However, the size of a light wave stretching out over 400 to 800 nanometers is gigantic in comparison to nanostructures of only a few nanometers. Yet in theory, when tiniest structures work together in very specific ways, even small objects can interact very well with light. Unfortunately it is not possible to produce the requisite three-dimensional structures with nano-scale precision in sufficient quantities and purity using conventional methods.
“With DNA origami, we have now found a methodology that fulfills all of these requirements. It makes it possible to define in advance and with nanometer precision the three-dimensional shape of the object being created,” says Professor Friedrich Simmel, who holds the Chair for Biomolecular Systems and Bionanotechnology at the TU Muenchen. Programmed solely using the sequence of basic building blocks, the nano-elements fold themselves into the desired structures.” Friedrich Simmel’s team successfully built nano spiral staircases 57 nanometers high and 34 nanometers in diameter with 10 nanometer gold particles attached at regular intervals.
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