Diamond glitter: a play of colors with artificial DNA crystals

• With this method, they have created a new approach for manufacturing semiconductors for visible light
• The new photonic crystals could play an important role for applications in data processing, energy harvesting, and quantum technology

The shimmering of butterfly wings in bright colors does not emerge from pigments. Rather, it is photonic crystals that are responsible for this play of light. Their periodic nanostructure allows light at certain wavelengths to pass through while reflecting other wavelengths. This causes the wing scales, which are in fact transparent, to appear so magnificently colored. Artificially manufactured photonic crystals allow the development of “solar cells with higher efficiency, innovative optical waveguides, and materials for quantum communication. However, they have been very laborious to manufacture to date,” explains Dr. Gregor Posnjak, who is a physics postdoc in the research group of Tim Liedl, professor at LMU and member of the “e-conversion” Cluster of Excellence. The team’s results have now been published in the journal Science.

In contrast to lithographic techniques, the LMU team uses a method called DNA origami to design and synthesize building blocks, which then self-assemble into a specific lattice structure. “It’s long been known that the diamond lattice theoretically has an optimal geometry for photonic crystals,” explains Tim Liedl. “In diamonds, each carbon atom is bonded to four other carbon atoms. Our challenge consisted in enlarging the structure of a diamond crystal by a factor of 500, so that the spaces between the building blocks correspond with the wavelength of light.” Posnjak adds: “We increased the periodicity of the lattice to 170 nanometers by replacing the individual atoms with larger building blocks – in our case, through DNA origami.”

The perfect molecule folding technique

What sounds like magic is actually a specialty of the Liedl group, one of the world’s leading research teams in DNA origami and self-assembly. For this purpose, the scientists use a long, ring-shaped DNA strand and a set of short DNA staples. The latter control the folding of the longer DNA strand into virtually any shape – akin to origami masters, who fold pieces of paper into intricate objects.

The finished DNA origami crystals are deposited on a substrate. A team led by Professor Ian Sharp from the Walter Schottky Institute at the Technical University of Munich (TUM) is then able to coat the DNA origami crystals with individual atomic layers of titanium dioxide. “The DNA origami diamond lattice serves as scaffolding for titanium dioxide, which, on account of its high index of refraction, determines the photonic properties of the lattice. After coating, our photonic crystal does not allow UV light with a wavelength of about 300 nanometers to pass through, but rather reflects it,” explains Posnjak. The wavelength of the reflected light can be controlled via the thickness of the titanium dioxide layer.

DNA origami could boost photonics

For photonic crystals that work in the infrared range, classic lithographic techniques are suitable but laborious and expensive. In the wavelength range of visible and UV light, lithographic methods have not been successful to date. “Consequently, the easier manufacturing process using the self-assembly of DNA origami in an aqueous solution offers a powerful alternative for producing structures in the desired size cost-effectively and in larger quantities,” says Prof. Tim Liedl. He is convinced that the unique structure with its large pores, which are chemically addressable, will stimulate further research – for example, in the domain of energy harvesting and storage. In the same issue of Science, a collaboration led by prof. Petr Šulc of Arizona State University and TUM presents a theoretical framework for designing diverse crystalline lattices from patchy colloids, and experimentally demonstrates the method by utilizing DNA origami building blocks to form a pyrochlore lattice, which potentially also could be used for photonic applications.

Paper:
Gregor Posnjak, Xin Yin, Paul Butler, Oliver Bienek, Mihir Dass, Seungwoo Lee, Ian D. Sharp, Tim Liedl:
Diamond lattice photonic crystals assembled from DNA origami
Science 2024

Contact:
Dr. Gregor Posnjak
Research Group on Molecular Self-Assembly and Nanoengineering
Faculty of Physics and Center for NanoScience (CeNS)
Ludwig-Maximilians-Universität München
Geschwister-Scholl-Platz 1
80539 Munich, Germany
Email: gregor.posnjak@physik.lmu.de

Prof. Tim Liedl
Research Group on Molecular Self-Assembly and Nanoengineering
Faculty of Physics and Center for NanoScience (CeNS)
Ludwig-Maximilians-Universität München
Geschwister-Scholl-Platz 1
80539 Munich, Germany
Email: tim.liedl@physik.lmu.de
Web: https://www.softmatter.physik.uni-muenchen.de/liedl_group/index.html