Molecular Origami Technique Helps Design Optically Active Materials

Published on March 17, 2012 at 5:39 AM

By Cameron Chai

A team of international researchers led by Professor Tim Liedl, a LMU physicist, has developed novel, optically active, three-dimensional structures based on the structure of DNAs. DNA strands act as scaffolds for bonding gold nanoparticles in predestined patterns.

These 3D structures are capable of customizing the properties of visible light in almost all ways. During the study, the team selected right- and left-handed helical arrays for the gold nanoparticles. It tuned the interaction between the metal nanoparticles and light by properly selecting the parameters. This molecular origami technique paves the way to develop self-assembling metamaterials and new class of lenses.

Any forms of 3D structures can be fabricated by mixing DNA strands capable of pairing with each other at designated sites. The research team created an 85-nm-long cylinder comprising localized binding sites, wherein 10-nm gold nanoparticles were bonded like a string of beads that helically wraps around the cylinder. The team is able to tailor the material’s impact on light rays travelling through it by modifying the characteristics of the water-soluble structures or altering the composition, disposition, and size of the metal particles.

For example, the arrangement of the gold nanoparticles either in right- or left-handed helices modifies the properties of the traversed light accordingly. The size of the nanoparticles has a significant impact on the level of the optical response and their accurate chemical behaviour markedly influences their interaction with the incident light.

A material’s optical activity can be characterized by using the circular dichroism phenomenon. When the optical response of a given metamaterial sample was detected at different wavelengths, the outcomes were in line with the calculations derived from a theoretical model. Therefore, the model can be utilized to design materials that alter light in particular ways. Liedl informed that the research team’s next step is to study the possibility of modulating the refractive index of the materials because materials having negative refractive index are suitable for developing innovative optical lens systems.

Source: http://www.uni-muenchen.de

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