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Researchers Create New Classes of Optical Materials and Devices
April 11, 2018

Northwestern University researchers have developed a first-of-its-kind technique for creating entirely new classes of optical materials and devices that could lead to light bending and cloaking devices.

Using DNA as a key tool, the interdisciplinary team took gold nanoparticles of different sizes and shapes and arranged them in two and three dimensions to form optically active superlattices. Structures with specific configurations could be programmed through choice of particle type and both DNA-pattern and sequence to exhibit almost any color across the visible spectrum, the scientists report.

“Architecture is everything when designing new materials, and we now have a new way to precisely control particle architectures over large areas,” said Chad A. Mirkin, the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern. “Chemists and physicists will be able to build an almost infinite number of new structures with all sorts of interesting properties. These structures cannot be made by any known technique.”

The technique combines an old fabrication method — top-down lithography, the same method used to make computer chips — with a new one — programmable self-assembly driven by DNA. The Northwestern team is the first to combine the two to achieve individual particle control in three dimensions.

The study, “Building Superlattices from Individual Nanoparticles via Template-Confined DNA-Mediated Assembly,” was published online by the journal Science. Prof. Mirkin and Profs. Vinayak P. Dravid, the Abraham Harris Professor of Materials Science and Engineering, and Koray Aydin, assistant professor of electrical engineering and computer science, all faculty members in Northwestern’s McCormick School of Engineering, are co-corresponding authors. Qing-Yuan Lin, Jarad A. Mason and Zhongyang Li are first authors of the study.

The researchers used a combination of numerical simulations and optical spectroscopy techniques to identify particular nanoparticle superlattices that absorb specific wavelengths of visible light. The DNA-modified nanoparticles — gold in this case — are positioned on a pre-patterned template made of complementary DNA. Stacks of structures can be made by introducing a second and then a third DNA-modified particle with DNA that is complementary to the subsequent layers.

In addition to being unusual architectures, these materials are stimuli-responsive: the DNA strands that hold them together change in length when exposed to new environments, such as solutions of ethanol that vary in concentration. The change in DNA length, the researchers found, resulted in a change of color from black to red to green, providing extreme tunability of optical properties.

“Tuning the optical properties of metamaterials is a significant challenge, and our study achieves one of the highest tunability ranges achieved to date in optical metamaterials,” said Prof. Aydin. “Our novel metamaterial platform — enabled by precise and extreme control of gold nanoparticle shape, size and spacing — holds significant promise for next-generation optical metamaterials and metasurfaces.”

The Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences and the Air Force Office of Scientific Research supported the research.

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