DNA for Optically Active Superlattices

Researchers have developed a new method to precisely arrange nanoparticles of different sizes and shapes in two and three dimensions, resulting in optically active superlattices. (Source: NWU)

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 – with a new one – program­mable self-assembly driven by DNA. The team is the first to combine the two to achieve indi­vidual particle control in three dimen­sions. Scientists will be able to use the powerful and flexible technique to build meta­materials for a range of appli­cations including sensors for medical and environ­mental uses. 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 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 Aydin, assistant professor of electrical engi­neering and computer science at McCormick.

“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,” Aydin said. The study describes a new way to orga­nize nano­particles in two and three dimensions. The researchers used litho­graphy methods to drill tiny holes in a polymer resist, creating landing pads for nano­particle components modi­fied with strands of DNA. The landing pads are essen­tial, Mirkin said, since they keep the structures that are grown vertical.

The nano­scopic landing pads are modi­fied with one sequence of DNA, and the gold nano­particles are modified with comple­mentary DNA. By alter­nating nano­particles with complemen­tary DNA, the researchers built nano­particle stacks with tremen­dous posi­tional control and over a large area. The particles can be different sizes and shapes. “This approach can be used to build periodic lattices from opti­cally active particles, such as gold, silver and any other material that can be modified with DNA, with extra­ordinary nano­scale precision,” said Mirkin, director of North­western’s Inter­national Institute for Nano­technology. The success of the reported DNA programmable assembly required expertise with hybrid (soft-hard) materials and exquisite nano­patterning and litho­graphic capa­bilities to achieve the requisite spatial reso­lution, defi­nition and fidelity across large substrate areas. (Source: NWU)

Reference: Q.-Y. Lin et al.: Building superlattices from individual nanoparticles via template-confined DNA-mediated assembly, Science, eaaq0591 (2018); DOI: 10.1126/science.aaq0591

Link: International Inst. for Nanotechnology, Northwestern Univ., Evanston, USA

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