Cloaking devices—or devices that can render an object invisible—are still mainly the stuff of science fiction. New work by researchers at Northwestern University could remove the “fiction” from the scenario with the development of a novel technique for creating new classes of optical materials for these types of devices and others that can bend light.
An interdisciplinary team from Northwestern University has used combined the use of DNA and gold nanoparticles to form optically active superlattices that for the first time can be programmed through choice of particle type and both DNA-pattern and sequence to exhibit almost any color across the visible spectrum, said Koray Adin, a professor in Northwestern’s McCormick School of Engineering and one of the researchers on the team. The invention paves the way for unprecedented control of optical properties in materials that hasn’t been achieved before, he said.
“In our study, we define the optically active structures as gold nanoparticles arranged on a surface as a multilayer fashion using DNA-assembly,” Adin explained to Design News. “The distance between nanoparticles can be tuned dynamically by changing the DNA length using a chemical solution, enabling significant control over optical properties.”
The team’s novel method will enable new optical materials based on nanoparticles—not limited to metallic particles nor found in nature--for a range of applications, including a range of sensors for medical and environmental uses, Adin said.
“Scientific applications are very broad, including bio-sensing, optical metamaterials, plasmonic devices that can concentrate light, photocatalysis, and many more,” he said.
The technique the team used combines an old fabrication method--top-down lithography, the same method used to make computer chips--with a new one; that is, programmable self-assembly driven by DNA.
The Northwestern team is the first to combine the two to achieve individual particle control in three dimensions, researchers said. This control of the geometry, shape, arrangement of nanostructures is what is key to access interesting optical properties, Adin explained.
“Conventional methods either focus on top-down lithography approaches, limiting the ability to fabricate unique nanoparticle shapes and often not yielding dynamic responses,” he said. “Bottom-up approaches like self-assembly is usually random and does not provide significant control over the arrangement of particles.
“Our method is unique in the sense that we combine best of these two fabrication techniques enabling ultimate control of size, shape, geometry, and periodicity together with dynamic control enabled by tuning the DNA-length,” Adin continued.
This precise control of nanoparticles “is a significant step toward realizing exciting metamaterial architectures simply due to precise control of nanoparticles,” he said. This is also what paves the way for the development of cloaking materials and devices, though the team didn’t specifically investigate this property in its research, Adin added.
“Our method will provide a viable platform for designing more efficient cloaking metamaterials,” he said. “Experimental demonstrations of optical cloaking devices [have been] limited due to strict requirements for refractive index distribution, which is really difficult achieve with conventional methods. With our method, one can easily design a cloaking metamaterial with precise control.”
Researchers published a paper on their work in the journal Science.
In addition the applications Adin previously mentioned, the method also can be used in material platforms such as biological and chemical sensors in which the DNA length can be tuned with the presence of biomolecules or chemical solutions, he added.
Researchers plan to continue their work to demonstrate novel metamaterial architectures that can bend, cloak, and focus light dynamically, as well as to investigate the possibility to of different types of nanoparticles such as semiconductor, magnetic, and dielectric nanoparticles to broaden the range of optical properties and dynamic control, Adin said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.