Northwestern researchers assemble gold, DNA into structures that manipulate light


Colin Boyle/Daily Senior Staffer

Technological Institute. A team of McCormick professors discovered how to build structures out of gold nanoparticles and DNA.

Alane Lim, Reporter

Harry Potter fans, take note: Northwestern researchers have discovered how to build structures on surfaces out of gold nanoparticles and DNA, which could lay the groundwork for devices akin to Harry’s invisibility cloak in the future.

Led by Weinberg Prof. Chad Mirkin and McCormick Profs. Vinayak Dravid and Koray Aydin, an interdisciplinary team of scientists and engineers used DNA assembly and “top-down lithography” to organize nanoparticles in two and three dimensions, according to a news release. Nanoparticles are typically between one and 100 nanometers in size.

The study was published in the journal Science on Jan. 18.

Conventional methods have used either top-down lithography or “bottom-up” chemical methods like the DNA assembly used in the study, but not both, Aydin told the Daily. He added that the team’s approach combined both methods to achieve significant control over the resulting nanoparticle structures.

“We have a wide range of knobs we can tune,” he said, adding that the parameters they could control included size and shape of the nanoparticles, spacing between nanoparticles and DNA length.

Jarad Mason, a chemistry professor at Harvard University and former postdoctoral researcher at NU, told The Daily the team used gold nanoparticles because they interact very strongly with light. This allows them to create new materials that can manipulate light in ways that conventional materials would not be able to.

He added that DNA — which can change its structure in response to changes in the environment, such as different concentrations of ethanol — allows researchers to change how close the gold nanoparticles are to each other. When the nanoparticles are farther apart, the surface they are on appears red, turning green and then brown as they get closer together, he said.

Aydin said that the method used in the study could ultimately have applications in biosensing and metamaterials — materials not found in nature — like cloaking devices, though cloaking devices had not been investigated in the study.

“It’s really an enabling material platform that would open significant possibilities in designing optically active materials, metamaterials,” he said.

Aydin said simulations helped guide the researchers toward making particular architectures that previous researchers had not been able to make. He said the the effort relied on expertise from the three groups — Mirkin is an expert in nanoparticle synthesis and DNA assembly, Dravid in lithography and Aydin in simulations and optical characterization, he said.

Mason said that with the new method, nanoparticles of different sizes and shapes could be stacked together with precision.

“Architecture is everything when designing new materials, and we now have a new way to precisely control particle architectures over large areas,” Mirkin said in the release. “Chemists and physicists will be able to build an almost infinite number of new structures with all sorts of interesting properties.”

Qing-Yuan Lin, a former graduate student who worked on the project, compared the architectures to houses. Just like a house is made up of different building blocks like bricks, doors and other components, he said, the architectures can be composed of nanoparticles of different shapes and sizes.

“If you want to build a building you can’t only have one type of block,” he said. “Different building blocks can serve different functions because they have different properties.”

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