In a huge achievement spanning both chemistry and physics, scientists have found a way to create entirely new classes of material that can bend oncoming light around them, making them appear invisible. No, that is not hyperbole, and yes, this is how the cloaking devices work in Star Trek. It is alright to be excited.
Researchers from Northwestern University combined DNA with gold nanoparticles to create optically active superlattices—structures that can be programmed to shift to any desired point on the visible color spectrum. The unprecedented technique merges elements of top-down lithography—the same process by which computer chips are made—with programmable DNA, allowing the researchers to control the properties of each individual particle, assembling them into nearly any configuration they can imagine. There is no other known technique by which such structures can be made. A paper describing the research was published in the journal Science.
“So now we have a type of architectural control where we can build crystalline-type lattices with all the defined parameters that we want,” co-author Chad Mirkin, director of the International Institute for Nanotechnology at Northwestern, told Newsweek. “We can make structures that nobody’s ever even conceived of before; this is a true man-over-nature event.”
In 1996, Mirkin and three colleagues published a paper announcing their invention of a method for programming DNA to build nanoparticles up into macroscopic materials. The idea was to develop a completely new field of chemistry, where instead of using the elements available to us from the standard periodic table we could use nanoparticles, modified with DNA, to make...whatever we want. The technical precision to integrate the components—a single particle at a time—wasn't accessible two decades ago. It is now.
With this new lithography technique, the researchers can define in the properties of the particles ahead of time, inputting the desired pattern like X and Y variables into a math equation. The particles can be reprogrammed over and over. The combinations are pretty much infinite.
The technique would be used to create metamaterials, meaning materials that don’t exist in nature. But nature itself still contains all kinds of stuff made from particles that can control their optic qualities. Chameleon skin, butterfly wings and opals all contain natural colloidal crystals that allow them to change color; their particles have evolved to be able to modulate the space between them and shift themselves into different configurations.
The DNA strands the researchers used are sensitive to environmental stimuli, meaning they can be modulated by adding certain chemical compounds that prompt them to contract or expand—drawing the particles closer together or pushing them apart—changing their optical properties like a chameleon's. The team thinks the breakthrough will lead to a surge of biological sensor technologies.
The idea of cloaking devices was popularized by Star Trek beginning with the original series in the mid-'60s, but it gained traction as a legitimate possibility in the scientific community about a decade ago. Since then, Mirkin said, there’s been an “explosion” of interest in creating what are known as negative refraction materials—materials that bend light around a structure so that you can’t see it, rendering it effectively invisible.
This new technique represents a way to not just bend the light, but block it, bounce it back, basically make it do whatever you want, so long as the nanoparticles belong to something that can be modified with DNA (like gold).
Mirkin said that the resulting metamaterials could be used to build cutting-edge sensor technologies within the next five or 10 years. As far as cloaking technology goes, it’s difficult to predict an exact timeline; since these materials have never existed before, scientists have (understandably) never considered how to use them. Mirkin guessed it’ll take about two to five years for everyone to get used to the idea and start moving to commercialization.
“Most people in the field of metamaterials haven’t even contemplated structures like this,” Mirkin said. “They can’t be made by any other techniques. This will challenge the rest of the world to think about what architectures will have desirable properties; we’re not limited anymore.”