Human World

Scientists build tiny antenna that captures light

The story is like something out of a science fiction novel: researchers at the University of Toronto have used a combination of synthesized DNA and semiconductors to create a nano-scale antenna that harnesses light. It’s an innovation that could, one day, revolutionize the solar power industry. That’s according to University of Toronto researcher Ted Sargent, co-inventor of this special antenna, and professor of nanotechnology at the University of Toronto. His work appeared in the journal Nature Nanotechnology on July 10, 2011.

What we did was created an antenna that grabs sunlight, and then we funneled all of the energy that we captured from the light and funneled it all to one site, to one nanoscale location.

That is, to a very, very small speck in the center of a microscopic antenna.

Image Credit: Courtesy of Edward Sargent

The potential of these materials, is that once we can figure out how to translate them from materials just in solution to being a device, you could potentially make solar cells that are large in area, low in cost, and by funneling the energy towards a particular site, a particular circuit, it could aid in making these devices more and more efficient.

Dr. Sargent explained that the antenna he helped create doesn’t look like your typical TV antenna. It’s a miniscule antenna that’s made up of microscopic semiconductors that appear as colored dots; these dots are arranged in a cross-like shape (see picture). These dots are made of silicon, typically. And they’re held together by DNA – the same kind of DNA that we have in each of our cells.

Image Credit: Courtesy of Edward Sargent

DNA is something you can synthesize in a lab, and you can program exactly the sequence that you want it to have … And the DNA was designed to have two regions. One that was prone to stick to the semiconductors, and the other region which was able to stick to other DNA.

Because it contains DNA, this antenna can, with a little startup help, self-assemble. But Dr. Sargent clarified that the truly functional part of this solar antenna isn’t the DNA, but the dots the DNA is holding together. These dots reflect certain colors, and it’s the pattern of these colors that allow light to flow into and collect in one central dot. He explained that he built this cross-shaped antenna using three “tiers” of colors: green, yellow and red. Sargent placed green dots in the outside portion of the cross. Closer to the center, he put yellow dots. And smack dab in the middle: a single red dot.

All of the sun-energy the antenna collected wound up being funneled into that red dot. Why? The concept Dr. Sargent explains is a little complicated, but it’s rooted in the idea that green light is more intense – brighter, let’s say – than red light.

And so what we had built was a structure which from an energetic point of view, much like the way balls roll down hills, electrons inside this structure would want to roll from the green to the yellow, and the yellow to the red. The green particles absorbed green light, turned it into energetic electrons which rolled downhill through the yellows towards the reds. The yellows absorbed yellow light, and funneled that energy towards the reds. But what that meant was a kind of multiplier effect. We ended up concentrating, or funneling, all of the energy from this much larger structure into this nanometer-sized receiver.

Image Credit: Johns Hopkins University

Dr. Sargent added that most of us witness this kind of light-funneling every day, without knowing it. Plants absorb light using a similar kind of antenna, he said. (Sargent noted that he realized this similarity after the experiment, not before.)

He said plants have special cells that funnel light to exactly where it’s needed – to cells that convert sunlight into energy, inside the plant. Without this, plants would collect sunlight too slowly – they wouldn’t be able to get the food they needed quickly enough. So it could be that solar panels of the future will be a little like giant, ultra-efficient, manmade leaves.

What are your thoughts? An EarthSky co-worker said a self-assembling solar antenna built with DNA sounded a little scary. Or is it just science-fiction cool?

Bottom line: In a paper published in the journal Nature Nanotechnology on July 10, 2011, researchers at the University of Toronto revealed that they used a combination of synthesized DNA and semiconductors to create a tiny antenna that harnesses light.

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July 14, 2011
Human World

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Beth Lebwohl

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