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New Nanomaterials Control, Direct Light Energy

Photonics.com
Jul 2011
TORONTO, Canada, July 18, 2011 — Taking inspiration from the photosynthetic inner workings of plants, engineers have built nanoantennas that control and direct the energy absorbed from light.

"Nanotechnologists have for many years been captivated by quantum dots — particles of semiconductor that can absorb and emit light efficiently, and at custom-chosen wavelengths," said Shana Kelley, a professor at Leslie Dan Faculty of Pharmacy, the Department of Biochemistry in the Faculty of Medicine, and the Department of Chemistry in the Faculty of Arts & Science at the University of Toronto. "What the community has lacked — until now — is a strategy to build higher-order structures, or complexes, out of multiple ... types of quantum dots. This discovery fills that gap."


Tiny semiconducting nanocrystals (quantum dots) can be engineered to absorb and emit a range of light wavelengths. (Image: Argonne National Laboratory via Flickr)

The U of T researchers combined their expertise in DNA and in semiconductors to invent a generalized strategy to bind certain classes of nanoparticles to one another.

"The credit for this remarkable result actually goes to DNA: its high degree of specificity — its willingness to bind only to a complementary sequence — enabled us to build rationally engineered, designer structures out of nanomaterials," said Ted Sargent, a professor in the Edward S. Rogers Sr. Department of Electrical & Computer Engineering at U of T, who is also the Canada research chair in nanotechnology. "The amazing thing is that our antennas built themselves — we coated different classes of nanoparticles with selected sequences of DNA, combined the different families in one beaker, and nature took its course. The result is a beautiful new set of self-assembled materials with exciting properties."

Traditional antennas increase the amount of an electromagnetic wave — such as a radio frequency — that is absorbed, and then funnel that energy to a circuit. The U of T nanoantennas instead increased the amount of light that is absorbed and funneled it to a single site within their moleculelike complexes. This concept already is used in nature in light harvesting antennas, constituents of leaves that make photosynthesis efficient.

"Like the antennas in radios and mobile phones, our complexes captured dispersed energy and concentrated it to a desired location. Like the light harvesting antennas in the leaves of a tree, our complexes do so using wavelengths found in sunlight," Sargent said.

"This is a terrific piece of work that demonstrates our growing ability to assemble precise structures, to tailor their properties and to build in the capability to control these properties using external stimuli," said Paul S. Weiss, Fred Kavli Chair in NanoSystems Sciences at the University of California, Los Angeles, and director of California NanoSystems Institute.

"What this work shows is that our capacity to manipulate materials at the nanoscale is limited only by human imagination. If semiconductor quantum dots are artificial atoms, then we have rationally synthesized artificial molecules from these versatile building blocks."

Their findings are reported in the journal Nature Nanotechnology.

For more information, visit: www.utoronto.ca


GLOSSARY
electromagnetic wave
Wave of radiation identified by individual fluctuations of electric and magnetic fields.
nanotechnology
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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