Nanotechnology Nanotechnology
Cadmium telluride quantum dots (red, yellow and green spheres) connected by short strands of DNA can
gather and transfer light energy from multiple wavelengths. This could lead to advanced materials for solar
cells and other optical devices.
By Tyler Irving
Posted October 2011
Molecules are often compared to children’s construction sets, where atoms of different sizes are connected by chemical bonds. Now the same principle has been applied to quantum dots and the result could lead to advances in solar cells and optical devices.
Quantum dots are crystalline nanoparticles that can absorb and reflect light at very specific frequencies based on their size. A team led by Shana Kelley and Ted Sargent at the University of Toronto has managed to connect cadmium telluride quantum dots of different sizes to each other using DNA as a linker. “DNA is inherently a very programmable material and you can define what other molecule that sequence will bind to,” says Kelley. “That allows us to build up pretty complex structures.”
The team builds up the dots using a one-pot process, where cadmium salts, tellurium salts, and DNA oligomers are all mixed together and heated to just below boiling. After a few minutes, cadmium telluride crystals begin to grow. The size of these quantum dots is controlled by terminating the reaction at the desired time. Meanwhile, the short DNA sequences start to bind to the surface. By changing the length of these sequences, the team can control how many of them attach; if the sequences are longer, there is less room and fewer of them bind.
By mixing dots of different sizes and valencies the team was able to create complex structures similar to
the way atoms assemble to build molecules. The complexes absorb light at multiple wavelengths and transfer
them to a single point, a feature that could be very useful in the solar harvesting or optical detection. “We
have lots of ideas for interesting devices, so we're in a phase of trying to get creative with what we can
build and what the assemblies should be able to do,” says Kelley. The work is published in Nature
Nanotechnology. 
Photo Credit: Bill Baker
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