Featured Research

from universities, journals, and other organizations

'Strained' Quantum Dots Show New Optical Properties

Date:
December 14, 2008
Source:
Emory University
Summary:
The first generation of quantum dots were made from the toxic heavy metal cadmium and had emission wavelengths, and colors, determined by their size. "Lattice strain" created by layers of different semiconductor materials allows the color of quantum dots to be tuned independent of size. Small enough to pass through the kidneys if administered systemically, the new quantum dots are expected to be useful for cancer detection and possibly in solar energy conversion.

Quantum dots, tiny luminescent particles made of semiconductors, hold promise for detecting and treating cancer earlier. However, if doctors were to use them in humans, quantum dots could have limitations related to their size and possible toxicity.

Scientists at Emory University and the Georgia Institute of Technology have found a way around those limitations by exploiting a property of semiconductors called "lattice strain." By layering materials with different chemical compositions on top of each other, the researchers can create particles with new optical properties.

A description of the "strain-tuned" particles is published in the journal Nature Nanotechnology.

"The first generation of quantum dots had optical properties that could be tuned by their size," says senior author Shuming Nie, PhD, a professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. "We have discovered another way to tune quantum dots' properties: by modulating lattice strain."

In addition to their expected utility in biomedical imaging, the new type of quantum dots could find use in optoelectronics, advanced color displays, and more efficient solar panels, Nie adds.

A mismatch between the lattices of the semiconductors making up the inner core and outside shell of the particle creates strain: the core is squeezed and the shell is stretched. This physical strain changes the energies, and wavelengths, of the light produced by the quantum dot.

Previous quantum dots contained cadmium, a toxic heavy metal. Strain-tuned quantum dots can be made mostly of the less toxic elements zinc and selenium, although some cadmium remains at the core of the particle. The particles can be between four and six nanometers wide.

Adding layers of zinc and selenium on top of a cadmium and tellurium core increases the wavelength of light produced as fluorescence by the quantum dots, Nie's team shows. As the core becomes smaller, the shift in the fluorescence wavelength produced by the zinc-containing layers becomes larger.

Strain-tuned quantum dots can be made that emit light at wavelengths in the near-infrared range while remaining small in size. Near-infrared wavelengths around 750 nanometers represent a "clear window" where the human body is relatively transparent, says Andrew Smith, PhD, a postdoctoral fellow in Nie's group and the first author of the paper.

While the newer strain-tuned quantum dots have not been tested in living animals or people, they could probably pass through the kidneys, meaning less toxicity, if they are less than five nanometers in diameter, Smith remarks.

"Using near-infrared wavelengths, there's less difficulty in seeing through the body's tissues," he continues. "Older quantum dots that emit in the near-infrared range are rod-shaped and large enough to get trapped in the kidneys, while smaller particles can both clear the kidneys and have less of a tendency to bind proteins in the blood."

"Core-shell nanocrystals are all expected to have some lattice mismatch between the core and the shell, so the strain effect is a general phenomenon," Nie says. "But this effect was not well understood in the past, and was often not taken into consideration. Our work shows that lattice strain is another key factor that must be considered, in addition to particle size and composition."

The National Institutes of Health, the Department of Energy and the Georgia Cancer Coalition funded the research.


Story Source:

The above story is based on materials provided by Emory University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Smith, A.M., Mohs, A.M and Nie, S. Tuning the optical and electronic properties of colloidal nanocrystals by lattice strain. Nature Nanotechnology, December 2008

Cite This Page:

Emory University. "'Strained' Quantum Dots Show New Optical Properties." ScienceDaily. ScienceDaily, 14 December 2008. <www.sciencedaily.com/releases/2008/12/081207133751.htm>.
Emory University. (2008, December 14). 'Strained' Quantum Dots Show New Optical Properties. ScienceDaily. Retrieved April 17, 2014 from www.sciencedaily.com/releases/2008/12/081207133751.htm
Emory University. "'Strained' Quantum Dots Show New Optical Properties." ScienceDaily. www.sciencedaily.com/releases/2008/12/081207133751.htm (accessed April 17, 2014).

Share This



More Matter & Energy News

Thursday, April 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Small Reactors Could Be Future of Nuclear Energy

Small Reactors Could Be Future of Nuclear Energy

AP (Apr. 17, 2014) After the Fukushima nuclear disaster, the industry fell under intense scrutiny. Now, small underground nuclear power plants are being considered as the possible future of the nuclear energy. (April 17) Video provided by AP
Powered by NewsLook.com
Honda's New ASIMO Robot, More Human-Like Than Ever

Honda's New ASIMO Robot, More Human-Like Than Ever

AFP (Apr. 17, 2014) It walks and runs, even up and down stairs. It can open a bottle and serve a drink, and politely tries to shake hands with a stranger. Meet the latest ASIMO, Honda's humanoid robot. Duration: 00:54 Video provided by AFP
Powered by NewsLook.com
German Researchers Crack Samsung's Fingerprint Scanner

German Researchers Crack Samsung's Fingerprint Scanner

Newsy (Apr. 16, 2014) German researchers have used a fake fingerprint made from glue to bypass the fingerprint security system on Samsung's new Galaxy S5 smartphone. Video provided by Newsy
Powered by NewsLook.com
Porsche CEO Says Supercar Is Not Dead: Cue the Spyder 918

Porsche CEO Says Supercar Is Not Dead: Cue the Spyder 918

TheStreet (Apr. 16, 2014) The Porsche Spyder 918 proves that, in an automotive world obsessed with fuel efficiency, the supercar is not dead. Porsche North America CEO Detlev von Platen attributes the brand's consistent sales growth -- 21% in 2013 -- with an investment in new technology and expanded performance dynamics. The hybrid Spyder 918 has 887 horsepower and 944 lb-ft of torque, but it can run 18 miles on just an electric charge. The $845,000 vehicle is not a consumer-targeted vehicle but a brand statement. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins