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.

Related Articles


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 October 30, 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 October 30, 2014).

Share This



More Matter & Energy News

Thursday, October 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Mind-Controlled Prosthetic Arm Restores Amputee Dexterity

Mind-Controlled Prosthetic Arm Restores Amputee Dexterity

Reuters - Innovations Video Online (Oct. 29, 2014) A Swedish amputee who became the first person to ever receive a brain controlled prosthetic arm is able to manipulate and handle delicate objects with an unprecedented level of dexterity. The device is connected directly to his bone, nerves and muscles, giving him the ability to control it with his thoughts. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Robots Get Funky on the Dance Floor

Robots Get Funky on the Dance Floor

AP (Oct. 29, 2014) Dancing, spinning and fighting robots are showing off their agility at "Robocomp" in Krakow. (Oct. 29) Video provided by AP
Powered by NewsLook.com
Saharan Solar Project to Power Europe

Saharan Solar Project to Power Europe

Reuters - Business Video Online (Oct. 29, 2014) A solar energy project in the Tunisian Sahara aims to generate enough clean energy by 2018 to power two million European homes. Matt Stock reports. Video provided by Reuters
Powered by NewsLook.com
Lowe's Testing Robot Sales Assistants in California Store

Lowe's Testing Robot Sales Assistants in California Store

Buzz60 (Oct. 29, 2014) Lowe’s is testing out what it’s describing as a robotic shopping assistant in one of its Orchard Supply Hardware Stores in California. Jen Markham explains. Video provided by Buzz60
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:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

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