Featured Research

from universities, journals, and other organizations

After Quantum Dots, Now Come Glowing 'Cornell Dots,' For Biological Tagging, Imaging And Optical Computing

Date:
May 20, 2005
Source:
Cornell University News Service
Summary:
By surrounding fluorescent dyes with a protective silica shell, Cornell University researchers have created fluorescent nanoparticles cheaper and more chemically inert than quantum dots, with possible applications in displays, biological imaging, optical computing, sensors and DNA chips.

Schematic representation of a Cornell Dot, with several molecules of a fluorescent rhodamine dye encapsulated in the center. The dye has been modified with a group that links to the encapsulating silicon.
Credit: Courtesy of Ulrich Wiesner / Copyright Cornell University

ITHACA, N.Y. -- Move over, quantum dots. Make way for the new kids on the block brightly glowing nanoparticles dubbed "Cornell dots."

Related Articles


By surrounding fluorescent dyes with a protective silica shell, Cornell University researchers have created fluorescent nanoparticles with possible applications in displays, biological imaging, optical computing, sensors and microarrays such as DNA chips. These are all applications for which quantum dots have been used or are being considered. But the new Cornell nanoparticles offer an appealing alternative because of their greater chemical inertness and reduced cost.

"People have done superb experiments with quantum dots that were not previously possible," says Ulrich Wiesner, Cornell associate professor of materials science and engineering. "Hopefully Cornell dots will serve the same purpose and offer new possibilities." There are also some interesting physics questions about how the new dots work, he adds.

Since optical microscopes can't resolve individual molecules, and electron microscopes can't be used on living organisms, biologists often tag organic molecules with fluorescent dyes in order to track their movements through biological processes, such as the action of enzymes inside a living cell. While it can't see the molecules, an optical microscope can track the bright light given off by the dye.

Quantum dots -- which have been used for the same purpose -- are tiny particles of semiconductors such as cadmium selenide that behave as if they were individual atoms: They can absorb light energy, kicking their internal electrons up to higher energy levels, then release the energy by emitting light. A quantum dot fluoresces much more brightly than a dye molecule, making it a desirable marker.

Cornell dots, also known as CU dots, are nanoparticles consisting of a core about 2.2 nanometers (nm) in diameter containing several dye molecules, surrounded by a protective silica shell, making the entire particle about 25 nm in diameter. The researchers call this a "core-shell architecture." (A nanometer is one-billionth of a meter, about three times the diameter of a silicon atom.)

Like quantum dots, CU dots are many times brighter (20-30 times) than single dye molecules in solution and resist "photobleaching," a process by which dyes in solution rapidly lose their fluorescence. CU dots can be made with a wide variety of dyes, producing a large assortment of colors.

The manufacture of CU dots and early experiments with them are described in a paper, "Bright and Stable Core-Shell Fluorescent Silica Nanoparticles," in the journal Nano Letters (Vol. 5, No. 1) by Wiesner and his Cornell colleagues Hooisweng Ow, Daniel R. Larson, Mamta Srivastava, Barbara A. Baird and Watt W. Webb.

Unlike quantum dots, CU dots are mostly chemically inert. The silica shell is silicon dioxide -- essentially glass. For use as biological markers, quantum dots are encased in a polymer shell -- a process that adds to their already high manufacturing cost. Quantum dots also contain heavy metals like cadmium that can leach through the polymer shell and disrupt the chemistry being observed.

However, Wiesner says, "Silica is benign, cheap and easy to attach, and it is totally compatible with silicon manufacturing technology. That opens enormous possibilities in the life sciences and in information technology."

The Cornell researchers tested the use of CU dots as biological markers by attaching an antibody, immunoglobin E (IgE), and observing how this combination attached to cell receptors on leukemia mast cells.

The dots also offer an intriguing physics question: Why do they fluoresce so brightly? In effect, the whole is brighter than the sum of its parts. "We have this enormous brightness, and we don't know exactly where it's coming from," Wiesner says. Several explanations have been offered. One is that the silicon shell protects the dye molecules from the solvent. A second is that dye molecules floating free can lose energy by actions other than emitting photons, but in the packed core of the particle those other actions are diminished.

The dots were created by Ow, then Wiesner's graduate student. Webb, the S.B. Eckert Professor in Engineering, and Larson, a graduate student in applied and engineering physics now at Albert Einstein College of Medicine, studied their photophysical properties. Baird, director of the Cornell Nanobiotechnology Center, and Srivastava, a postdoctoral researcher, studied the dots as labels on living cells.

The research was supported by the National Science Foundation, the state of New York and Phillip Morris USA. Quantum Dot Corp. supplied quantum dots used for comparison.


Story Source:

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


Cite This Page:

Cornell University News Service. "After Quantum Dots, Now Come Glowing 'Cornell Dots,' For Biological Tagging, Imaging And Optical Computing." ScienceDaily. ScienceDaily, 20 May 2005. <www.sciencedaily.com/releases/2005/05/050520175142.htm>.
Cornell University News Service. (2005, May 20). After Quantum Dots, Now Come Glowing 'Cornell Dots,' For Biological Tagging, Imaging And Optical Computing. ScienceDaily. Retrieved November 28, 2014 from www.sciencedaily.com/releases/2005/05/050520175142.htm
Cornell University News Service. "After Quantum Dots, Now Come Glowing 'Cornell Dots,' For Biological Tagging, Imaging And Optical Computing." ScienceDaily. www.sciencedaily.com/releases/2005/05/050520175142.htm (accessed November 28, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Friday, November 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA's First 3-D Printer In Space Creates Its First Object

NASA's First 3-D Printer In Space Creates Its First Object

Newsy (Nov. 26, 2014) The International Space Station is now using a proof-of-concept 3D printer to test additive printing in a weightless, isolated environment. Video provided by Newsy
Powered by NewsLook.com
Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Bolivian Recycling Initiative Turns Plastic Waste Into School Furniture

Reuters - Innovations Video Online (Nov. 26, 2014) Innovative recycling project in La Paz separates city waste and converts plastic garbage into school furniture made from 'plastiwood'. Tara Cleary reports. Video provided by Reuters
Powered by NewsLook.com
Blu-Ray Discs Getting Second Run As Solar Panels

Blu-Ray Discs Getting Second Run As Solar Panels

Newsy (Nov. 26, 2014) Researchers at Northwestern University are repurposing Blu-ray movies for better solar panel technology thanks to the discs' internal structures. Video provided by Newsy
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. Video provided by Newsy
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