Featured Research

from universities, journals, and other organizations

Brightening Prospects Of Using Fluorescent Nanotubes In Medical Applications

Date:
June 11, 2007
Source:
Vanderbilt University
Summary:
Researchers have removed an obstacle that has restricted fluorescent nanotubes from a variety of medical applications, including anti-cancer treatments. They describe a method that can successfully produce large batches of highly fluorescent nanotubes.

Three-dimensional molecular model of a nanotube wrapped in soap molecules.
Credit: Tobias Hertel

In a way, nanotubes are nature's smallest candles.

These tiny tubes are constructed from carbon atoms and they are so small that it takes about 100,000 laid side-by-side to span the width of a single human hair. In the last five years, scientists have discovered that some individual nanotubes are fluorescent. That is, they glow when they are bathed in light. Some glow brightly. Others glow dimly. Some glow in spots. Others glow all over.

Until now, this property has been largely academic. But researchers from the Vanderbilt Institute of Nanoscale Science and Engineering (VINSE) have removed an obstacle that has restricted fluorescent nanotubes from a variety of medical applications, including anti-cancer treatments. In a paper published online in the Journal of the American Chemical Society on June 7, they describe a method that can successfully produce large batches of highly fluorescent nanotubes.

"Nanotubes have a number of characteristics that make them particularly suitable for use as contrast agents in cells and tissues," says Tobias Hertel, the associate professor of physics who headed the research. "Now that we know how to separate out the brightest ones, I hope that researchers will begin considering ways to use them in clinical applications."

The figure of merit for fluorescence is quantum efficiency: the ratio of the number of photons of light that a device emits to the number of photons it absorbs in the process. The VINSE team reports that they can produce populations containing trillions of nanotubes with a quantum efficiency of 1 percent, a factor of 100 better than previous ensemble measurements and close to the best quantum efficiencies reported for individual nanotubes.

The methods researchers use to produce nanotubes creates soot that contains a number of different types of nanotubes: metallic, semiconducting, double-walled, single-walled, etc. Of these, only the single-walled semiconducting nanotubes, or SWNTs, are capable of producing light. Metallic nanotubes actually inhibit the brightness of their fluorescent neighbors. But it has been very difficult to separate the strongly fluorescent SWNTs from all the rest in large quantities.

Nanotube soot is insoluble in water. So researchers routinely mix it with special soap and give it a dose of ultrasound to break apart clumps of nanotubes and force them to dissolve. The result is a dark liquid that is routinely put into an ultracentrifuge that subjects them to forces a few thousand times that of gravity. Centrifuging separates out a number of gross impurities.

Hertel's team discovered that if they remove the most buoyant layer from the centrifuge, let it set for a while and then put it back in the ultracentrifuge for another 12 hours, the liquid separates into a number of distinct layers. The topmost layer has a purple color and, when analyzed, proves to contain a surprisingly uniform population of the brightest nanotubes.

The researchers had expected this approach to boost the quantum efficiency by five to ten times. The fact that the improvement was considerably larger — 20 to 100 times — came as a pleasant surprise.

"Quantum efficiency is critical, but there are several other factors that make nanotubes particularly well suited for use in living systems," says Hertel. These factors include:

Nanotubes emit light in a very narrow range of wavelengths, or colors. This makes it easier to pick out their signal against background noise. Furthermore, they produce light in a part of the spectrum — the near infrared where skin and other tissue is transparent — that allows the nanotube light to stand out.

Nanotubes are made entirely from graphitic carbon, which is non-toxic and, at least so far, experiments that have been done indicate that they do not damage living cells. By comparison, quantum dots, which are a popular alternative fluorescent tagging technology, are made from the elements cadmium and selenium that are toxic at relatively low levels and so have not been approved for clinical applications.

Nanotube fluorescence is extremely stable and can last for months. Fluorescent proteins — widely used for imaging living systems — begin fading within a few hours. Quantum dots last several days before degrading.

Hertel's team is currently working on the next step necessary for many biomedical uses: finding a way to attach molecules to the surface of the nanotubes that will allow them to bind to specific biological targets. The trick is to do so without dimming or extinguishing the nanotubes' delicate fluorescence.

An example of the possible medical applications of nanotube fluorescence is a collaboration that Hertel and Associate Professor of Biomedical Research Duco Jansen are planning. Jansen has been pursuing research that uses gold nanoclusters to burn away cancer cells. He has developed a selective method for attaching the gold clusters to the surface of tumors and then exposing them to wavelengths of light that cause them to grow hot enough to destroy nearby cells. The approach has one drawback: He doesn't have an easy way to identify the locations where the clusters attach. Nanotubes should work as well as gold clusters as microscopic blow torches while their fluorescence should make them easy to locate. At least that is the hypothesis the researchers hope to test.

Hertel's co-authors on the paper are Vanderbilt graduate student Jared Crochet and Michael Clemens, an undergraduate student from Brigham Young University. The research was funded by grants from the American Chemical Society and the National Science Foundation.


Story Source:

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


Cite This Page:

Vanderbilt University. "Brightening Prospects Of Using Fluorescent Nanotubes In Medical Applications." ScienceDaily. ScienceDaily, 11 June 2007. <www.sciencedaily.com/releases/2007/06/070607171032.htm>.
Vanderbilt University. (2007, June 11). Brightening Prospects Of Using Fluorescent Nanotubes In Medical Applications. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2007/06/070607171032.htm
Vanderbilt University. "Brightening Prospects Of Using Fluorescent Nanotubes In Medical Applications." ScienceDaily. www.sciencedaily.com/releases/2007/06/070607171032.htm (accessed July 28, 2014).

Share This




More Matter & Energy News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. 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