Scientists discover new method for creating high-yield single-walled carbon nanotubes

carbon nanotubes

Cousins of the 1996 Nobel Prize-winning buckyball, carbon nanotubes have taken the nanotechnology industry by storm. Exhibiting extraordinary strength, flexibility and unique electrical, mechanical and optical properties, these hollow microscopic fibers are being integrated into numerous electronic and biological products—high-performance computer chips, combat jackets, bomb detectors and drug delivery devices for the treatment of diseases. Pushing the field one step further, scientists at Stanford University have devised a novel method for growing vertical single-walled carbon nanotubes (SWNTs) on a large scale, a feat that has eluded researchers until now.

By modifying the industry's standard approach to producing carbon-based materials—plasma-enhanced chemical vapor deposition (PECVD)—they achieved ultra-high-yield growth of SWNTs, thus increasing their application into commercial products. They report their research in the Oct. 26 issue of Proceedings of the National Academy of Sciences.

Carbon nanotubes are cylindrical molecules 2 nanometers in diameter—more than 10,000 times smaller than the width of a human hair. Since their discovery in 1991, multi-walled carbon nanotubes have been easily synthesized using several methods. Yet, large-scale production of smaller single-walled nanotubes into ordered films has remained intangible.

Given widespread commercial use of the PECVD method for economical, robust production of various materials by the semiconductor industry, scientists hoped to harness this same method for generating high-quality single-walled nanotubes. PECVD works by exposing substrates densely seeded with catalytic particles to a hydrocarbon gas such as methane, which should theoretically produce a plush carpet of carbon nanotubes. Previous attempts, however, have generated only sparse and inefficient synthesis of SWNTs.

Hongjie Dai, associate professor of chemistry, and his colleagues discovered the key component to attaining single-walled fibers—adding oxygen to the reaction.

"There is a dilemma here," Dai said. "What we found is that the carbon atoms are good and needed for nanotube growth, but the hydrogen atoms are bad. The carbon atoms try to form the nanotube's planar structure, while at the same time the hydrogen radicals are eating the carbon tube away. This was never realized before in nanotube synthesis."

Adding oxygen remedies the problem. By scavenging up the hydrogen radicals—creating a carbon-rich and hydrogen-deficient environment—growth is jumpstarted, spawning a vertical forest of nanotubes.

Using this method, Dai and his colleagues were able to create 4-inch wafers blanketed with SWNTs. In addition, they devised a method for lifting the nanotubes off their original growth substrate and transferring them onto a variety of more desirable mediums such as plastics and metals—materials incompatible with the high temperatures required for nanotube growth. These planted plastics and metals further expand the nanotubes' commercial utility.

Testing already has begun to determine the effectiveness of single-walled carbon nanotube wafers as a thermal interface material, conducting and dissipating heat away from computer chips. The researchers are pursuing additional applications as well.

Postdoctoral fellow Guangyu Zhang is lead author of the study. Other co-authors are chemistry graduate students David Mann, Li Zhang, Ali Javey, Yiming Li and Erhan Yenilmez, research associate Qian Wang and staff scientist James McVittie. James Gibbons, former dean of the School of Engineering, and Yoshio Nishi, director of the Stanford Nanofabrication Facility, both professors of electrical engineering, also contributed to the work.

The study was supported in part by the Global Climate and Energy Project at Stanford. The synthesized nanotubes may be used for hydrogen storage.

Source: Stanford University (by Anne Strehlow)

"Nanobombs" could blow up cancer

Carbon Nanotube

Researchers have created "nanobombs" that can produce nanoscale explosions to blow up cancer. Balaji Panchapakesan of the University of Delaware has reported on the nanobombs in both NanoBiotechnology and Oncology Issues. Panchapakesan says the nanobombs are in the early stages of development, but that the goal is to use them in medical applications. "Make no mistake, we are focused on eradicating cancer," he says.

According to a news release, the nanobombs grew out of work over the past two years with carbon nanotubes:

Originally, he said, the research team was looking at the use of the carbon nanotubes as drug delivery vehicles. Because they are smaller than the size of a single cell, the nanotubes can provide for the highly selective injection of drugs into individual cells.
As they undertook various experiments, however, the team made a startling discovery. "When you put the atoms in different shapes and forms, they take on different properties at the nanoscale," Panchapakesan said. "We were experimenting with the molecules and considering optical and thermal properties, and found we could trigger microscopic explosions of nanotubes in wide variety of conditions."

Explosions in air of loosely packed nanotubes have been seen before in an oxygen environment, creating ignition. However, the work reported by Panchapakesan uses the localized thermal energy imbalance to set off explosions that are intrinsic in nature.

Panchapakesan said the nanobombs are just that, tiny bombs on the nanoscale. "They work almost like cluster bombs," he said. "Once they are exposed to light and the resulting heat, they start exploding one after another."

The bombs are created through the bundling of carbon nanotubes. Nanotubes dissipate heat generated by the light into surrounding air. In bundles, they can't dissipate the heat as quickly and the result is "an explosion on the nanoscale," says Panchapakesan.


According to the news release, this could be exploited to destroy tumors:


When the UD researchers saw the explosions, they realized it might be possible to use the microscopic bombs to kill cancer cells. They recreated the explosions in solutions including water, phosphate and salt, which meant the nanobombs could be used in the human body. In fact the explosions were more dramatic in saline solutions, Panchapakesan said.

"The nanobomb is very selective, very localized and minimally invasive," Panchapakesan said. "It might cause what I would call nanopain, like a pin prick."

He believes the nanobomb holds great promise as a therapeutic agent for killing cancer cells, with particular emphasis on breast cancer cells, because its shockwave kills the cancerous cells as well as the biological pathways that carry instructions to generate additional cancerous cells and the small veins that nourish the diseased cells. Also, it can be spread over a wide area to create structural damage to the cancer cells that are close by.

The nanobombs could also offer advantages over other nanotech treatments as they are destroyed along with cancer cells. Macrophages then clear cell debris and exploded nanotubes, preventing nanoparticles from jamming up in the body.

source: betterhumans

Focus is on adult stem cells

The origin, isolation, & specialization of stem cells

Let others wrestle with the ethics of destroying tiny human embryos to collect the powerful stem cells inside. Dr. Charles Vacanti of Brigham and Women's Hospital is quietly making enormous progress in coaxing the same life-saving potential out of stem cells that have been harmlessly taken from adults. Already, researchers in Vacanti's lab are using adult stem cells to successfully grow new spinal tissue in dogs who've been injured in accidents.

''Putting the ethical debate aside, there are many reasons to focus on adult stem cells," said Vacanti, one of four brothers who have become pioneers in the field of tissue engineering. Unlike embryonic stem cells, he explained, adult stem cells can be taken from the patient himself, so there is no fear that his body will reject the new tissues. Vacanti added that tissue grown from adult stem cells may prove safer in the long run because it is more predictable and less likely to turn cancerous.

Vacanti, an inventor with more than 20 patents to his name, started working with adult stem cells about five years ago when he was looking for a more efficient way to grow human tissues for the treatment of disease and injury.

Despite the buzz at the time over embryonic stem cells, which can turn into any type of cell in the body, Vacanti settled on adult stem cells as a less controversial -- though somewhat less powerful -- alternative.

So far, Vacanti's choice has paid enormous dividends: In the lab, he has grown pancreatic cells that could be vital to treating diabetes. Among the small number of dogs with spinal injuries that he has treated, he said, ''we've had some very significant return of function."

And true to Vacanti's commitment to stay out of the ethical fights that have hampered other researchers, he stresses that all of the dogs treated in his lab were injured by accident and not for research purposes. ''We're not creating any traumas," he said.

source: By Scott Allen, Globe Staff

Group traces genealogy via DNA

SALT LAKE CITY | October 01, 2005 12:27:41 AM IST

DNA Samples

A Salt Lake City nonprofit organization is building a database of family trees using DNA samples to show worldwide biological connections. The Sorenson Molecular Genealogy Foundation has collected 13,489 genetic profiles linked to 550,000 ancestors, Newsweek reported. People must pay about $125 to have a DNA sample -- from a cheek swab -- analyzed by a private laboratory.

The organization's Web site, smgf.org, offers free access to the genetic profiles, but only for information of about long-deceased forebears. Information on people born after 1900 is not made available.

James Sorenson, who provided most of the financial backing for the organization, is a Mormon, whose church emphasizes genealogical research.

source: (UPI)