Nanotech News

November 14, 2005

New Technique Simplifies Carbon Nanotube Production, Creates Opportunity for Novel Uses

Over the past year, carbon nanotubes have emerged as a promising type of nanoscale material for delivering contrast agents to tumors and drugs and other molecules into malignant cells. Now, researchers at Stanford University have devised a novel method for growing identical carbon nanotubes on a large scale, a feat that had eluded investigators. Moreover, the way in which the carbon nanotubes are produced – in what could be called a carpet of nanotubes – opens up the possibility of creating new filters and through-the-skin drug delivery devices using the nanotubes.

Vertical carbon nanotubes blanket a silicon wafer to form a plush carpet. (Source: Hongjie Dai, Ph.D., Stanford University.)

Writing in the journal Proceedings of the National Academy of Sciences, Hongjie Dai, Ph.D., and his colleagues describe how they modified the industry’s standard approach, known as plasma-enhanced chemical vapor deposition (PECVD), for making carbon-based nanomaterials to achieve ultra-high-yield growth of so-called single-walled carbon nanotubes, or SWCNTs. The key, the researchers found, is to add oxygen to the standard reaction mix for making carbon nanotubes. Adding oxygen has the effect for scavenging random hydrogen atoms that are normally present in the PECVD process and that impede growth of carbon nanotubes.

Using this method, Dr. Dai and his colleagues were able to create 4-inch wafers blanketed with SWCNTs. 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. The ability to plant carpets of nanotubes onto plastics and metals further expand the nanotubes' commercial utility.

One potential use of nanotube-carpeted plastic could be as a device for delivering drugs through the skin – the nanotubes could be loaded with drug. When placed against the skin, the ends of the nanotubes could interact with the outer membranes of skin cells and allow drugs to enter those cells for distribution throughout the body.

Another potential application would be in high-throughput filters that could be used to more readily purify drug molecules during manufacturing or to act as molecular separators for sensitive and specific biosensors. A new paper published in the journal Nature, from a group headed by Bruce Hinds, Ph.D., at the University of Kentucky, describes such a filter made from carbon nanotubes. An abstract of that paper, titled, “Nanoscale hydrodynamics: enhanced flow in carbon nanotubes,” is available through PubMed.
View abstract.

The work of Dr. Dai and his colleagues is detailed in a paper titled, “Ultra-high-yield growth of vertical single-walled carbon nanotubes: Hidden roles of hydrogen and oxygen.” An abstract is available through PubMed.
View abstract.