Originally Published MPMN September 2009

BREAKTHROUGHS

Manufacturing Advance Purifies Carbon Nanotubes

Stephanie Steward

Experts anticipate that carbon nanotubes (CNTs) will play a major role in a host of next-generation medical device technologies, including a variety of sensors for drug-delivery, in vivo, and other applications. But despite the possibilities that CNTs present, they also have a major drawback: They are typically made using techniques that can result in the formation of electrochemically active metal impurities, such as iron and cobalt, that can compromise end products.

Sustainable Carbon NanoTechnology and Engineering Ltd. (SCNTE) is devoted to ridding CNTs of metal impurities. To that end, the company has developed a proprietary solid-state carbothermal conversion process for fabricating CNTs that does not use metal catalysts. SCNTE’s material is also more consistent than standard CNTs, which aids in the development of reliable sensor platforms, the company says.
“Carbon nanotubes are always contaminated with transition metal catalyst particles,” explains Bill L. Riehl, SCNTE COO. Such particles are a by-product of such manufacturing techniques as arc discharge, laser ablation, and chemical vapor deposition. Without undergoing extensive postfabrication purification, CNTs with these impurities pose problems for medical devices. “These particles are, at the minimum, inconvenient for analytical and medical or biomedical use,” Riehl notes. “More typically, their presence severely restricts the use of the material for medical applications due to large quantities of iron left from production.”
Because of the presence of metal catalysts, conventional CNTs cannot be used in such sensor applications as drug-delivery devices without major advances in device technology, Riehl remarks. “Residual metal catalysts interfere with sensor signals and often lead to false positives or negatives due to their residual chemical and electrochemical activity.”
But in their purified state, CNTs can play an important role in future sensor applications. The electronic properties of CNT-based materials promote the electron-transfer reaction of many biologically significant species. This capability, in turn, aids in the detection of these substances.
Based on its high-purity carbon nanotube material, SCNTE is developing an implantable glucose oxidase biofuel cell to power in vivo sensors. The material may also find its way into CNT-array sensors for detecting homocysteine, elevated levels of which serve as a marker for cardiovascular diseases and diabetes. Incorporated into paste electrodes, CNTs enhance the voltammetric sensing of homocysteine, which holds promise for future glucose testing. Riehl concludes, “The detection of homocysteine will be the new glucose test.”

Sustainable Carbon NanoTechnology and Engineering Ltd.
Kettering, OH
www.scnte.com
Copyright ©2009 Medical Product Manufacturing News