Wednesday, November 19, 2008

Carbon-Nanotube Thread

Fabrics woven from highly conductive, nanotube-coated cotton are wearable biosensors.

By Katherine Bourzac

Nanotube textiles: Cotton thread dipped in a mixture of carbon nanotubes and conductive polymers carries enough electrical current to light up a light-emitting diode. Credit: Bong Sup Shim

Intelligent textiles could monitor vital signs, warn of allergens, even cool off their wearers when the temperature rises. But wiring up fabrics with sensors has proved a challenge: most electronic textiles are too bulky to be worn comfortably and can't perform sophisticated operations. Now researchers have coated conventional cotton thread with highly conductive, biosensing carbon nanotubes. The threads can be woven into fabrics that are lightweight and wearable but act as simple, sensitive sensors that can, among other functions, detect human blood.

"We wanted to create an alternative to the very complex electronic textiles" developed previously, says Nicholas Kotov, a professor of chemical engineering at the University of Michigan. Many electronic textiles incorporate metallic threads, which are heavy and prone to corrosion, or fiber optics, which are bulky. And while other groups have tried to incorporate carbon nanotubes, which can carry both electrical current and data, into textiles, the researchers have had little success.

Kotov's fabrics, which are made by dipping cotton into a mixture of the carbon nanotubes and a conductive polymer, carry more current than previous nanotube textiles. In work published online in Nano Letters, Kotov showed that a light-emitting diode (LED) put into a circuit between two of the coated cotton threads shines brightly. The demonstration that a textile can carry this much current is "breathtaking," says Juan Hinestrosa, a professor of fiber science and head of the Textiles Nanotechnology Laboratory at Cornell University.

The Michigan group is also the first to demonstrate biosensing with nanotube textiles. Carbon nanotubes are being extensively developed for chemical sensing and clinical diagnostics in part because it's simple to decorate them with binding molecules like antibodies: when a target molecule binds to the nanotube, it changes the nanotube's conductivity in a way that is detectable. In this case, Kotov decorated the carbon nanotubes with antibodies to the human blood protein albumin, demonstrating that the textiles could be used to detect human blood. The textiles don't respond to bovine albumin, showing that the sensors are very specific to their target.