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Intelligent Machines

Carbon-Nanotube Thread

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

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.

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.

“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.

The work “will open an avenue to a new generation of wearable materials,” predicts Hinestrosa. He says that Kotov’s nanotube-coated cotton “keeps the properties of the textile and adds new functions.” Albumin-sensing clothing for soldiers could alert remote medical teams to the fact that a soldier is bleeding, says Kotov. The change in current indicating the presence of a wound could be picked up by a wearable computer that would then send out a message. Textiles incorporating antibody-treated nanotubes could also alert the wearer to allergens by illuminating LEDs or sending a message to a cell phone. Clothing incorporating multiple strips of sensing fabric, each targeted to a different biomarker or to parameters like temperature, would be capable of more-sophisticated monitoring of vital signs.

“We’re getting closer to the goal of intelligent textiles,” says Pulickel Ajayan, a professor of mechanical engineering and materials science at Rice University. Kotov’s work, he says, is a good demonstration that textiles incorporating nanomaterials can do more than just conduct electricity.

The advantage of incorporating carbon nanotubes into textiles, says Hinestrosa, is that they can perform many different functions, making it unnecessary to add on extra, bulky components. “You can use the same threads as conductors, sensors, and as transducers of the signal,” he says. For example, in clothes that adjust to the weather, carbon nanotubes could sense the temperature, carry the reading to a wearable computer, then carry a signal from the computer that directs the fibers to conform to a more open weave if it’s hot out.

Kotov notes that his textiles’ biosensing mechanism, which relies on changes in current, is uncomplicated. In the simplest possible scenario, the change in current indicating the presence of a protein of interest can be read using nothing more than a battery and a lightbulb. “Despite the simplicity of the concept, the sensitivity is amazing,” Kotov says. By contrast, conventional methods for identifying proteins require multiple preparation steps in a wet lab and fluorescence imaging equipment.

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