Imagine carpets that could count people walking on them. Or a T-shirt that can alert medics when a soldier has been wounded. Katherine Bourzac reports in New Scientist that transistors made from polymer-coated cotton may soon make these ideas for wearable electronics into reality.
Previous attempts have not been appealing. Shirts on the market that integrate heart-rate monitors require wiring and bulky electronics boxes. Bourzac writes that “metal and silicon — materials typically used to build electronics — are difficult to weave into fabric.” She adds that although conductive polymer fibers can be woven into garment fabric, people don’t find them comfortable.
Annalisa Bonfiglio at the University of Cagliari in Italy and her colleagues figured out how to coat the cotton with gold nanoparticles and a conductive polymer, which yielded fibers with a desirable texture and feel.
To make a full transistor, Bourzac explains:
The researchers coated the conductive cotton with a semiconducting polymer, which carries current between two electrodes — spots of conductive silver paint at either end of the cotton strand. Varying the voltage in the gate as current flows in the circuit makes the transistor switch between being very conductive and resisting current.
The transistors, which look and handle like cotton thread, can be electrically connected to one another, and to other cotton components, simply by knotting them.
The downside to cotton transistors is that they won’t likely be as fast as silicon transistors in typical microprocessors, Bourzac writes, but they could perform simple computational tasks, such as rigging a carpet to count the number of people walking on it.
“This study opens an avenue for real integration between organic electronics and traditional textile technology and materials,” wrote the researchers in a related journal article.
One example would be biosensors in shirts that can sense wounds. Bourzac describes separate work by Nicholas Kotov at the University of Michigan, Ann Arbor. He created a coating of nanotubes and antibodies that change conductivity around blood. Kotov told New Scientist that the cotton transistors would make biosensors more sensitive because they can amplify signals.
Source: “Cotton transistors weave comfort into electronics,” New Scientist, 11/9/11
Source: “Organic electronics on natural cotton fibres,” Organic Electronics, 9/13/11
Image by sunshinecity, used under its Creative Commons license.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.