Cotton transistors weave comfort into electronics

THE next generation of wearable electronics could be a lot more comfortable, thanks to transistors made from cotton fibres. Such transistors may soon make for wearable electronics as comfy as your favourite pair of jeans or T-shirt.

Some electronic textiles, such as shirts that integrate heart-rate monitors, are already on the market. But these products incorporate wires and bulky boxes of electronics, says Annalisa Bonfiglio at the University of Cagliari, Italy, who led the new work in cotton. What's more, metal and silicon - materials typically used to build electronics - are difficult to weave into fabric, while conductive polymer fibres that can be woven do not match the comfort levels most people expect from their garments.

Cotton, by contrast, is perfect to wear but not a good conductor.

Bonfiglio and colleagues have now found a way to make cotton conductive enough to use in transistors, the devices at the heart of most electronics. They did it by giving cotton fibres a coating of gold nanoparticles combined with a conductive polymer. This material forms the gate of the transistor, which regulates the flow of current from one electrode to another.

To make a full transistor, 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 team's work will be published this month in the journal Organic Electronics.

Cotton transistors won't match the speed of silicon transistors in typical microprocessors any time soon, but they could perform simple computational tasks. For example, a carpet could count the number of people in a room or sense the temperature.

The new transistors also promise to make wearable biosensors better. In separate work, Nicholas Kotov at the University of Michigan in Ann Arbor has coated cotton threads in nanotubes and antibodies that change their conductivity in the presence of blood. Such sensors could warn medics if a soldier is wounded. Kotov says cotton transistors would make sensors more sensitive, because they can amplify signals.

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