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A team of scientists at the Technion-Israel Institute of Technology, Haifa, say that using tiny gold particles and resin they have discovered how to make a new kind of flexible sensor that could some day be integrated into electronic skin (e-skin). They say that this e-skin, when attached to prosthetic limbs, could help people with amputations to feel changes in their environments.

The new sensor incorporated in the e-skin can detect three kinds of data—touch, humidity, and temperature—simultaneously as real skin can. And, they say, the new system is at least 10 times more sensitive in touch than current touch-based e-skin system technology.

A flexible sensor needs to run on low voltage to be compatible with batteries in portable devices, measure a wide range of pressures, and make more than one measurement at a time, including humidity, temperature, pressure, and the presence of chemicals. In addition, they need to be able to be made quickly, easily, and cheaply.

The Technion team's sensor uses monolayer-capped nanoparticles only five to eight nanometers in diameter. They are made of gold and surrounded by connector molecules called ligands. The team discovered that when nanoparticles are laid on top of a substrate, such as the plastic PET (polyethylene terephthalate), the resulting compound conducted electricity differently depending on how the substrate was bent. The bending motion brings some particles closer to others, increasing how quickly electrons can pass between them.

This electrical property means that the sensor can detect a large range of pressures, from tens of milligrams to tens of grams. And by varying the substrate’s thickness, and its content, scientists can vary the sensor’s sensitivity. Their findings appear in the June issue of ACS Applied Materials & Interfaces.

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