Advanced ‘artificial skin’ senses touch, humidity, and temperature
July 10, 2013
Technion-Israel Institute of Technology scientists have discovered how to make a new kind of flexible sensor that one day could be integrated into “electronic skin” (e-skin) — a covering for prosthetic limbs that would allow patients to feel touch, humidity, and temperature.
Current kinds of e-skin detect only touch, but the Technion team’s invention “can simultaneously sense touch (pressure), humidity, and temperature, as real skin can do,” says research team leader Professor Hossam Haick.
Additionally, the new system “is at least 10 times more sensitive in touch than the currently existing touch-based e-skin systems.”
Researchers have long been interested in flexible sensors, but have had trouble adapting them for real-world use Haick says. A flexible sensor would have to run on low voltage (so it would be compatible with the batteries in today’s 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. These sensors would also have to be able to be manufactured quickly, easily, and cheaply.
The Technion team’s sensor has all of these qualities, Haick says. The secret: monolayer-capped gold nanoparticles that are only 5–8 nanometers in diameter, surrounded by connector molecules called ligands.
“Monolayer-capped nanoparticles can be thought of as flowers, where the center of the flower is the gold or metal nanoparticle and the petals are the monolayer of organic ligands that generally protect it,” says Haick.
The team discovered that when these nanoparticles are laid on top of a substrate — in this case, made of PET (flexible polyethylene terephthalate), the same plastic found in soda bottles — 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 how thick the substrate is, as well as what it is made of, scientists can modify how sensitive the sensor is. Because these sensors can be customized, they could in the future perform a variety of other tasks, including monitoring strain on bridges and detecting cracks in engines.
“The sensor is very stable and can be attached to any surface shape while keeping the function stable,” says Dr. Nir Peled, Head of the Thoracic Cancer Research and Detection Center at Israel’s Sheba Medical Center, who was not involved in the research.