New method to develop 'artificial skin' with sense of touch

E-skin! Researchers have discovered a new and cheaper method to develop 'artificial skin' which can sense touch, humidity and temperature just like the real skin.
Using tiny gold particles and a kind of resin, a team of scientists at the Technion-Israel Institute of Technology in Haifa, Israel has found how to make a new kind of flexible sensor that could be integrated into electronic skin, or e-skin.
The new system is at least 10 times more sensitive in touch than the currently existing touch-based e-skin systems, researchers said.
If scientists learn how to attach e-skin to prosthetic limbs, people with amputations might once again be able to feel changes in their environments, they said.

The secret lies in the sensor's ability to detect three kinds of data simultaneously. While current kinds of e-skin detect only touch, the new invention "can simultaneously sense touch, humidity, and temperature, as real skin can do," said 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," said Haick.

Researchers have long been interested in flexible sensors, but have had trouble adapting them for real-world use.
To make its way into mainstream society, 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.

In addition, these sensors would also have to be able to be made quickly, easily, and cheaply, researchers said.
The Technion team's sensor has all of these qualities. The secret is the use of monolayer-capped nanoparticles that are only 5-8 nanometers in diameter, made of gold and 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," said 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 resulting compound conducted electricity differently depending on how the substrate was bent.

This electrical property means that the sensor can detect a large range of pressures, from tens of milligrammes to tens of grammes.
And by varying how thick the substrate is, as well as what it is made of, scientists can modify how sensitive the sensor is.
The findings appear in the journal ACS Applied Materials & Interfaces.