By Rebecca Morelle
Science reporter, BBC News
A device which may pave the way for robotic hands that can replicate the human sense of touch has been unveiled.
Particles in the device emit light to show changes in texture
US scientists have created a sensor that can "feel" the texture of objects to the same degree of sensitivity as a human fingertip.
The team says the tactile sensor could, in the future, aid minimally invasive surgical techniques by giving surgeons a "touch-sensation".
The research is reported in the journal Science.
"If you look at the current status of these tactile sensors, the frustration has been that the resolution of all these devices is in the range of millimetres," explained Professor Ravi Saraf, an engineer from the University of Nebraska in Lincoln, US, and a co-author of the paper.
"Whereas the resolution of a human fingertip is about 40 microns, about half the diameter of a human hair, and this has affected the performance of these devices."
But Professor Saraf and colleague Dr Vivek Maheshwari, also from the University of Nebraska, were able to attain this high level of sensitivity by creating a very thin film made up of layers of metal and semiconducting nanoparticles flanked at the top and bottom by electrodes.
When the film touches a surface any pressure or stress squeezes the layers of particles together. This causes the current in the film to change and light is emitted from the particles, an effect known as "electroluminescence". The visible light is then detected by a camera.
The device image (right) clearly shows the number 5 on this coin
"The beautiful thing is that we have managed to make the device in such a way that the amount of current change, or light, that you get out is exactly proportional to the stress that you apply," added Professor Saraf.
To demonstrate the high sensitivity of the device, the scientists pressed a US one cent coin against it. The sensor revealed the wrinkles in President Lincoln's clothing and the letters TY in liberty.
Professor Saraf said the film, as well as matching the sensitivity of a human fingertip, was also flexible and robust enough to be used repeatedly.
He also said the device could have medical applications.
"The hope is that if you have the resolution close to a human finger in applications like minimal invasive surgery, where the surgeon could actually "touch" while he or she doing the procedure and tell if the tissue is cancerous or abnormal etc, that would increase the success of these surgeries."
Dr Richard Crowder, a robotics expert from Southampton University, commented in an accompanying article in the journal: "The development of tactile sensors is one of the key technical challenges in advanced robotics and minimal access surgery.
"The unique sensor developed by Maheshwari and Saraf could prove to be a key advance in technology, for reasons including relatively simple construction, apparent robustness, and high resolution."
Professor Saraf added that now he would like to see if he could create a device that can detect temperature changes as well as texture, enabling it to closer mimic the sensations humans can feel.