June 13, 2006 — A transparent film 1,000 times thinner than a human hair could someday help doctors detect cancer cells and give future robots the sensitivity of human touch.
The film sensor is not only the first to use nano-sized particles that glow when pressed, but can be produced without the costly manufacturing process common for similar materials.
"It is a much cheaper and more practical device for the applications," said Ravi Saraf of the University of Nebraska, Lincoln. Saraf and Vivek Maheshwari recently reported their findings in the journal Science.
Typically, touch sensors are tiny electrical components made by machining microscopic parts. The equipment, skill and clean-room environment necessary to do the job add hefty expense to the bottom line.
Instead of machines, Saraf and Maheshwari used liquid.
In separate solutions, the researchers suspended nano-sized particles of gold, which conduct electricity, and cadmium-sulphide, a semiconductor that glows under an electrical current.
The researchers laid down layers of the solutions onto a glass base, separated by insulating materials. When the liquid dried, it formed a transparent, multilayer structure, which the researchers then sandwiched between electrodes.
When an electrical current was run through the electrodes and pressed down on the material, electrons in the current jumped from one nano-sized particle to the next, "tunneling" through the layers.
Electrons in the cadmium layer released a photon, producing a glow.
The researchers found that the harder they pressed the material, the stronger the current flowed, and the brighter the material glowed.
"The most interesting part is the fabrication process," said Vincent Hayward, professor of electrical and computer engineering working on touch technology at McGill University in Montreal. While the cleverness, he said, lies in "the very small size of the particles to transfer a mechanical event into an optical event."
"This is truly something quite different here," he said.
The difference in brightness was picked up by camera and measured with image processing software to show that the sensitivity of the material fell within range of that of a human finger.
In certain applications, using a camera would not be necessary, said Saraf. A computer could pick up the strength of the electrical current to determine the amount of force being applied to the material.
Saraf thinks the material could eventually be coated onto the end of minimally invasive surgical devices, such as laparoscopes. As the laparoscope probed human tissue, it could send back tactile information to help the doctor navigate.
But first, Saraf is investigating whether the film could be used to test tissue for cancerous cells, which tend to be noticeably harder than healthy ones.
