Thursday, November 6, 2003
Quantum dots, nanowires and other nanoscale structures populate the frontier of semiconductor research, collectively aimed at downsizing chip components to the molecular scale. So far piezoelectric materials have been used to fabricate nanowires and nanobelts (ring-shaped nanowires) for experimental nanoscale lasers, field-effect transistors, gas sensors, cantilevers and resonators.
But none of these have been "single crystal" and therefore only partially exploit the piezoelectric phenomenon, according to one research scientist, who now claims to have fabricated the world's first single-crystal nanosprings that not only outperform predecessors but also promise to enable single-molecule sensors.
"We have fabricated nanosprings for the first time in single-crystal zinc oxide," said Zhong Lin Wang, director of Georgia Tech's Center for Nanoscience and Nanotechnology and a professor in the School of Materials Science and Engineering. "Quantum dots and quantum wires [nanowires] are mostly semiconductors today, but ours [are] so far the only [single-crystal] piezoelectric nanowires." He performed the work with a fellow research scientist at Georgia Tech, Xiang Yang Kong.
Because piezoelectric semiconductors are natural resonators, they don't need all the support circuitry that normal semiconductors need to make them process and emit signals. When stimulated physically, a piezoelectric material will naturally oscillate at a known frequency. Therefore, if its surface is treated to attract, for example, a protein from a cancer cell, Wang said, then even a single molecule of that protein could be detected with one of his nanosprings.
"We just developed our first application, called the positive resonance technique for detecting biomolecules with nanosprings," Wang said. "If you have a single molecule on the surface [of a nanospring], you can detect a change in its resonant frequency, and by determining the frequency, you can tell what molecule you have."
Wang is now working with multidisciplinary specialists to devise a micron-sized "pill" that disperses millions of such nanosprings all through the entire body, and radios through the skin if cancer cells are detected.
"We want to detect cancer cells," said Wang. "We see the potential for individual, real-time, early detection of cancer, where we transmit a signal wirelessly for about 24 hours. As the nanosprings work their way through your body, they detect any cancer there and send a radio frequency signal out [through the skin]," said Wang.
Wang promises a prototype of his micron-sized "pill" by year's end. Besides biomedical applications, Wang also claims that his nanosprings are compatible with traditional photolithographic techniques of chip-making and that, for traditional sensors and actuators, they can be grown on-chip wherever they are needed as highly sensitive transducers.
By: DocMemory
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