Tiny tubes could ease eavesdropping.

Imagine tiny ears listening for whispers of microscopic life on Mars or rustlings of cells within the body.

To create microphones more sensitive than any available today, a team of researchers is developing devices that resemble the microscopic, supersensitive hairs, or stereocilia, of the inner ear. The devices rely on structures that are even more responsive than stereocilia, which bend a few nanometers at the sound of rustling leaves, says Flavio Noca of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Noca and his colleagues are working with arrays of carbon nanotubes--hollow tubes of carbon, each one only several atom-widths in diameter. Noca described the research Dec. 5 at the joint meeting of the Acoustical Society of America and NOISE-CON 2000 in Newport Beach, Calif.

The team collaborated with Jimmy Xu of Brown University in Providence, R.I., to make highly ordered arrays that respond to sound. Xu is part of a group that in 1999 at the University of Toronto first created these arrays. An acoustic sensor wasn't the aim of that work, says Xu.

Nanoscale acoustic sensors might one day journey to Mars or Jupiter's moon Europa, suggests Noca. Or they may take a voyage through the body, looking for activity of cancer cells. The research could also improve hearing aids and reveal more about stereocilia, he adds.

"This proposal of Noca and colleagues is exciting," comments Ray H. Baughman of Honeywell International in Morristown, N.J. "The challenge for realizing their dream of nanoscale ears will be in demonstrating effective mechanisms for converting the minute vibrations of carbon nanotubes to electrical signals, as well as in electrically wiring perhaps billions of nanotubes that are 10,000 times smaller in diameter than a human hair," he says.