Detecting danger

ASEE Prism, May/Jun 2003

Tiny antennas of silver may prove to be extremely powerful tools for detecting chemical and biological agents. Research at Purdue University directed by electrical engineering professor Vladimir Shalaev is demonstrating that arrays of these microscopic antennas are much more sensitive than detectors now in use.

Each antenna is a mere 10 nanometers wide, a fraction of the width of a human hair, and is composed of links of silver particles. Arranged in self-repeating patterns, or fractals, the nanoantennas can be tuned to respond to thousands of different molecules. The signal each antenna receives is amplified by as much as 100,000 times by plasmons, masses of electrons that cover the surface of the nanoantennas. And these enhanced signals are transmitted to a receiver. In the lab, a thin, metal film is coated with the nanoantennas and pressed between glass substrates. Shalaev says he and his team are not yet at the stage of designing practical sensors, but he says that strips of the film could be submerged into water to check for toxic agents in water supplies or placed on walls to detect agents in the atmosphere. "We are still trying to understand the fundamental science," Shalaev says, "but we are close to the time for thinking of practical applications."