Plastic nanowires sense gasses

Cornell University researchers have devised a simple way to position conducting polymer nanowires on an electrode, and have made a prototype high-speed chemical detector that is capable of sensing minuscule amounts of ammonia gas.

The researchers are working on other polymer materials that are able to detect other gasses. The method could ultimately be used to make a device that has an array of wires sensitive to different chemicals. Such a device would be able to rapidly detect and analyze the composition of gasses in the air, according to the researchers.

Key to the method was finding a way to precisely orient individual nanowires parallel to the electrodes. The researchers' scan-tip electrode spinning deposition method involves electrostatically moving a droplet of solution from an arrow-shaped microscopic tip to the surface. The polymer solution dries in transit to the substrate, producing nanowires oriented in one direction. The researchers completed the device by positioning patterned gold electrodes on the substrate perpendicular to the nanowires.

The nanowires had diameters of 100 to 500 nanometers. As the nanowires absorbed ammonia, their electrical conductance decreased. The response times of the nanowires corresponded to the differences in diameter and the resulting diffusion time of ammonia gas into the wires. The researchers' prototype quickly detected ammonia gas at concentrations as low as 500 parts per billion.

The method makes it easy to integrate nanowires with conventional electronics, according to the researchers.

Polymer nanowire sensor devices could be practical in three or four years, according to the researchers. The work appeared in the February 27, 2004 issue of Nano Letters.