Deadly gas leaks are an everyday hazard of modern life.
Unfortunately, conventional gas alarms often fail to detect the presence of toxic fumes until it’s too late.
But a team of Stanford scientists has developed a gas detector that is a thousand times more sensitive than any commercially available device operating at room temperature.
Hongjie Dai, assistant professor of chemistry, and Kyeongjae (KJ) Cho, assistant professor of mechanical engineering, described their findings in the January 28 issue of the journal Science.
The experimental sensor, built in Dai’s chemistry lab, uses carbon nanotubes only one nanometer thick. A nanometer is one-billionth of a meter — about 50,000 times smaller than the width of a human hair.
Researchers placed two miniature metal pads at opposite ends of a nanotube, creating a semiconductor capable of detecting tiny changes in an electrical current when only a handful of gas molecules are present.
This carbon nanotube (in blue), just one nanometer in diameter, has molecules of poisonous nitrogen dioxide gas (in violet, at bottom) bonded at the bottom. Nanosensors can detect poisonous gas at room temperature even if only a few gas molecules are present in the atmosphere. A nanometer is about 50,000 times smaller than the width of a human hair.
Scientists tested the device using two common forms of noxious gas: ammonia and nitrogen dioxide.
Ammonia (NH3), a well-known ingredient in household cleaners, is widely used in the manufacture of fertilizers and plastics. Inhaling too much ammonia gas can be fatal. Nitrogen dioxide (NO2) is a by-product of kerosene heaters, car exhaust and tobacco smoke. The Environmental Protection Agency warns that prolonged exposure to NO2 gas may cause lung damage and increase respiratory infections in children.
The experimental nanotube sensor was able to instantly detect ammonia and nitrogen dioxide molecules at levels of just 20 parts per million (20 ppm), making the Stanford device a thousand times more sensitive than conventional gas detectors.
Dai points out that, in addition to its microscopic size, a nanotube sensor also has the advantage of being able to operate at room temperature, unlike commercial gas detectors which have to heat up to 900o F (500C) to function.
‘This is really a new kind of material for sensors,’ says Dai, adding that the nanotube prototype soon may be tested for commercial use. He also notes that his research team is working on a device that will pick up traces of carbon monoxide and other gases.
Cho believes that the sensor will have other applications for detecting biochemical weapons, land mines, air pollution and even organic molecules in space.
Cho and Dai are part of the Stanford Nanotechnology Research Group within the Laboratory for Advanced Materials. The Science article is co-authored by chemistry graduate students Jing Kong and Nathan Franklin; postdoctoral fellow Chongwu Zhou; mechanical engineering graduate student Shu Peng; and materials science and engineering undergraduate student Michael Chapline.
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