Electronic Nose Sniffs out Toxins

Color changes in the new sensor warn of poison gases such as (left to right, top to bottom) chlorine, fluorine, hydrofluoric acid, hydrogen cyanide, B2H2, hydrazine, cobalt chloride, H2S, phosphine, ammonia, NO2 and sulphur dioxide. K. Suslick

While physicists have radiation badges to protect them in the workplace, chemists and workers who handle chemicals don't have equivalent devices to monitor their exposure to potentially toxic chemicals. Researchers have now moved one step closer to developing a small, wearable sensor that can sniff out poisonous gases and toxins.

Designing a simple, fast, inexpensive sensor to detect a range of toxic industrial chemicals is a challenge. Arrays of chemical reactions specific for particular toxins are cumbersome and inflexible. Past attempts to create sensors for detecting diverse industrial chemicals have been problematic because they've relied on weak and highly non-specific chemical interactions.

A research team led by Dr. Kenneth S. Suslick at the University of Illinois at Urbana-Champaign, supported by NIH's Genes, Environment and Health Initiative and the National Institute of Environmental Health Sciences (NIEHS), took a novel approach. The scientists assembled an array of compounds that change color in response to diverse chemical reactions. The overall pattern of color changes, they reasoned, could create unique molecular fingerprints for a range of toxic industrial chemicals.

In the advanced online edition of Nature Chemistry on September 13, 2009, the scientists described a disposable 36-dye sensor they developed. They refer to it as an optoelectronic nose. To test the device, the researchers chose 19 representative examples of toxic industrial chemicals—such as ammonia, chlorine, nitric acid and sulfur dioxide—at concentrations known to be immediately dangerous to life or health. The arrays were exposed to the chemicals for 2 minutes. Most of the chemicals were identified from the array's color changes in seconds. Almost 90% of them were detected within 2 minutes.

"The pattern of the color change is a unique molecular fingerprint for any toxic gas and also tells us its concentration," Suslick says. "By comparing that pattern to a library of color fingerprints, we can identify and quantify the toxic industrial chemicals in a matter of seconds."

The laboratory used inexpensive flatbed scanners for scanning the sensors. The researchers have now developed a fully functional prototype handheld device, similar to a card scanning device, that uses inexpensive white LED illumination and an ordinary camera. They say it will make the process of scanning faster, more portable and even less expensive.

"One of the nice things about this technology is that it uses components that are readily available and relatively inexpensive," says Dr. David Balshaw, a program administrator at NIEHS. "Given the broad range of chemicals that can be detected and the high sensitivity of the array to those compounds, it appears that this device will be particularly useful in occupational settings."

"This paper brings us one step closer to having a small wearable sensor that can detect multiple airborne toxins," says NIEHS Director Dr. Linda Birnbaum. The investigators hope to be able to market a wearable sensor within a few years.