Chemist Developing Artificial Nose
to Detect Disease, Pollution
February 21, 2000
t will sniff out explosives, smell spoiled meat, and diagnose disease. It will do practically everything, in fact, except sneeze.
It's the artificial nose - not a prosthesis, but a scientific tool, a small hand-held device that can detect and identify thousands of odors. And it will do its work almost instantaneously, says Gregory Sotzing, an assistant professor of chemistry in the Institute of Materials Science.
Sotzing, who came to UConn in September from the California Institute of Technology, specializes in designing new technologies for artificial noses and tongues.
"Smell and taste are difficult senses to study," he says. The human olfactory system is intricate, and, perhaps, the least understood of the senses, he notes. How, for example is the nose able to distinguish between the myriad aromas that bombard our senses every day? How does the nose recognize the bouquet of a fine wine, the scent of an expensive perfume or the stench of rotting fish?
We can smell things because airborne molecules interact with receptors attached to millions of olfactory neurons in the nose. These signals are sent to a region of the brain that processes the information, then sends signals to other parts of the brain, allowing us to sense a particular odor.
The olfactory system does not have a receptor for every odor: the brain identifies a pattern of neurological responses created by a scent, he notes.
For years, human noses have sniffed out everything from rotten food and cosmetics to human armpits in anti-perspirant tests. Now, a machine may do that work.
Sotzing, an organic chemist, started his work on noses while doing postdoctoral research in California. There, he designed and constructed an electronic nose that was intended to detect diseases. "We were trying to 'smell' diseases from people's breath," he says. Collaborating with a clinician in Philadelphia, he studied expired breath from patients with renal failure and fish odor syndrome. Although his data set was not large, the results were promising.
Sotzing came up with an electronic nose "consisting of an array of sensors that would head for the target molecules for these particular diseases," he says.
His nose was based on an array of chemical sensors made of conductive polymer composites. These sensors change resistance when exposed to a vapor. Since each sensor is different, each polymer produces a different change in resistance. These changes create a pattern of responses that can identify a particular scent.
"One has to 'train' the electronic nose much like one trains their own nose to a particular odor," Sotzing explains. "The more the nose smells that odor, the more experienced it becomes."
"The key is to be able to detect and discriminate," Sotzing says. "If you can't tell chemical warfare agents in water from pure water, you're in big trouble. The sensors have to be stable in water, and, furthermore, they can not be sensitive to water. Otherwise, it would be virtually impossible to detect a chemical warfare agent - sort of like trying to find the needle in the haystack," he explains.
When he was doing disease detection at Caltech and working with people's breath, for example, he had to make sure that he overcame the humidity and effects from the thermal fluctuations and condensation of water coming from breath. "You can modify the material of the sensor such that it doesn't like water," he says.
Although a number of companies are developing artificial noses, not all will work well, Sotzing predicts. "It's all in the design of the materials," he says. "In a broad sense, you can say 'artificial olfaction,' but it boils down to what the detectors are made of - the chemical structures of the detectors."
Currently, physicians are using expensive and user-unfriendly instrumentation for breath analysis, Sotzing says: "The idea of the nose is to make a hand-held instrument that is easy to use, inexpensive and highly sensitive."
Sotzing is now designing detectors that will sniff out chemical warfare agents, locate land mines and identify different pollutants in the environment. He is also developing sensors for an artificial tongue that could identify 'tastes' in liquids - such as river water, ocean water, wine and beer, and more importantly blood for disease detection.