Connecting a sensitive detector that can distinguish hundreds of different chemical compounds to a module that mimics the way animals recognize odors is letting researchers at the National Institute of Standards and Technology (NIST) devise a sensitive “electronic nose.” This sniffer is more adept than conventional methods at recognizing airborne molecules even for chemicals it has not been trained to detect. It is also said to be reliable enough to deal with changes in sensor response that come with wear and tear. The detector could help the military and other security agencies detect indicators of disease, nerve agents, and environmental contaminants.

The detector works on interactions between chemical species and semiconducting sensing materials placed on top of a microheater developed at NIST. Eight different sensors in the form of oxide films are deposited on the surfaces of the microheaters. Precise control of the 16 individual heating elements let the scientists treat each element as a collection of sensors at 350 temperature increments from 150 to 500C. So effectively, the sniffer has about 5,600 sensors.

The electronic nose needs training to recognize chemical signatures of different smells before it can deal with unknowns. The advantage of this system, says NIST researchers Barani Raman and Steve Semancik, is that the array need not be exposed to every chemical it could come in contact with to recognize or classify them. Breaking the identification process into discrete steps avoids ‘noisy’ portions of the sensor response, thereby guarding against sensor drift or aging.