Uncommon Sense

In an old fable, a man stands outside a bakery for a while savoring the smells of bread and pastries emerging from the shop. Eventually, the baker comes out, angry that the man has been enjoying the aromas of his products for free, and demands payment. The man on the street refuses. A wise man approaches, and the two ask for his help resolving the dispute. The sage asks the man who has been smelling the bread to show him some coins. The sage looks them over, jostling and clinking them together in his hand. He then lets them fall to the sidewalk, picks them them up, and taps them several times against the bakery window before handing them back to the man. Turning to the baker, he says, "This man has paid you for the smell of your bread with the sound of his money."

Laura Bush

The concept of the "optical nose", also takes an approach to problem-solving that involves an unexpected application of the senses. When developing a spectroscopic technique, most people would not consider the sense of smell. Yet some wise scientists have done just that, and have studied the way trained sniffer dogs detect explosives. Dogs' effectiveness in detecting explosives is surprising, because many explosive compounds have very low vapor pressures at ambient temperature. For example, the expected vapor concentration of TNT from a landmine is orders of magnitude lower than a trained dog's limit of detection. So how can a dog detect it? The answer, researchers have found, is that sniffer dogs don't smell only the explosives, but a combination of scents from degradation by-products as well as solvents and synthetics used in making the explosive device; this combination of odors is known as the explosivebouquet. By studying the components of the bouquet, instrument developers can identify the compounds that their spectroscopic instruments for explosive detection should target.

Of course, unlike the problem in the fable, the challenge of detecting explosives is quite complex, so a creative use of the senses did not result in a quick fix. For the optical nose approach to work, a set of high-resolution spectral signatures must be available for the volatile organic compounds (VOCs) involved. Therefore, creating a database of spectra for the highest priority explosive-related VOCs — including rotationally resolved spectra — is the next step in the process. That work is now under way.

The optical nose approach does, however, offer a good example of creative problem-solving. Instead of applying common sense, these researchers applied other senses, and doing so has opened up an avenue to tackling a spectroscopic challenge.

Laura Bush is the editorial director of LCGC North America and Spectroscopy, lbush@advanstar.com.