Making sense of scent sensors

Stay with me on this one: You don't have a spectrum analyzer in your nose—or do you? Dr. Luca Turin thinks you do, and he's out to turn conventional scientific wisdom on its nose—er, ear.

Of our five senses, smell gets limited use as an electronic troubleshooting tool. While sniffing a fried resistor or a charred transformer can alert us to a problem, we rely mostly on sight and hearing as debugging aids.

But how does our sense of smell function? According to the widely accepted "Shape" theory of olfaction, our sense of smell resembles a truly extensive connector catalog.

Over millions of years our noses have evolved arrays of molecular pattern-recognition cells. When a smelly molecule "plugs into" a receptor, the receptor's nerves send a signal that the brain interprets as a particular smell.

But suppose you encounter a synthesized chemical (e.g., carbon tetrachloride). You note its uniquely pungent odor (not recommended, as carbon tet is toxic), but what equipped you with a pattern-matching sensor for a substance that doesn't exist in the natural world?

Dr. Turin's "Vibration" theory argues that olfactory cells analyze molecular-vibration spectra through electron tunneling, much as an infrared spectrometer examines scattered or transmitted wavelengths (see "What they're doing," at right). His research has yielded an organic diode based on albumin (egg white), which may offer insight into the process.

Here's where the not-invented-here factor kicks in: According to author Chandler Burr, leading olfactory-research authorities refuse to even consider that Turin may be onto something new. Conventional wisdom has a history of making mistakes. Radio frequencies above 3 MHz were once considered useless. Market estimates for mainframe computers topped out at six or seven machines, and the CEO of a minicomputer company publicly stated that he couldn't imagine why anyone would want their own personal computer.

But if Turin's controversial "Vibration" theory of smell is correct, the experts and proponents of olfactory "Shape" theory have followed a false scent and are barking up the wrong tree.

Brad Thompson, Contributing Technical Editor, brad@tmworld.com