The theory that our sense of smell has its basis in quantum physics events is gaining traction, say researchers. The idea remains controversial, but scientists reporting at the American Physical Society meeting in Dallas, US, are slowly unpicking how it could work. The key, they say, is tiny packets of energy, or quanta, lost by electrons. Experiments using tiny wires show that as electrons move on proteins within the nose, odor molecules could absorb these quanta and thereby be detected. If the theory is right, by extending these studies, an "electronic nose" superior to any chemical sensor could be devised.
Lock and key
The means by which a detected molecule is translated into a smell within the brain has already been the subject of Nobel prize-winning research. But how precisely an odorant molecule is detected remains a mystery. As with the picture of molecular interactions that drives our understanding of enzymes and drugs, the very shape of odorant molecules has been assumed to be the way it is detected in the nose. In this scenario, molecules are seen to be the "key" that fits neatly into a detector molecule in the nose that acts as a lock.
But in 1996, Luca Turin, now of the Massachusetts Institute of Technology in the US, suggested that the "vibrational modes" of an odorant were its signature. Molecules can be viewed as a collection of atoms on springs, and energy of just the right frequency - a quantum - can cause the spring to vibrate. Since different assemblages of molecules have different characteristic frequencies, Turin proposed, these vibrations could act as a molecular signature. The idea has been debated in the scientific literature, but presentations at the American Physical Society meeting put the theory on firmer footing.
Most recently, Dr Turin published a paper showing that flies can distinguish between molecules that are chemically similar but in which a heavier version of hydrogen had been substituted. Like a spring with a heavier weight at one end, the vibration frequency is lowered, and flies appear to notice. "There's still lots to understand, but the idea that it cannot possibly be right is no longer tenable really," said Andrew Horsfield of Imperial College London. "The theory has to at least be considered respectable at this point," he told BBC News.
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