Today's electronic noses are not up to the job, he says. Although e-noses have been around for a while – and are used to sniff out rotten food in production lines – they lack accuracy.
That's because e-noses use quartz rods designed to vibrate at a different frequency when they bind to a target substance. But this is not a foolproof system, as subtly different substances with similar molecular weights may bind to the rod, producing a false positive.
Instead, Takeuchi believes there is nothing quite as good as biology for distinguishing between different biomolecules, such as disease markers in our breath. So he and his team have developed a living smell sensor.
First, immature eggs, or oocytes, from the African clawed frog Xenopus laevis were genetically modified to express the proteins known to act as smell receptors. He chose X. laevis cells as they are widely studied and their protein expression mechanism is well understood.
The team then placed the modified cells between electrodes and measured the telltale currents generated when different molecules bound to the receptors. They found this method can distinguish between many nearly identical biomolecules.
As a proof of concept, Takeuchi has built a robot that shakes its head when moth pheromones are sensed by the nose.
He now wants to extend the frog-based technology. "The X. laevis oocyte has high versatility for the development of chemical sensors for various odorants," he says. "We believe that a shared ability to smell might open a new relationship between man and robot."
Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1004334107.
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