What do you get if you cross a rat, a jellyfish and brewer鈥檚 yeast? Happily, the answer is not the latest genetically modified food, but a low-cost explosives detector.
Danny Dhanasekaran, a molecular biologist at Temple University in Philadelphia, Pennsylvania, has coaxed a simple yeast into harnessing a rat鈥檚 sense of smell to sniff the explosive trinitrotoluene (TNT), a primary ingredient in many explosive devices. When it finds it, the yeast emits a warning using the jellyfish鈥檚 ability to softly glow.
Funded by the Pentagon鈥檚 Defence Advanced Research Projects Agency, Dhanasekaran hopes to create a lightweight detector that is much cheaper than today鈥檚 precision-engineered electronic noses. The yeast sensor could one day be installed at ports and railway stations, or built into a PDA-size device, to warn of the presence of explosives, or chemical or biological weapons.
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Dhanasekaran鈥檚 team first cloned the genes for smell receptor proteins in rats. There are around 500 such proteins, and different odour molecules latch onto each one, producing enzymes that activate electrical signal pathways to the brain. Brewer鈥檚 yeast, Saccharomyces cerevisiae, uses the same type of protein receptors and signalling to detect pheromones during reproduction, so the researchers decided to use the yeast as their communications channel, and shuttled the cloned rat genes into its genome. 鈥淵east can be tricked into using the rat olfactory signals very easily,鈥� says Dhanasekaran.
Then, to alert users that the yeast has detected an explosive substance, they inserted a jellyfish gene for a green fluorescent protein, visible under ultraviolet light, which is produced when the olfactory pathway is activated (Nature Chemical Biology, DOI: 10.1038/nchembio882).
Once they had built the detector, five of the 500 rat genes were inserted in any one yeast, and each yeast was then exposed to a molecule similar to TNT. In this way the team was able to isolate a receptor called Olfr226 that best detects the molecule. They now hope to identify receptors for other target molecules.
If they succeed, Dhanasekaran envisages the yeast, which can live up to 15 days in the form of a semi-solid film, one day being supplied in cartridges that slot into a PDA-sized sensor.
