A sniff of your breath can reveal that you鈥檙e in for a bout of flu, up to a week before the symptoms appear.
Defence researchers discovered the technique by accident when they were looking for a way to tell whether someone has been exposed to a biological weapons agent.
Our breath contains about 16 per cent oxygen, 78 per cent nitrogen and four per cent carbon dioxide. It also contains traces of other gases, including five parts per billion of nitric oxide.
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NO is an important signalling molecule in the immune system, so Robert Lad at the University of Maine wondered if levels of the gas change when people contract an infection.
In preliminary tests, Lad鈥檚 collaborator Richard Riker of Maine Medical Center found NO levels of around 50 parts per billion in hospital patients suffering from a wide variety of infections, and also in schoolchildren who fell ill a few days afterwards.
With funding from the Defense Advanced Research Projects Agency, Lad鈥檚 team has developed a hand-held NO sensor that is sensitive enough to detect the gas at these levels.
The breath from people being tested passes through a 鈥渕olecular sieve鈥� that isolates NO, which is then oxidised to nitrogen dioxide (NO2). The gas is detected by a semiconductor sensor whose electrical resistance changes in response to its concentration.
The team hopes the breathalyser will help doctors decide if people are going to be well enough over the following few days to work or to have a vaccination. They have also noticed that levels of NO are higher in people with asthma, especially when their asthma is worse.
鈥淲e鈥檒l look at monitoring patients on therapy,鈥� says Jean Cooper of the Clinical Chemistry and Devices section at the US Food and Drug Administration.