London, May 10 : A team led by an Indian researcher has developed an electronic nose coated with 'mouse urine', which they say, can help sniff out trace quantities of explosives or pollutants, or pick out different smells for food quality control.
Currently, the electric noses in the market use materials that change their physical properties when the target molecule is caught on them. Some polymers, for example, change their conductivity when a small molecule such as ammonia binds to their surface.
But these materials are sometimes not very sensitive, tend to degrade over time, and are generally suitable only for niche applications.
Therefore, Krishna Persaud from the University of Manchester, UK, turned to mouse urine because of the high concentrations of small and hardy Major Urinary Proteins (MUPs) it contains. These proteins can hold scent molecules tightly and release them slowly - a handy trick for mice marking their territory.
Similar proteins are found in mice and other animals' noses to help them detect odours.
The research team recreated mice MUPs and coated them on a quartz-crystal microbalance - a device that has been used in sensors for many years. The crystals used in these devices vibrate at a specific frequency when a current runs through them. If the mass of the crystal changes - by a small molecule landing on it and attaching to the protein coat, for example - so does the vibration frequency, which can be measured.
These devices are sensitive to just a few nanograms and can detect molecules at concentrations of a few parts per million.
To improve sensitivity, you need to be able to bind lots of odour molecules very efficiently - which is just what MUPs can do.
"By putting the [MUPs] on a quartz crystal microbalance we can detect parts per billion of volatile [substances]," Nature quoted Persaud, as saying.
Vincent Rotello, an expert in molecular recognition at the University of Massachusetts in Amherst, says that Persaud's extra-sensitive, protein-based receptor is an important advance, but adds that sensor technology still has a way to go. They still need to be able to differentiate smells better, for instance.
At the moment, the human nose is much better at this than any machine, says Rotello.
"We can walk into a pub and simultaneously identify the smells of chips, beer and sawdust - truly a complex chemical profile," Rotello said.
Persaud presented his results at the launch of the International Society for Olfaction and Chemical Sensing (ISOCS) in Nuremberg, Germany, on May 8.