Super-sniffer mice have a nose for explosives or disease

Mammals detect smells through a series of sensory neurons and receptors in the nose. Receptors are tuned to specific odors, and the attached neurons transmit the signal to the brain for processing. 

You'll find a fairly even distribution of different receptors in any given mammalian nose, but we don't quite know how our DNA tells the neurons which receptors to "choose" as our olfactory system develops.

"This is one of our five basic senses, yet we have almost no clue how odors are coded by the brain," says Professor Paul Feinstein of Hunter College at City University of New York. "It's still a black box."

In an attempt to better understand the mysteries of our noses, the researchers experimented with the mouse genome, injecting DNA containing a specific odor receptor into a fertilized egg cell, along with extra DNA strings to alter the probability of the gene being chosen. After a few attempts, the result was a series of mice with olfactory systems that contained more receptors tuned to detect the smell of the compound acetophenone, along with a fairly even distribution of other receptors.

The team tested for this by exposing the mice to that specific odor, and using fluorescent imaging found that the desired receptor was present in larger amounts than usual. In practice, the mice were trained to avoid an odor that binds to those receptors. When presented with that odor in water, the engineered mice were able to detect it at levels two orders of magnitude fainter than control mice.

Potential applications for the super-sniffing mice include training them to detect explosives, and diagnosing disease. The team is currently commercializing the technology through a company called MouSensor.