Smartphones with electronic noses could sniff out dangerous chemicals

Smart phones can detect sound, light, motion, touch, direction, acceleration and even the weather—but they can't smell. It's a technological brick wall that companies and research institutes are trying to break through.

Partly, the problem is that we still don't understand well how humans and animals detect and interpret smells. The Nobel prize for understanding the principles of olfaction, or smell, was awarded only 12 years ago.

Scientists from the University of Leuven in Belgium are working on a solution that they hope could one day allow smart phones to detect different odours at minute levels; even spotting the early olfactory indicators of disease.

"The human nose can detect roughly ten thousand different smells, and that happens by a patch of skin at the back of your nose with specialised cells that send triggers to your brain. What we're trying to do... is to mimic the receptors on these cells, but the kicker is we actually have a much larger degree of freedom to design specific materials for molecules that you can't even smell," explained assistant professor Rob Ameloot.

The researchers have developed an 'electronic nose' in the form of metal-organic frameworks (MOFs)—microscopic structures, one-hundred-thousand times smaller than the diameter of a human hair. These act as 'molecular sponges', absorbing the molecules of a gas to trigger a reaction such as changing colour.

"What we're trying to do is tailor the pores of these materials so the molecule fits in there," added Ameloot.

So far, they've created MOFs consisting of organic molecules and metal ions that absorb phosphonates, found in pesticides and nerve gases. Postdoctoral researcher Ivo Stassen said their MOFs are the most sensitive sensors to date for these dangerous gases.

"The first step is we optimise the chemical synthesis of these materials and then we end up with a powder with the characteristics that we need," Stassen said, "the next challenge will be integrating these materials on solid [state] devices."

Transferring the sensing capabilities of their MOFs in powder form into a viable tool is the next hurdle the team in Belgium is working to overcome. However, depositing the MOF as a thin film over the surface of, for instance, an electric circuit is relatively straightforward, according to Ameloot.

"We've demonstrated these materials, they have the performance we want, we have the technology to deposit them as thin films. So the next step, the next stage in our research will be to actually make the device and to run this in the real world," he said.

At the Center for Surface Chemistry and Catalysis they're working on different MOFs custom-made to detect different molecules, including measuring the volatile organic compounds in a person's exhaled breath that could indicate disease. Eventually, they hope these could be easily integrated into electronic devices.

"What this would be is basically an electronic nose. And if you can integrate it in a small, robust format that's cheap enough you could have it in your smart phone to detect air quality to early diagnosis of early types of diseases," said Ameloot.

Such a device would mimic a dog's remarkable sense of smell which can detect minute odours known to be associated with volatile organic compounds produced by malignant cells. A recent UK trial showed dogs could detect the signs of prostate tumours in urine in 93 percent of cases. However, Ameloot said there are many limitations to using sniffer dogs in disease and explosives detection.

"A dog cannot give you a reading level, they can say 'yes' or 'no'. The same with 'this person has cocaine in their car'. But with a dog always comes a handler and since a dog is typically trained for only one or a few compounds you would need a whole lot of dogs and handlers to monitor air quality or to monitor for a terrorist attack," he said.

Numerous companies have attempted to build a powerful portable electronic nose over the past decade. Most have failed. Samsung Electronics was recently awarded a patent for an olfactory sensor that could be incorporated into any device - from a smartphone to an electronic tattoo - though this has yet to materialise.

The Cyranose Electronic Nose from company Sensigent is one of the few technologies to make it to market, and is designed to "detect and identify complex chemical mixtures that constitute aromas, odours, fragrances, formulations, spills and leaks."

However, Ameloot said the performance of the Cyranose and other such devices is inherently determined by the performance of the actual sensors inside. MOF-based sensors, he said, would improve the sensitivity and selectivity of current generation of sensors. — Reuters