Canines still take the lead when it comes to sniffing out smells. But the latest research shows that machines are closing the gap.
With any luck, you’ve never been stopped on the road and asked to take a breathalyser test – a piece of technology that’s enough to get you arrested. This simple “electronic nose” detects alcohol in your breath. But if a sniffer dog jumps out of the police van, it could go a step further, uncovering tiny traces of drugs or explosives.
The ever-improving technology of e-noses is getting much closer to the accuracy of dogs and other animals. Such devices are increasingly able to recognise and interpret a range of gases to report meaningful information. The next few years could see an e-nose explosion as sensor technology rapidly improves (see box below).
By Line Emilie Fedders
Studies have found that mice whose grandparents learned to associate the smell of cherry blossoms with pain are scared by the same smell, possibly due to epigenetic changes.
The pheromone conundrum
Pheromones are highly debated in human biology. Scientists have identified several molecules that appear to influence other persons, but they could not demonstrate if and how they are used by our body to communicate.
The ingestion of 35 millilitres of vodka made subjects in a 2014 study better at detecting smells. But beyond that amount, things went downward quickly.
Dogs sniff out cancer
Several studies have shown that in addition to money and drugs, trained dogs can detect prostate, ovarian or gastrointestinal cancer from urine samples.
Tracking criminal activity
Crim-Track is a major European project that uses new nanotechnology to identify suspicious fumes quickly and cheaply in such places as airports, with the aim of sniffing out criminals. Its e-nose relies on the technique of calorimetry, which is able to detect very low concentrations of volatiles in the air – the “smells” of a wide variety of chemical compounds.
Jens Kristian Munk of the Technical University of Denmark (DTU), one of the partners in Crim-Track, hopes that their e-nose can become the “first line of defence against trafficking of drugs and explosives.” He adds that the device could be “trained” to track down anything from money to foodstuffs more reliably than sniffer dogs. Field tests will begin in 2016.
Researchers at the Universidad Politécnica de Madrid (UPM) and Spanish start-up SEADM believe that body odour can be used as a biometric to add robustness to a biological identification system.
“Advances in technology have made possible the advent of non-invasive sensors to capture body odour,” explains researcher Irene Rodríguez-Luján of UPM. “Our e-nose could be used to effectively increase the reliability of well-known techniques, such as fingerprints and iris scans.”
Although the team’s technology has a promising recognition rate of 85 per cent, they are, according to Rodríguez-Luján, “still a long way from achieving the accuracy of dogs’ sense of smell”.
Much e-nose research focuses on detecting diseases, especially conditions for which current tests are expensive, insufficiently accurate or unpopular with patients.
U-BIOPRED is a project funded by the European Commission and the pharmaceutical industry to develop new treatments for severe asthma.
“We’ve learnt that there are about 3,000 molecules in exhaled breath, which vary by disease state,” says Peter Sterk, a clinical physiologist at the University of Amsterdam. “An e-nose doesn’t identify the individual molecules, but recognizes mixtures of molecules as a pattern, much in the same way our own noses do.”
Early trials have shown that U-BIOPRED’s e-nose could diagnose patients and pinpoint asthma subtypes so as to predict the effectiveness of therapy – all in real time and at point of care.
The team are creating a “breath cloud” that can be shared by doctors around the world to exchange data. This database will prime each e-nose to recognise new disease subtypes. The need to account accurately for environmental changes – correcting for recent meals, for example, or for patients who smoke – is an ongoing challenge.
“It may not be the golden bullet,” says Sterk, “but we’re making good progress. I have no doubt that this cheap, point-of-care technology will get into the doctor’s office for diagnosing and monitoring patients.”
The robot fly
Martin Strauch of the University of Konstanz studies the neurobiology of how insects process odours. He hopes to integrate the high sensitivity and wide-ranging odour receptors of flies into biotechnological sensors capable of sniffing out deadly diseases.
Strauch and his colleagues have gathered real-time responses from odour receptors in the antenna of a living fruit fly. Using calcium imaging to measure the activity of neurons inside the antenna, they have shown that “the fly’s responses can tell the difference between healthy and cancerous cells,” he says.
This work is the first step towards equipping e-noses with biological sensors, giving them a much wider receptive range. It would produce standardised odour responses that could be measured with less chance of error. The goal is to improve on the amazing capabilities of sniffer dogs, whose behaviour is still subject to interpretation.
Sensor arrays inside e-noses react to volatile organic compounds (VOC) – vapours or gases at room temperature. As these chemicals settle on a sensor’s surface, they trigger a physical change in the sensor, which is recorded electronically. Each sensor will respond strongly or weakly to each VOC, creating a pattern of response called a fingerprint.
An integrated computing system combines the responses from all of the sensors, analysing them together. It compares the resulting pattern to a “smell database” to report on what it has found.
E-noses are being developed to recognise an odour as a whole entity, rather than picking out its constituent chemicals. This, in general, mimics the biological sense of smell.
E-NOSES IN ACTION
To avoid dodgy dinners
Connected to a smartphone, the Peres device reports whether food is safe to eat by detecting vapours that indicate to decomposition.
To identify hospital superbugs
A University of Leicester prototype speedily identifies specific strains of Clostridium difficile from the combination of 69 possible volatile organic compounds released by the bacteria, allowing targeted treatment.
To expose counterfeit eggs
An e-nose developed by scientists at China’s Huazhong Agricultural University can distinguish the eggs of seven birds to authenticate pigeon eggs, a popular meal.
To care for astronauts
NASA’s e-nose continuously monitors the International Space Station for contamination by such chemicals as mercury, ammonia and methanol.
To suss out strange smells
Coffee can smell like potato when roasted, but an e-nose in development by Nosang Myung at the University of California, Riverside could identify a bad bean before it ruins the batch.
By Holly Cave