Blindfolded, would you know the smell of your mom, a lover or a co-worker? Not the smells of their colognes or perfumes, not of the laundry detergents they use — the smells of them?
Each of us has a unique “odor print” made up of thousands of organic compounds. These molecules offer a whiff of who we are, revealing age, genetics, lifestyle, hometown — even metabolic processes that underlie our health.
Ancient Greek and Chinese medical practitioners used a patient’s scent to make diagnoses. Modern medical research, too, confirms that the smell of someone’s skin, breath, and bodily fluids can be suggestive of illness. The breath of diabetics sometimes smells of rotten apples, experts report; the skin of typhoid patients, like baking bread.
But not every physician’s nose is a precision instrument, and dogs, while adept at sniffing out cancer, get distracted. So researchers have been trying for decades to figure out how to build an inexpensive odor sensor for quick, reliable and noninvasive diagnoses. The field finally seems on the cusp of succeeding.
“You’re seeing a convergence of technology now, so we can actually run large-scale clinical studies to get the data to prove odor analysis has real utility,” said Billy Boyle, co-founder and president of operations at Owlstone, a manufacturer of chemical sensors in Cambridge, England.
The sensor is a silicon chip stacked with various metal layers and tiny gold electrodes. While it looks like your mobile phone’s SIM card, it works like a chemical filter. The molecules in an odor sample are first ionized — given a charge — and then an electric current is used to move only chemicals of diagnostic interest through the channels etched in the chip, where they can be detected.
A similar diagnostic technology is being developed by an Israeli chemical engineer, Hossam Haick, who was also touched by cancer.
His smelling machine uses an array of sensors composed of gold nanoparticles or carbon nanotubes. They are coated with ligands, molecular receptors that have a high affinity for certain biomarkers of disease found in exhaled breath.
Once these biomarkers latch onto the ligands, the nanoparticles and nanotubes swell or shrink, changing how long it takes for an electrical charge to pass between them. This gain or loss in conductivity is translated into a diagnosis. “We send all the signals to a computer, and it will translate the odor into a signature that connects it to the disease we exposed to it,” Mr. Haick said.
Mr. Haick and his colleagues published a paper in ACS Nano last December showing that his artificially intelligent nanoarray could distinguish among 17 different diseases with up to 86 percent accuracy. There were a total of 1,404 participants in the trial, but the sample sizes for each disease were quite small. And the machine was better at distinguishing among some diseases than others.
The team chose plasma because it is somewhat less likely than breath or urine to be corrupted by confounding factors like diet or environmental chemicals, including cleaning products or pollution.
Instead of ligands, their sensors rely on snippets of single-strand DNA to do the work of latching onto odor particles. “We are trying to make the device work the way we understand mammalian olfaction works,” said Charlie Johnson, director of the Nano/Bio Interface Center at the University of Pennsylvania, who is leading the fabrication effort. “DNA gives unique characteristics for this process.”
“My estimate is it’s a three- to five-year time frame” before such tools are available to clinicians, she added.