But now scientists and entrepreneurs are redoubling their efforts to recreate the sense of smell in compact devices that detect and analyze odors similar to the way cameras now recognize our faces and microphones our words. In pursuit of these high-tech devices–which could use odors to detect disease like cancer or Covid-19, locate hidden explosives or decipher our moods and behaviors--some companies are leveraging advances in synthetic biology and genetic engineering. Others are harnessing advances in artificial intelligence. "It's absolutely a growing field," says Andreas Mershin, an odor-sensor researcher at the Massachusetts Institute of Technology. He calls the field an "unexplored goldmine."

Numerous studies have shown that trained dogs can detect many kinds of disease -- including lung, breast, ovarian, bladder, and prostate cancers, and possibly Covid-19 -- simply through smell. In some cases, involving prostate cancer for example, the dogs had a 99 percent success rate in detecting the disease by sniffing patients' urine samples. But it takes time to train such dogs, and their availability and time is limited. Scientists have been hunting for ways of automating the amazing olfactory capabilities of the canine nose and brain, in a compact device. Now, a team of researchers at MIT and other institutions has come up with a system that can detect the chemical and microbial content of an air sample with even greater sensitivity than a dog's nose.

Most people consider smell their least important sense, surveys suggest. Dogs, however, feel their way through the world with their noses. Humans already employ the animals' olfactory acuity for contraband and explosives detection. More recently it has also proved uncannily good at sensing cancers, diabetes--and even COVID-19. Exactly how dogs detect diseases is a mystery, but that has not stopped researchers from mimicking this prowess with an artificial-intelligence-based noninvasive diagnostic tool.

Andreas Mershin visits with one of the trained disease-sniffing dogs in his office at MIT. The dogs are trained and handled in the UK by the organization Medical Detection Dogs. Trained dogs can detect cancer and other diseases by smell. A miniaturized detector can analyze trace molecules to mimic the process. Numerous studies have shown that trained dogs can detect many kinds of disease -- including lung, breast, ovarian, bladder, and prostate cancers, and possibly Covid-19 -- simply through smell.

Using powerful analytical tools including gas chromatography mass spectrometry (GCMS) and microbial profiling, "if you analyze the samples from, let's say, skin cancer and bladder cancer and breast cancer and lung cancer -- all things that the dog has been shown to be able to detect -- they have nothing in common." Yet the dog can somehow generalize from one kind of cancer to be able to identify the others. He envisions a day when every phone will have a scent detector built in, just as cameras are now ubiquitous in phones. Such detectors, equipped with advanced algorithms developed through machine learning, could potentially pick up early signs of disease far sooner than typical screening regimes, he says -- and could even warn of smoke or a gas leak as well. They then applied a machine-learning program to tease out any similarities and differences between the samples that could help the sensor-based system to identify the disease.