The future of medical diagnostics is really exciting at the moment. In research, however, we keep coming back to old familiar knowledge, such as using the sense of smell for diagnostics – as the ancient Greeks already did. Even if nowadays doctors don’t sniff us themselves, we can probably rely on the sense of smell of man’s best friend, the dog.
The first publication that dogs can smell diseases dates back to 1989, when a dog sniffed and bit into a woman’s birthmark, which turned out to be skin cancer. In 2004, it became known that dogs can also sniff out bladder cancer in people’s urine. They are now thought to be able to identify diabetes (high blood sugar levels), breast cancer, malaria, and even infections with Covid-19 or the bacterium Clostridium difficile, Staphylococcus aureus, and Helicobacter pylori. They are able to do this because of their enormous number of olfactory receptors. Their diversity allows dogs to distinguish between many different compounds. The identification of impending asthma and epilepsy attacks is probably more due to slightly altered breathing rhythms.
We do not know exactly what the dogs smell. It is probably an odor pattern triggered by metabolic changes caused by a wide variety of diseases – probably also with specific disease signatures. The problem is that the odor difference is probably so subtle that even sophisticated analytical methods are too insensitive to distinguish between sick and healthy.
But man would not be man if he did not try to hand over similar abilities to an aid from technology: this aid is also partly biological – with bacteria.
Certain types of bacteria are able to grow tiny, electrically conductive so-called nanowires. These themselves serve to generate energy by transporting electrons along these nanowires and then transferring these electrons to iron, for example, at their end. Thus they can “breathe” and gain energy – without oxygen, which serves as a receiver of electrons. These nanowires are now also being modified to build small “power plants” that generate energy. In fact, a biofilm has been created from these bacteria that is capable of generating electricity from our sweat (its evaporation on our skin) on a long-term and continuous basis. So a small battery in the form of a microchip directly on our skin. The dreams now go so far that we could charge our cell phones with this “chip” on our skin.
But back to the sense of smell: How do the nanowires help us sniff out diseases? To do this, the bacteria are genetically modified so that a receptor for the substance to be sniffed out is anchored on the surface of these nanowires. When this substance binds to the surface, the current flowing through the nanowires on the microchip changes. This change can be detected and thus the presence of this substance can be inferred.
Will dogs be replaced in this way? At the moment definitely not yet, because so far there are only two substances that can be “sniffed out” by bacteria, and we are still a long way from the cocktail of smells that a dog can sniff out. In addition, there is another characteristic of the dog that cannot be replaced: In contrast to a bioelectronic detector, dogs can also fetch their mistress or master the packet of glucose if necessary, alert helping relatives and prevent their owner from crossing a road, for example, if danger is looming. This is possible because of their cognitive functions, communication, responsiveness and desire to belong. Other animals with a better sense of smell, such as elephants, bears, and sharks, would be unsuitable. And cats would probably also be unsuitable, as they would only give the required information on their own terms. Dogs, on the other hand, are such good partners that they always want to give us the information we need.