So your nose is a super sniffing machine able to tell the difference between 4,000 and 10,000 different odors. Your nose has about one-hundred million tiny special things called receptors that can bind a particular odor molecule (such as the molecule allicin shown below, which gives garlic its smell) and then when it does bind, it sends a signal to your brain and then your brain tells you what you smelled.

Can scientists build a fake nose? Well sort of. What you need is some kind of part that would be able to bind different odor molecules and then wire that up to something that would transfer a signal to a computer which might act as a brain. The thing that transfer the signal is pretty simple. A special class of transistors, called ‘field effect transistors’ are sensitive to their environment. They can ‘sense’ changes in their environment. When something in their environment changes (like a new molecule is introduced) then their ability to conduct electricity changes. If you can measure how much electricity is going through one of these transistors then you measure what the transistor is sensing. That is the easy part.

The harder part is making a transistor specific for an odor molecule. In your nose, the mucus layer helps protect the receptors but allows molecules to diffuse in. To make a fake nose, scientists use different kinds of films like plastic wrap. This is a special kind of plastic wrap because it only lets certain kinds of molecules to pass through. Cover one of these field effect transistors in plastic wrap and you can build a sensor that can ‘smell’ one kind of odor molecule. Do the same thing with a different kind of plastic wrap and you have another. And again and again until you have a couple of thousand different kinds of odor sensors. Then maybe you have a fake nose. Sound crazy? Well there are a number of groups trying to do just that. Making fake noses for things like ‘smelling’ diseases, or maybe even dangerous stuff like bombs. One important thing about these fake nose is that they never get tired or get stuffy. So they are smelling all of the time.

Image Sources: University of Maryland | Chemical Technology | 3Dchem