In this 21st Century Chemist profile, California Institute of Technology chemist Nate Lewis explains his work developing an artificial, electronic "nose" that can read odor patterns to detect and distinguish odors.
Odor Reader Chemist Works to Develop Artificial Nose
TOM COSTELLO, reporting:
It is one of the most dynamic and mysterious of our senses - not sight, sound, touch or taste, but smell, also known also as olfaction. For nearly twenty years, Nate Lewis and his team at the California Institute of Technology have been developing an electronic nose, or e-nose, to reproduce in a man-made device the amazing chemical sensitivity of the human nose.
DR. NATE LEWIS (California Institute of Technology): We have as humans about a thousand different genes all devoted just to using the sense of olfaction and smelling in our nose. We have about a million odor receptors. What we don't do is have one receptor for your teacher that lights up when your teacher comes into the room or when your best friend comes into the room.
COSTELLO: When the human nose detects a smell, molecules from the odor travel down the nasal passage and bind to odor receptors lining the nose. But there are many unanswered questions about how the brain interprets the different odor patterns of say, a rose, or a clove of garlic, or a carton of spoiled milk.
LEWIS: In olfaction, unlike vision, you can't tell me quantitatively whether something smells twice as intense. But you can see something as twice as bright. You can tell me it's red or green or blue, but you can't really tell me it smells anything other than good or rotten.
COSTELLO: To better understand how the brain interprets different odor patterns, Lewis, a materials chemist funded by the National Science Foundation, created this...
LEWIS: I wanted to build something that would allow us to study how a nose could work based on patterns of different people, of different molecules, of bad smelling compounds versus pleasing smelling compounds and so we went back to the lab and built a pattern-based electronic version of what we thought the human nose was doing.
COSTELLO: While the electronic nose is engineered to act like a human nose, it hardly looks like one.
LEWIS: So this is a little bit bigger than your nose, but not too bad.
COSTELLO: For Lewis, some of his biggest moments of inspiration don't happen in his science lab. The idea for the e-nose happened while he was strolling along a California beach.
LEWIS: I saw a dog on the beach and I wondered how did that dog know who their owner was and who I was when they'd never smelled me before? They couldn't have a specific receptor for me because just like a key going into the house they didn't know my code. That was the moment that I said there must be something different here, something really interesting here for us to go back and build in the lab.
COSTELLO: Lewis and his team started with what they knew about odor recognition. As odor molecules bind to the receptors, they create odor patterns that are then sent to the brain to be unlocked or recognized as different people, places and things.
LEWIS: In our human nose, we use proteins to bind odor molecules and then generate different odor patterns. We built an electronic nose that works the same way, but doesn't use proteins. It uses thin films that swell like little sponges. Each little sponge swells differently when an odor is present and the pattern of those different swellings lead to our ability to do different smellings with those arrays of receptors.
COSTELLO: Each sponge is made up of a material whose electrical properties change as a function of the degree of swelling. Lewis and his team of graduate students are on a mission to detect and analyze these odor patterns. In the lab, they test the main chemical component of the electronic nose, the polymer sensors, with different odor vapors.
LEWIS: Every one of the sensors has a different chemical sponge. The different smellings on these different sponges make a pattern of currents that we read in every one of those wires, send it to the computer and then it displays those different sponge patterns for every different smell.
COSTELLO: Finding and identifying the patterns of specific odors can provide important information for public health and safety - distinguishing between fresh and rotten produce, for example, or detecting which harmful chemicals might be in the air.
LEWIS: For the military it's really important to know whether or not a terrorist would release a bad chemical warfare agent and when and how to suit up. It will be good for homeland security to know whether or not there was something bad in the subways or at the football stadiums.
COSTELLO: The e-nose has even been to space - twice! It traveled on the Space Shuttle Discovery in 1998, along with legendary astronaut John Glenn, to collect and analyze air samples in the middeck of the shuttle. It returned to space in 2008 on the Space Shuttle Endeavor to monitor the environment on the International Space Station. In these cases, the e-nose was designed to trigger an alarm if it detected the presence of hazardous odors that might have accidentally leaked into the parts of the Space Shuttle or Space Station where people lived and worked.
LEWIS: It would detect when they were cooking their food and some other incidental odors that were routine, but fortunately it never alarmed at any of the hazardous odors.
COSTELLO: Having found the sweet smell of success in both outer space and on planet Earth, Lewis knows chemistry is all about hard work, intuition, and a little bit of luck.
LEWIS: No matter how smart we are you have to be in the right place at the right time and then you can add up the pieces and follow your nose to find something new.
To hunt for tiny whiffs of life on Mars, NASA scientists want to follow a mechanical nose. It is a far cry from the schnozz on your or my face, but instead a perceptive laser sensor already employed by the military to detect biological threats.
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