'Biohybrid' sensor can detect chemical odours

A keen sense of smell is a powerful ability shared by many organisms, but it has proven difficult to replicate by artificial means. Now, Japanese researchers have combined biological and engineered elements to create a volatile organic compound sensor that has the ability to detect odours in gaseous form. Their research has been published in the journal Science Advances.

As noted by Professor Shoji Takeuchi, from the Biohybrid Systems Laboratory at The University of Tokyo, “Odours — airborne chemical signatures — can carry useful information about environments or samples under investigation. However, this information is not harnessed well due to a lack of sensors with sufficient sensitivity and selectivity.

“On the other hand, biological organisms use odour information extremely efficiently. So we decided to combine existing biological sensors directly with artificial systems to create highly sensitive volatile organic compound (VOC) sensors. We call these biohybrid sensors.”

Prof Takeuchi and his team essentially grafted a set of olfactory receptors from an insect into a device that feeds certain odours to the receptors and also reads how the receptors respond to these odours. Analysis of electrical signals from the olfactory receptors indicates what molecules triggered the signals. This method yields great sensitivity and is possible thanks to the way the receptors are physically bound within lipid bilayers. In previous experiments such a method has limited the way odours can be delivered to the receptors, but the team created an efficient solution to this problem too.

“The receptors react to molecules in a liquid droplet, so one of the main challenges was to make a device to transplant molecules from the air into these droplets,” Prof Takeuchi said. “We designed and fabricated microscale slits underneath where the droplet passes to force this exchange of molecules. By introducing the gas into the microslit, we were able to increase the probability of contact between the gas and the droplet and transfer target molecules to the fluid efficiently.”

With this system, the researchers were able to detect traces of the chemical octenol (or mushroom alcohol), which is known to attract mosquitoes, in the breath of a test subject. The VOC sensor could also detect concentrations in the order of parts per billion — about a thousand times less than the sensitivity of a dog’s nose, but enough to inspire the team to keep innovating.

“I would like to expand upon the analytical side of the system by using some kind of AI,” Prof Takeuchi said. “This could enable our biohybrid sensors to detect more complex kinds of molecules. Such refinements might help in our goals to not only measure hazardous materials and environmental hazards but maybe even early stages of diseases from patients’ breath and body odour.”

Image caption: Design of the VOC sensor. Image ©2020 AAAS/Takeuchi et al.

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