Oxygen, nitrogen and carbon dioxide — there are plenty of gases and particles in the air that freely enter the body. Many of them are considered toxins and pollutants that can harm organs and increase health risks. Yet, there are few efficient and affordable ways of monitoring these chemicals in the air.

A trio of scientists is looking to change that.

University of Wisconsin chemical and biological engineering professors Nicolas Abbott and Manos Mavrikakis are trying to develop cheap, small and lightweight sensors to monitor air and human health quality. Abbott and Mavrikakis are working alongside Robert Twieg, a chemistry and biochemistry professor at Kent State University, and look to use liquid crystals for chemical sensing.  

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Unlike water, liquid crystals have a longer range of interaction, which forms a key property of the sensor, Abbott said. When water molecules interact with each other, they can only do so over a molecular length or two, which is approximately one nanometer, he said.

In liquid crystals, molecules move and flow around like in a common liquid, but the nature of their interactions is such that they “talk to each other” over very long distances. So molecules will interact with each other over distances of about 100 micrometers, which is about 100,000 molecular lengths, Abbott said.

Abbott said sensors detect toxins based on interactions between liquid crystals. The first layer of the sensor is metal salts, over which lies a layer of liquid crystals. These crystals are in a specific composition and orientation that enables the molecules of the targeted toxin to attach to the surface, he said.

When a toxin attaches itself, it displaces or moves around some of the molecules already present on the surface, Mavrikakis said. As a result, the liquid crystals change their appearance, which helps indicate the toxin’s levels in the air. The trio is currently working on developing ideal surfaces to do this job.

“The surfaces are like airports, targeted toxin molecules are airplanes in the air wanting to land, liquid crystals are the stationary airplanes already occupying the landing belt,” Mavrikakis said. “For an airplane to land, the stationary one has to move or displace and that is more or less … what we want in our experiments.”

Using liquid crystals for sensors is fairly common among researchers. But Abbott, Mavrikakis and Twieg have a special methodology that sets them apart.

Mavrikakis makes some predictions, Twieg makes the molecules and hands them off to Abbott, who tests whether the computational predictions are correct. Information on findings is fed back to Mavrikakis’ group, which then refines their methodologies.

This feedback loop is key to this group. They are trying design materials through computation and developing methodologies to accelerate materials’ discovery process, Abbott said.

“But the methodology [feedback loop] that we are using here at UW is unique,” Mavrikakis said. “We are ahead of everybody else.”

One of the most interesting aspects of these sensors is that they could be incorporated into smartphones in the future. The technology used in smartphone displays is similar to that of the sensors, Abbott said.

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Abbott said the technology is “complicated” but a necessity. The health risks associated with several molecules in the environment are unknown because there is no way to detect them.

Assessing the effects of personal exposure, for example to volatile organic chemicals like gasoline, requires measuring the extent to which the individual is exposed to them, Abbott said. That can only be done through sensors that stay with the person throughout a particular period of time.

“You can’t just put a sensor in a corner of a building because it doesn’t tell you what the environment around the person is,” Abbott said. “The sensor has to go with the person.”

One possible application of the sensor is for asthma detection. Medical experts have debated using something to look at nitric oxide concentration in human breath, which is an asthma indicator, Abbott said.

Another use for these sensors is to better and more accurately monitor pollutants like carbon monoxide, sulfur dioxide and ozone. Unmanned vehicles like drones could carry these sensors, Abbott said.

“All we need is to leverage technology,” Abbott said.

Other than in environmental monitoring and human diagnostics, these sensors can be used in food packaging to assess the freshness of the food items, especially meats and seafood, Mavrikakis said.

Currently, the sensor is available in the market as a badge-sized dosimeter, which is a device that measures exposure to radiation. It displays whether or not the wearer has been exposed to hydrogen sulfide in accordance with Occupational Safety and Health Administration limits over an 8-hour period, Mavrikakis said.

The alternative to this badge is much more expensive, requires more effort and is not convenient to use. It also reports exposure levels much more slowly than the badge.

Platypus Technologies, the company that created the badge, is working on integrating the sensor with smartphones. This would allow the smartphone to pass data to a central industrial hygiene lab and fill a database with information on toxin levels, Abbott said.

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Relatively low numbers of toxins can be detected at the moment, but the trio hopes their research can help detect all of the pollutants within the next ten years, Mavrikakis said.

“If you identify the key principles, there are plenty of opportunities, as the computational power is growing and becoming cheaper,” Mavrikakis said.