Researcher studying the chemistry behind airborne viruses

When the COVID-19 pandemic began, scientists across disciplines realized they were short on information about how aerosol particles transmit viruses. Paul Ohno, an assistant professor of chemistry and biochemistry in Auburn’s College of Sciences and Mathematics, was one of them.

“How many copies of a virus are in each particle? How do the properties of the aerosols affect virus transmission?” he asked. “People have been looking into these things for a long time, but there are many outstanding questions and not a lot of definite answers.”

Fast forward five years and Ohno is now halfway through a two-year project funded by the National Institutes of Health (NIH), studying the chemistry behind airborne transmission of viruses using fluorescence probe spectroscopy, a method of characterizing aerosol particles by exciting them with lasers.

With the help of students in his lab, Ohno is developing techniques and designing new instrumentation for characterizing aerosols so scientists can better understand how viruses are spread.

The science behind virus transmission

As an expert in aerosols, Ohno knows that people spreading illnesses emit particles of a wide range of sizes. During COVID, he began to wonder about the science behind masking and social distancing, which largely focused on six feet of distance between people.

“The six-foot rule works for larger droplets, because even if they escape the mask, they quickly settle down,” Ohno said. “But the smaller droplets get lofted much easier, and their settling time is more like minutes to hours, as opposed to seconds.”

While there are plenty of established techniques for studying larger particles, the toolbox for characterizing smaller particles is limited — one of the main motivations for the lab’s work.

Light it up

To identify the characteristics of those smaller droplets, Ohno and his students use fluorescence probe spectroscopy. They insert probe molecules into aerosol particles as they float through the air, and then, using instruments they’ve built themselves, they excite the particles with focused laser beams. The light that comes back out can tell them a lot.

“The probe molecules essentially change their color based on the properties of the environment they’re in,” he said. “Different colors of light are emitted depending on the particle’s pH, water content and viscosity.”

Studying these particle properties can help scientists identify their variability, both in what is produced by different activities — there’s variance in particles emitted from talking, shouting, singing and sneezing — and in humans, since some people just emit a higher or lower number of particles than others.

Ultimately, Ohno hopes that making these measurement techniques more widely available will help scientists better understand the connection between aerosol properties and virus transmission.

What’s a surface scientist?

Ohno, who calls himself “a surface scientist, aerosol scientist and spectroscopist,” has a mix of interdisciplinary science interests and expertise, and virus transmission is just one application area of his research.

Surface science is the study of the boundary region where any two substances come into contact with each other. Ohno studied the surface science of solids as an undergraduate student at Princeton University and then liquids while earning a doctorate from Northwestern University.

After researching aerosols as a Schmidt Science Fellow at Harvard University, it came time to settle down, and Ohno found Auburn’s Department of Chemistry and Biochemistry to be just the right fit.

“The department skews toward the early career side more than many other institutions,” he said. “There’s a lot of energy; people are building up their research programs, and there are a lot of exciting projects in areas of great recent interest to the wider scientific community.”    

Looking to the future

While the study of virus transmission often falls to virologists and epidemiologists, Ohno is enthusiastic that scientists from across disciplines can make significant contributions to the field of aerosol science. In addition to collaborating with others, he is hoping to eventually market the prototype instrument his lab has built to identify particle characteristics.

Currently, particle research is largely limited to a small number of labs with advanced technology. Ohno dreams of someday developing a portable and affordable instrument — something akin to a breathalyzer machine — that can be deployed to any medical facility or health department to monitor the spread of viruses in a community.  

“I want to make the instrument more compact and easier to use,” he said. “Wouldn't it be great if you could just breathe into something and it could tell you the number and properties of virus-containing aerosols you’re exhaling?”

While that goal may be far off in the future, NIH funding has enabled Ohno and his students to make significant advances.  

“My research group is definitely not going to solve these huge questions by ourselves,” he said. “But we’re developing these techniques and instruments with the hope that someday we can address deficiencies in understanding the connections between aerosol properties, virus transmission and, ultimately, public health.”