By Dustin Renwick
EPA scientists monitor pollutants with odd names, but benzene stands out as one of most widely used chemicals in U.S. The compound ranks as a human carcinogen and an air pollutant found in sources including gasoline, vehicle exhaust and cigarette smoke.
Current commercial benzene monitors work well, but the equipment is cumbersome and expensive. On the other hand, the cheap, portable technology that could allow you to test multiple highways in a day isn’t yet accurate enough for scientific research.
EPA organized a challenge for inventors and developers to help make benzene detection easier and less costly.
“One of our jobs is to communicate to the general public and those who are involved in new technologies what our interests are,” said Ron Williams, an EPA research chemist who worked on the team that designed the challenge.
The competition’s prize was recently awarded to Doug Corrigan, who has experience in physics, biochemistry and materials sciences and now works with technology-based economic development.
He said his experiences with different fields give him a figurative toolkit with pieces that sit ripe for remixing.
“It’s always satisfying to look at something and say, I have no clue how we’re going to work through that,” Corrigan said. “These challenges force you to sit down and learn new things.”
How He Did It
Corrigan’s solution used molecularly imprinted polymers (MIPs) and the measurement sensitivity of carbon nanotubes.
What does that mean?
If you created a mold of a raspberry pressed into wet plaster, you’d have a unique indentation. Other berries without that exact size and structure wouldn’t fit — similar to how a key pairs with its matching lock.
The same thing happens in MIPs, where scientists stamp a “key” compound, such as benzene, into a polymer. After the initial template is removed, benzene is the only molecule that will match that imprint, the “lock.”
Scientists also need a way to know when the key is in the lock, indicating benzene’s presence.
Nanotubes can measure small changes in electrical current, such as when a benzene molecule attaches to the MIP. Imagine rolling a sheet of chicken wire, and you have a good proxy for a nanotube, except the wall of a nanotube is one carbon atom wide. In this form, carbon exhibits those electrical properties not found in the graphite of pencils or the 3-D structure of diamonds.
But nanotubes don’t work well by themselves in air sampling monitors because too many gases create an information overload. In Corrigan’s design, the MIPs select the specific compound scientists want the nanotubes to measure.
The sensor arrangement can return measurements within a few minutes, and it all fits in a cost-effective package about the size of a large shoebox.
“When you consider the potential of molecularly imprinted polymers and carbon nanotubes for benzene sensors, that’s something you can fabricate,” said Eben Thoma, an EPA research scientist. “That’s mass production with a much lower cost potential.”
The EPA is now exploring methods for building prototypes of Corrigan’s design and transferring the technology to the public sector.
About the author: Dustin Renwick works as part of the innovation team in the EPA Office of Research and Development.