The Mirica Group Designs an Electronic “Nose”

Katherine Mirica is an assistant professor of chemistry and head of the Mirica Group at Dartmouth College.

With an unlikely combination of tools—wooden pencils and a child’s arts-and-crafts kit known as Shrinky Dinks—Assistant Professor of Chemistry Katherine Mirica and her lab team are building an electronic “nose” to detect gases that are beneficial at some levels, but very dangerous at others.

“We are particularly interested in detecting and monitoring gases that may have an impact on health care but can also be environmental pollutants,” Mirica says. The “nose” they are developing is a portable sensing device that will detect the presence of gases.

The particular gases in her sights are nitric oxide, carbon monoxide, and hydrogen sulfide, all normally produced within the human body. In low concentrations, they can play a role in regulating the cardiovascular, neurological, and other life systems. With exposure to atmospheric pollution, or because of a metabolic imbalance, higher concentrations may form in the body. “These gases are essential to life, but if you have too much of them, they will kill you,” she says.

To explain how the device works, Mirica likens it to a human nose.

“When you smell a rose, you are actually sensing a variety of different things that tell you it is a rose—an array of chemical cues,” she says. With the device, “multiple sensors, each tuned to a different component chemical stimulus, must be employed. We ‘train’ this collection of multiple sensors to respond like a nose.”

The first step in her approach to sensor construction is to draw lines with standard pencils—the yellow wooden ones with graphite inside. Graphite conducts electricity, so the lines, which are drawn on a polymer (plastic) film, become their electrodes. This is followed by a process familiar to any child who’s played with Shrinky Dinks.

“Children bake plastic pieces in an oven, shrinking them down into small plastic charms, jewelry, and figurines,” says Mirica. “Similarly, we heat the film, which significantly shrinks the electrodes, allowing us to create miniaturized devices. While Shrinky Dinks works for toys, I do not think it has been previously used for making chemical sensors.”