Following on the tails of fitness trackers, there has been a push to develop personal environment monitors—a new breed of wearable tech that collects data on airborne toxins and communicates it to users. A group of researchers at RMIT University in Australia has taken a significant step in this direction, creating thin, flexible sensors that can be placed on your skin or in your clothes to track exposure to hazardous gases and UV rays.
“We were interested in making a device that could detect dangers that are generally not recognized by our senses,” says Philipp Gutruf, the lead author of a recently published study. “These dangers are often not really severe if noticed early enough, but become really dangerous when you are exposed to the hazard for too long.”
The trick was making stretchy electronics that could bend without breaking. Gutruf and his team first dug into the material science, and then worked on incorporating the environmental sensors. They printed semiconductors on super thin films made of cheap, readily available elastomeric polydimethylsiloxane, a type of silicone they'd worked with in previous studies. Then, they stacked these films in layers, so that if a single layer broke the whole thing wouldn’t shatter.
“We can make brittle materials stretch and bend using a technology called micro-tectonics,” Gutruf says. “This novel effect relies on overlapping thin films in a fashion very similar to tectonic plates that form the Earth’s crust. This technology allows us to bring the key ingredients for electronics to a stretchable platform.”
Once they determined the material, the researchers looked at how to use the films to sense hazardous gases, like hydrogen and nitrogen dioxide, and to react to harmful UV rays. They inserted thin layers of reactive oxides into the silicone, so that the sensors could register the gases, but still be flexible and stretchy enough to be incorporated into a piece of clothing or a patch that sticks onto skin.
For instance, the researchers coated the UV sensors with zinc oxide, the active ingredient in sunscreen. When exposed to light, the zinc oxide charged the sensors. “The UV sensors work by absorbing the UV radiation, such as rays from the sun, which makes the device more conductive,” says Gutruf.
The gas sensors work similarly. They’re geared for specific gases, and when they’re exposed to high levels of a certain gas—nitrogen dioxide, for instance—they carry a charge. “The conductivity rises or decreases based on the type of gas that is present in the surrounding atmosphere,” he says.
In the future, the stretchy patches could be used to prevent sunburns or to predict asthma attacks, but they also have potential to be lifesaving in places like mines or coal-fired power plants where high levels of gases can be toxic. The EPA is experimenting with similar technology. Nanosensors are becoming a part of the agency's mine remediation projects and other cleanups, because they can be implemented cheaply, quickly and in a lot of places.
"In recent years, nanotechnology has risen to the forefront and the new properties and enhanced reactivities offered by nanomaterials may offer a new, low-cost paradigm to solving complex environmental and engineering problems," Madeleine Nawar, project officer at the EPA's radiation protection division said in a report.
So far, Gutruf's sensors have only been tested in the lab. He suspects it will be four years before the sensors are available commercially, but the possibilities for tracking environmental pollutants with them are endless.
“In principle, almost all known substances can somehow be detected,” he says.