According to the researchers, the new flexible, porous, and highly sensitive nitrogen dioxide sensors that can be applied to skin and clothing have potential applications in healthcare, environmental health monitoring, and military use.
Led by Huanyu “Larry” Cheng, an assistant professor of engineering science and mechanics at Penn State, the researchers have published their sensor designs, which build on previous models, and come up with Applied materials and interfaces ACS.
The sensors monitor nitrogen dioxide, either from the breath if attached under the nose, or from the sweat if attached elsewhere on the body. Unlike blood sample collection, direct attachment to the skin allows for continuous, long-term gas monitoring.
Cheng explained that while similar sensors exist, a key differentiator for the new design is breathability.
“Commonly used substrate materials for gas sensors are flexible, but not porous,” he said. “The accumulation of moisture from water on the surface of the skin can potentially lead to irritation or damage to the surface of the skin. We must ensure that the device can be porous so that moisture can pass through the sensor without accumulating on the surface.”
The researchers created the new sensors using a manufacturing method known as direct laser writing.
“Laser direct writing is similar to additive manufacturing in that it’s easy to set up and low cost, and laser is widely available,” Cheng said. “The process is relatively robust, fast, and could be scaled up to large-scale manufacturing.”
Cheng and his team integrated a type of material known as block copolymers with resin into laser-writing sensors with the desired breathability.
“The integration of block copolymers goes beyond the materials we were using, so we explored extending the substrate material from the typical thin film to virtually anything,” Cheng said. “It can give us breathability and the ability to adjust pore size.”
Cheng said the sensor could monitor conditions such as chronic obstructive pulmonary disease, which nitrogen dioxide can cause or worsen. He also noted that although the sensors were developed specifically to detect nitrogen dioxide, they could potentially detect a variety of gases and biomarkers – to determine glucose levels to monitor diabetes, for example, or to identify hazards in industrial or combat environments.
“Sensors can also be useful for monitoring gases in the environment,” he said. “We could monitor air quality and notify patients of potential concerns about too much car exhaust, for example. Then they could use that information to avoid certain areas on certain days.”
The other authors of this article are Li Yang, Huadong Ji, Chuizhou Meng, Guanhao Zheng, Xue Chen, Guangyu Niu, Jiayi Yan, Ye Xue and Shijie Guo, all from Hebei University of Technology in Tianjin, China; and Yuhang Li from Beihang University in Beijing. The National Natural Science Foundation of China, Hebei Province Key Research and Development Project, National Science Foundation, National Institutes of Health, and Penn State funded this work.