Huanyu “Larry” Cheng, the James L. Henderson Jr. Memorial Associate Professor of Engineering Science and Mechanics, and his team have created a new water-resistant gas sensor that enables accurate, continuous monitoring of nitrogen dioxide and other gases in humid situations.
The sensor picks up nitrogen dioxide in breath, which can be used to monitor air quality or to identify potential respiratory disorders based on concentration. The team’s approach was published in Microsystems & Nanoengineering.
Cheng previously created a waterproof sensor, but it could only sense temperature and motion. In addition, Cheng has created a flexible, porous, and sensitive gas sensor as well as a microscale gas sensor that can be completely customized.
However, exposure to moisture from perspiration, humidity, or other sources rendered the sensors useless.
“We cannot avoid humidity levels in the environment, which is why we wanted to emphasize the moisture-resistant property,” Cheng said.
The same laser-induced graphene (LIG) fabrication technique that uses laser writing to form two-dimensional graphene layers was employed by the researchers to create the prior gas sensors. LIG is quick, economical, and environmentally benign.
This time, they supplemented the LIG sensing layer with a soft elastomeric polymer substrate and a moisture-resistant, semi-permeable membrane.
This sensor could be used for the early screening process, to make someone aware of the potential condition that may develop into a bigger concern later, and also for the existing COPD or asthma patient to monitor the environment for potential exposure to nitrogen dioxide so they can take early prevention measures, like avoiding certain areas with higher nitrogen dioxide levels.
Li Yang
“Laser-induced graphene is hydrophilic, so it intrinsically is a water-absorbing material,” Cheng said. “Water will naturally get down into the material and change its properties. If you have water molecules absorbed by the sensor, that will change the response. By using a semi-permeable membrane with the LIG, we can block the water or moisture from the outside but still allow the permeation of the target gas molecule. Since the new material is stretchable and soft, it can be worn on the skin for a long time without causing irritation.”
The sensors were put to the test by the researchers as they measured the breath of 30 people. They discovered that patients with chronic obstructive pulmonary disease (COPD) or asthma had sensor response values that were more than four times higher than those of patients without these conditions, indicating that these patients exhaled nitrogen dioxide at a rate that was more than four times higher.
“With this sensor, we are much closer to the actual application of helping a patient,” said co-author Li Yang, associate professor in the School of Health Sciences and Biomedical Engineering at Hebei University of Technology.
“This sensor could be used for the early screening process, to make someone aware of the potential condition that may develop into a bigger concern later, and also for the existing COPD or asthma patient to monitor the environment for potential exposure to nitrogen dioxide so they can take early prevention measures, like avoiding certain areas with higher nitrogen dioxide levels.”
According to Cheng, this sensor may someday be utilized to monitor not only a person’s well-being but also to learn more about the general health of a population.
“This could be used for a large-scale study to provide information that was previously inaccessible with the other type of sensor devices, which is something I’m excited about,” he said.
In addition to these Penn State institutions, Cheng also has links with the Materials Research Institute, the Institutes of Energy and the Environment, the Institute for Computational and Data Sciences, the College of Earth and Mineral Sciences, and a number of engineering departments.
The other authors on the paper are Ye Xue of the School of Health Sciences and Biomedical Engineering at Hebei University of Technology in China; Guanghao Zheng, Chuizhou Meng, Huadong Ji and Jiayi Yan of the School of Mechanical Engineering at Hebei University of Technology in China; Yaoqian Cao of Tianjin Medical General Hospital in China; Yuhang Li of Beihang University in China; Xue Cheng of the School of Electrical Engineering at Hebei University of Technology; and Guangyu Niu of the School of Architecture and Art Design at Hebei University of Technology.
The National Science Foundation, the National Institutes of Health, Penn State, the National Natural Science Foundation of China and the Key Research and Development Project of Hebei Province funded this research.
