The researchers used graphene foam to develop independent sensors

An international collaboration led by Penn State University has developed a self-powered, self-contained sensor system capable of monitoring gas molecules in the environment or in human breath. The system combines nanogenerators with tiny supercapacitors to capture the energy generated by human movement.

The researchers' technique should cost only a few dollars in materials and use of widely available equipment. The development is the culmination of Penn State Memorial Associate Professor of Engineering Science and Mechanics Huanyu "Larry" Cheng, James L. Henderson Jr. The culmination of years of leadership.

"This is really a combination of previous studies where we continue the journey of developing wearable gas sensors," Cheng said. "Most sensor research and development is focused on the fabrication of device materials. Here, we use one material to produce multiple components on a single platform that work together as a separate system."

Cheng and his team previously developed sensors to detect nitrogen dioxide, which can indicate various lung diseases in exhaled gases, as well as other gases that may indicate poor ambient air quality. They have also created a laser-induced graphene foam material that contains MXenes, two-dimensional transition metals that are less active than other metals. This novel material and new manufacturing methods result in an elastic sensor that bends with human movement. The researchers are also using the method to produce tiny, retractable supercapacitors that can store the energy generated by these human movements.

In their recent work, the group has combined these efforts. They first applied the laser to a 3D porous graphene foam on a previously developed flexible substrate. Next, the researchers sprayed MXenes onto the graphene foam and used another laser to combine the foam and MXenes into a nanocomposite. They then transferred the nanocomposite into a pre-strained elastomer, which was slowly released. This slow release allows nanocomposites to shrink, allowing different patterns to be designed for sensors, nanogenerators and tiny supercapacitors.

"Using this laser is almost like baking a piece of bread: it makes the surface of the bread become more stable," Cheng said, explaining that the laser uses carbon dioxide to change the surface of the material. "You end up with a more stable, porous product than you started with. This material can improve the sensitivity of the sensor and improve the conductivity of other components."

heng said the lasers used were supplied from most processing workshops. "These materials are cheap, and more expensive tools are widely available -- there are hundreds of these lasers at Penn State alone," says co-corresponding author Cheng Zhang, a visiting scholar in Cheng's lab at Zhongmin Jiang University. "With the low cost and widespread availability of materials and tools, this approach can certainly be scaled up for use in clinical Settings."

Since each device uses the same nanocomposite material, the components of the system can work together seamlessly, Cheng said. Each component can also be stretched and bent to adhere to human skin or clothing without losing sensitivity, as the 3D nanocomposite foam is pre-stretched to create a "rumpled" effect.

"Through simple fabrication, the electrical conductivity, mechanical strength and specific surface area of pleated porous graphene /MXenes are improved, providing opportunities for applications in stand-alone stretchable device platforms," Zhang said.

To prove the proof of concept, a research assistant wore a gas sensor under her nose and on her wrist, a nanogenerator on her shoe, and a series of tiny supercapacitors on her shirt. The person exercised vigorously, and the nanogenerator collected the energy generated by their foot movements. This energy is stored by tiny ultracapacitors, which use it to collect data and send it from a gas sensor to a Bluetooth receiver, where scientists can analyze it. Sensors continuously monitor exhaled gas and nitrogen dioxide in the environment.

"The measurements are consistent with those from commercial sensors," Cheng said. He also noted that the system has shown a stable rate of over 50 days in laboratory tests, indicating long-term stability of the system in real-life applications.

Source: Laser Net