A wearable gas sensor was developed that is an improvement on existing wearable sensors because it uses a self-heating mechanism that enhances sensitivity. It allows for quick recovery and reuse of the device. Other devices of this type require an external heater. In addition, other wearable sensors require an expensive and time-consuming lithography process under cleanroom conditions.
Previous work involved using nanomaterials for sensing because their large surface-to-volume ratio makes them highly sensitive; however, the nanomaterial is not something that can receive a signal, necessitating the need for inter-digitated electrodes, which are like the fingers on a hand.
The researchers used a laser to pattern a highly porous single line of nanomaterial similar to graphene for sensors that detect gas, biomolecules, and in the future, chemicals. In the nonsensing portion of the device platform, the team created a series of serpentine lines coated with silver. When an electrical current is applied to the silver, the gas sensing region locally heats up due to significantly larger electrical resistance, eliminating the need for a separate heater.
The serpentine lines allow the device to stretch, like springs, to adjust to the flexing of the body for wearable sensors.
The nanomaterials used in this work are reduced graphene oxide and molybdenum disulfide or a combination of the two, or a metal oxide composite consisting of a core of zinc oxide and a shell of copper oxide, representing the two classes of widely used gas sensor materials — low-dimensional and metal oxide nanomaterials. Using a CO2 laser, multiple sensors can be made on the platform. The plan is to have tens to a hundred sensors, each selective to a different molecule like an electronic nose, to decode multiple components in a complex mixture.
Applications include a wearable sensor to detect chemical and biological agents that could damage the nerves or lungs, and patient health monitoring including gaseous biomarker detection from the human body and environmental detection of pollutants that can affect the lungs.
The sensor can detect nitrogen dioxide, which is produced by vehicle emissions, and sulfur dioxide, which, together with nitrogen dioxide, causes acid rain. These gases can be an issue in industrial safety.
The researchers’ next step is to create high-density arrays, improve the signal, and make the sensors more selective. This may involve using machine learning to identify the distinct signals of individual molecules on the platform.