Accurate and continuous monitoring of pollutants such as nitrogen oxides (NOx) in high humidity is a difficult challenge for low-cost, extensible gas sensors.
Study: Extensible, moisture-resistant NOx gas sensors based on laser-induced graphene for environmental control and breath analysis. Image credit: Magic mine / Shutterstock.com
A recent article published in Microsystems & Nanoengineering describes the design and implementation of a new, moisture-resistant and wearable NOx-based graphene (LIG) -based NOx gas sensor that has proven successful in controlling and classifying the environment. people with respiratory problems.
Importance of nitrogen oxide (NOx) detection.
Nitrogen oxides (collectively called NOx) produced by combustion processes and oil refineries are important air pollutants that cause bronchitis, asthma, and heart-aggravating disorders.
Nitric oxide (NO), a key biomarker for lung inflammation, is of great relevance for the non-invasive detection and treatment of respiratory disorders such as lung cancer and ventilator-associated pneumonitis. This is because the level of nitric oxide in the exhaled breath of asthma patients exceeds hundreds of parts per billion (ppb), but this amount is less than a few dozen ppb in healthy individuals.
Consequently, it is of the utmost importance to create new, inexpensive and reliable gas sensors to continuously and accurately detect nitrogen oxide (NOx) in human breath.
Graphene-based portable gas sensors for NOx detection
Various technologies have been developed that use nanoparticles such as metal oxides, graphene, carbon nanotubes, and conductive polymers to detect NOx in human breath.
Unlike electrolytic cells, field effect semiconductors, and other conventional gas sensors, graphene-based portable NOx gas sensors have low noise and good mechanical robustness.
Portable electronic devices can collect electrical, biochemical, thermal, physical, and biological information for comprehensive health management. Growing interest in personalized air quality assessment and breath testing has also increased the need for graphene-based portable gas sensors that can detect various harmful chemicals, such as nitrogen oxides (NOx). , accurately and continuously.
Graphene-based gas sensors with unmodified surfaces show little accuracy due to the absence of active sites. To address this problem, newly discovered 3D laser-induced graphene (LIG) can be used because it provides a large number of active sites on the surface for gas-solid interactions.
Relative humidity: an important limitation in the accurate detection of gases
As water particles fill the functional sites on the active surface of the detection nanomaterials, the relative humidity (RH) significantly affects the absorption and equilibrium mechanisms of the target gas, resulting in substantial changes in response in samples. ‘breath with an HR between 50 and 95 percent.
The impact of relative humidity on gas detection can be minimized by the use of coated integrated heating components, hydrophobic self-assembled monolayers (SAMs), or electronic nose algorithms. However, these technologies often increase the sophistication and cost of producing gas sensors.
Therefore, it is crucial to establish a simple method to design and manufacture moisture-resistant NOx gas sensors with a high response rate, rapid response / recovery, and a low detection limit (LOD) to control local air pollution. and analyzing breath samples for disease diagnoses.
A new moisture-resistant LIG-based NOx gas sensor
In this study, the researchers created a new, flexible, moisture-resistant LIG-based NOx gas sensor, interspersing the LIG detection area between a semipermeable polydimethylsiloxane (PDMS) layer and a flexible elastomeric platform.
The flexible, extremely sensitive and selective LIG-based gas sensor consists of a straight LIG detection area and a coil electrode on a smooth elastomeric platform. The LIG detection region has a much narrower width (150 micrometers) than the electrodes to produce substantially stronger resistance and concentrated Joule heating in the detection zone.
The fast, low-cost manufacturing method is also scalable, promising large-scale rapid production for commercial applications in the future.
Key research developments
At room temperature, the prepared gas sensor shows a high response rate, a rapid response / recovery, and an ultra-low detection limit (LOD) for various nitrogen oxides (NOx). By adjusting laser processing parameters such as laser intensity, image frequency, and blur distance, the direct laser writing method can produce LIG detection zones with different morphologies.
This unique water-resistant LIG-based gas sensor can detect outdoor air quality at different times of the day by combining a high elasticity of 30 percent and a moisture-resistant capability against a relative humidity of 90 percent. one hundred. In addition, you can quickly evaluate clinical samples of breath to properly distinguish between patients with respiratory diseases and healthy humans.
Reference
Yang, L. et al. (2022). Extensible, moisture-resistant NOx gas sensors based on laser-induced graphene for environmental control and breath analysis. Microsystems and nanoengineering. Available at: https://doi.org/10.1038/s41378-022-00414-x
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