In the past few years, the rapid growth of the information age has captured global attention, particularly regarding the Internet of Things (IoT), artificial intelligence (AI), big data, and cloud computing. Among these technological advancements, smart gas sensors have emerged as a significant interface for human-machine interaction (HMI) and a crucial tool for interacting with the external environment.
When using a gas sensor as an HMI interface, it is crucial for it to be wearable and conform to the skin in order to effectively sense various physiological signals from the human body and the surrounding environment. However, conventional gas sensors are typically fabricated using rigid materials such as glass, ceramic tubes, silicon, and electrodes. These materials lack the necessary flexibility and mechanical compliance to accommodate human movement. As a result, traditional rigid gas sensors have limited bending capabilities and gas permeability, which restrict human activities and result in discomfort when worn.
Moreover, traditional gas sensors often require high-temperature operation, making it challenging to fabricate wearable gas sensing systems. This limitation also increases the potential risk of explosion or fire when detecting flammable and explosive gases. To address these issues, there is a need for innovative approaches that offer improved flexibility, mechanical compliance, and safety in gas sensor design for wearable applications.
Recently reported wearable gas sensors provide an effective solution to the above challenges. With the acceleration of industrialization and urbanization, harmful gas emissions pose a major threat to human health. For example, excessive exposure to ammonia can cause irreversible and severe irritation to respiratory organs and eyes, long-term exposure to air containing formaldehyde can lead to decreased lung function and chronic pneumonia, and long-term exposure to low concentrations of nitrogen oxides can induce Chronic pharyngitis and bronchitis.
Therefore, the immediate detection of harmful gases in the surrounding environment using portable and wearable gas sensors has become increasingly critical in everyday life. Furthermore, certain gases can serve as biomarkers for specific diseases, enabling real-time monitoring, diagnosis, and treatment of human health conditions. This highlights the importance of developing gas sensors that are convenient, easily wearable, and capable of providing valuable insights into human well-being.
Wearable gas sensors find applications in various fields such as environmental monitoring, healthcare, smart homes, industrial safety, food safety, and public safety, depending on the specific gas being detected and the intended application scenario. These sensors are designed to be compact in size and can be comfortably attached to the human skin. They possess the ability to adapt and deform with human motion without compromising the sensor's performance and response capabilities.
As a result, the selection and design of flexible substrates and sensitive materials have become crucial in enhancing the room temperature sensing performance and mechanical flexibility of gas sensors. Innovative options such as polymer and textile substrates have emerged, offering not only bendable and stretchable properties but also lightweight and cost-effective alternatives to traditional rigid substrates. These advancements pave the way for improved gas sensor technologies with enhanced flexibility and performance.
In order to achieve real-time detection of human physiological signals and monitor potential environmental threats, flexible sensing materials such as ionic liquids, polymers, carbon-based nanomaterials, and two-dimensional semiconductor materials offer promising solutions. These materials exhibit excellent flexibility and high sensitivity at room temperature, providing distinct advantages over other materials. Moreover, wearable gas sensors also exhibit lower power consumption compared to traditional gas sensors, making them more energy-efficient for prolonged usage.
A recent publication titled "Room Temperature Wearable Gas Sensors for Fabrication and Applications" by Professor Liu Fangmeng's research team from the School of Electronic Science and Engineering at Jilin University, as reported by Memes Consulting, offers a comprehensive review. This review focuses on materials exhibiting excellent gas sensing properties and their fabrication techniques. Additionally, the article delves into various applications and future possibilities for wearable gas sensors operating at room temperature. The findings provide valuable insights into the advancements and potential of this emerging field.
Sensing mechanism of a wearable gas sensor operating at room temperature
Currently, there are four primary types of gas sensors: optical gas sensors, mechanical gas sensors, electromagnetic gas sensors, and electrical/electrochemical gas sensors. Each type generates a distinct signal. Among these, electrical/electrochemical gas sensors operate by monitoring the alteration of electrical characteristics when gas molecules react with the sensor, allowing for the detection of target gas concentration. This paper elucidates the sensing mechanism through models such as the oxygen adsorption model, direct adsorption model, proton transfer model, and ion conduction model.
Flexible sensitive material
The flexibility of gas sensors has emerged as a critical factor limiting the widespread application of wearable smart devices. Consequently, extensive research has focused on enhancing the mechanical flexibility of both sensitive materials and substrates. This article provides a brief overview of flexible gas-sensing materials, such as ionic liquids, polymers, carbon-based nanomaterials, and transition metal compounds. These materials hold promising potential for replacing conventional rigid materials in the development of smart devices. By incorporating flexible gas-sensing materials, wearable smart devices can achieve improved flexibility and adaptability, enabling seamless integration into various applications.
Wide application of wearable gas sensors
In comparison to conventional rigid gas sensors, wearable gas sensors offer greater flexibility in terms of assembly options and are not constrained to fixed locations. These wearable sensors can seamlessly adhere to human skin or be integrated into clothing as electronic fabrics, allowing them to bend and flex with human motion while maintaining their gas sensing performance. Importantly, wearable gas sensors enable real-time detection of surrounding environmental conditions and physiological signals of the human body.
By leveraging technologies such as the Internet of Things (IoT) or deep learning, wearable gas sensors can issue timely warnings when harmful gas concentrations or respiratory markers exceed safety thresholds. Their comfort and portability make them suitable for continuous, all-day wear, enabling real-time monitoring. As a result, wearable gas sensors have proven valuable in a range of applications including environmental monitoring, healthcare, smart homes, food safety, and even public safety, where real-time monitoring and immediate alerts are essential.
Future Research Prospects
Despite the promising opportunities presented by wearable gas sensors, several challenges need to be addressed before they can be widely applied in practical settings. Firstly, sensitive materials utilized in these sensors often exhibit lower response levels and longer response/recovery times compared to materials operating at higher temperatures. Consequently, there is an urgent need to investigate doping techniques and material structures to enhance the sensing performance of existing materials at room temperature.
Moreover, room temperature sensing materials like Ti3C2Tx and PANI suffer from stability issues and are prone to oxidation, limiting their broader application in wearable gas sensors. Finding solutions to improve the stability of these materials is essential.
Secondly, in terms of device fabrication, it is crucial to ensure the stability of gas sensing performance under significant mechanical deformation, achieve miniaturization and integration, and meet the requirements of wearable smart devices.
Lastly, integrating gas sensing applications with emerging technologies like big data, artificial intelligence, and machine learning holds great promise. Such integration can accelerate the digitization, intelligence, and seamless integration of wearable gas sensors.
Addressing these challenges will pave the way for practical applications of wearable gas sensors, driving advancements in the field and enabling their widespread use in diverse industries.
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