MXene and Conducting Polymer Composites for Wearable Mask Sensors
Authors: Wu Guodong , Pakravan Kiandokht , Kim Wonhyeong , Cha Yoolim , Beidaghi Majid , Kim Dong-Joo 
Published: December 2024

Significant efforts have been dedicated to advancing wearable electronics, ranging from life-supporting gear for soldiers to trendy accessories like smartwatches. Miniature gas sensors integrated into wearable devices offer real-time atmospheric information, safeguarding individuals from potential health condition monitoring and early disease detection. For example, recent studies have focused on detecting COVID-19 through breath analysis, utilizing over 500 compounds in exhaled breath as biomarkers for disease and metabolic assessment. Of particular interest is CO2, a key greenhouse gas crucial for monitoring indoor air quality and respiratory health. Excessive indoor CO2 levels, primarily from human exhalation, elevate the risk of COVID-19 transmission via aerosols. Another example of a considerable gas species in exhaled breath can be ethanol, which could cause adverse effects such as nausea, vomiting, skin allergies, low blood pressure, low blood sugar, and Parkinson's disease, seriously threatening human health and safety driving. Various techniques, including optical spectroscopy and gas chromatography, have been employed for gas detection, but they often suffer from drawbacks like bulkiness and high cost. Therefore, there is a strong need for developing detection devices that are affordable, portable, and wearable. Conducting polymers (CPs) show promise in constructing flexible gas sensors, but their limited response to diverse gases necessitates exploring hybridization with other nanomaterials to enhance sensing capabilities.
In this study, two kinds of conducting polymers, including polyaniline (PANI) and polypyrrole (Ppy) were synthesized in a composite form with Ti3C2Tx MXene and deposited into polypropylene fiber-based disposable masks. The PANI-MXene composite gas sensor displayed a wide detection range, reliable reproducibility, long-term stability, and excellent flexibility and selectivity, a remarkable response (15.2%) towards 500 ppm CO2 gas, which is 6.5 times higher than pristine Ti3C2Tx and 2.4 times higher than pristine PANI. When Ppy is hybridized with Ti3C2Tx, the as-fabricated composites exhibited a rapid response/recovery speed, a good sensing response of 76.3 % toward 400 ppm ethanol, and an admirable theoretical limit of detection of 2.21 ppm. The outstanding sensing characteristics of the composite sensor are attributed to the abundant functional groups (e.g., amino groups in conducting polymers, terminal groups in Ti3C2Tx) and the formation of the Schottky junction between Ti3C2Tx and conducting polymers. Furthermore, a wearable wireless Bluetooth sensing device was developed for human breath monitoring, showcasing the potential of these MXene-CP composite sensors for respiratory disease diagnosis [1, 2]. The proposed gas sensing mechanism of the CP-based composites is also discussed in detail.
References
[1] Wu, G., Du H, Pakravan, K., Kim, W., Cha, Y. L., Chiang, S.-T., Beidaghi, M., Zhang, X., Kim, S. H., Pan, X., Kim, D.-J. (2023). Polyaniline/Ti3C2Tx functionalized mask sensors for monitoring of CO2 and human respiration rate. Chemical Engineering Journal, 475, 146228.
[2] Wu, G., Du H, Pakravan, K., Kim, W., Cha, Y. L., Beidaghi, M., Zhang, X., Pan, X., Kim, D.-J. (2024). Wearable room-temperature ethanol sensor based on Ti3C2Tx/Polypyrrole functionalized face mask for drunk driving monitoring. Carbon, 216, 118565.