Development in Two-Dimensional Nanomaterials for Wearable Health Monitoring Systems
Authors: Lee Eunji , VahidMohammadi Armin , Lee Doohee , Yoon Jaesik , Beidaghi Majid , Yoon Young Soo , Kim Dong-Joo 
Published: February 2020

By virtue of the technology in ubiquitous computing and smart textile, gas sensor with wearability has been developed to play an imperative role in improving future healthcare. [1] The sensor revolution can significantly impact on outpatient care and management of chronical diseases by offering real-time condition monitoring. The combination of many technology is on the verge of producing this dramatic advance, and the significance placed on the development of sensor performance. [2] Recently, two-dimensional (2D) nanostructured materials have been regarded as instrumental sensing materials due to their working ability at low temperature. One attractive approach to enhance performance of 2D materials-based sensor is to hybridize with metal oxide. By grafting two nanostructured materials, sensing performance can be highly advanced by hybridization effects. [3] Another innovative strategy is to adapt newly discovered 2D materials. 2D transition metal carbides and/or carbonitrides (called MXenes) have recently shown excellent properties particularly in energy storage, and water purification applications. [4] Boundless combination of constituent elements and ordered structure in MXenes provides many opportunities to tailor its properties for different applications.
In this study, 2D nanostructured nanomaterials and their hybrids were explored to develop wearable chemical sensor for precise health monitoring systems. Graphene oxide (GO) and molybdenum disulfide (MoS2) were studied to understand the effect of surface dangling bonds on gas sensing properties. To enhance sensing performance, 2D nanomaterials was combined with metal oxides. The gas sensing performance of the GO/TiO2 hybrid was improved by decorating titanium dioxide (TiO2). [5] After photo-reduction, the gas sensing behavior was converted from n-type to p-type with extended long-term stability. Moreover, 2D MXene was introduced as a promising room-temperature sensing material with their intriguing surface chemistry. The capability of titanium carbide (Ti3C2Tx) to sense an array of VOC gases was demonstrated, and its possible sensing mechanism was proposed in terms of the interaction between sensing species and the oxygen terminated surface of MXene. Another MXene material, vanadium carbide (V2CTx), was also investigated. 2D V2CTx gas sensors showed outstanding gas sensing performance including high sensitivity toward non-polar gases such as hydrogen and methane. Transformation of ordered structure and constituent elements of MXenes largely influenced on interaction between analyte and MXenes showing outstanding selectivity and limit of detection to non-polar gases.
References

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Acknowledgement
This research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), grant funded by the Korea Government Ministry of Trade, Industry and Energy (20158520000210), and Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD).