Wearable sensors have garnered tremendous interest for smart sensing applications such as electronics and environmental monitoring. High performance sensors with adaptable and wearable platform are anticipated to play an important role in future medical diagnostics and physiological monitoring. For example, the level of exhaled ammonia can be an important index for viral and bacterial infections in lung diseases or in renal diseases, and the use of easy accessible breath testing device will be beneficial to early detection of disease by continuously checking human’s breath. To actualize wearable electronic nose sensors, functional materials that measure amounts of gases should be built on fabrics/fibers. For such purpose, graphene oxide (GO) can be an excellent candidate due to its remarkable physicochemical properties including high specific surface area and excellent electrical property. With GO, high operation temperature is not necessary which is required with metal oxide gas sensor. In order to apply GO to wearable sensors, GO should be integrated into fabrics such as nylon and polyester for flexible and room temperature operation. However, integration of the electrode and sensing materials on fabric demands greater challenge due to woven and non-organized fabric structure. Technically, coating methods such as vapor phase deposition are limited to build nanostructure on real fabrics, and fabricating of micro-size electrode on uneven surface requires delicate technique.

In this study, we successfully fabricated interdigitate electrode on nylon/polyester/cotton fabrics and demonstrated ammonia gas sensing with GO at room temperature. There has been much research to use alternative flexible substrates such as paper and polymer, however, practical fabrics were rarely investigated. Different weave pattern of nylon and polyester fabrics were used as representative synthetic textiles, and cotton was represented a natural fiber. Thin PVC film was pre-coated on the woven fabrics prior to sputtering electrode because of electrode connection. Each electrode bridge was well sputtered on flat coated fabrics without disconnection, since thin PVC film laminates the fabrics as mitigating coarse surface of woven fabric. Next, a facile solution method was explored to construct GO on fabrics which is compared to commonly investigated vapor phase deposition. A 10g/L GO solution was ultrasonicated to get uniformly stirred solution, and a splash of GO was dropped on the electrode of sensor platform. The resistance of dried GO film coated on fabrics was measured with 100ppm ammonia bubbling, and the gas response was calculated using the ratio of the resistance measured in detecting gas to that measured in air. The ratio of the resistance was found to be around 0.4. The difference of surface roughness depending on existence of PVC film coated on the sample was investigated by optic microscope to relate the influence of the structure on the sensing performance. The morphologies of GO film on fabrics were analyzed with SEM and XRD, and detailed discussion on the mechanism of GO to ammonia will be given.

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