MXene-Based Fiber-Optic Humidity Sensor for Fast Human Breath Monitoring

Breath is one of the most important physiological features of human life. In particular, it is significant to monitor the physical characteristics of breath, such as breath frequency and tidal volume. Breath sensors play an important role in the field of human health monitoring. However, an electronic breath sensor is not stable or even safe when the patient is in a Magnetic Resonance Imaging (MRI) system or during any oncology treatment that requires radiation and other high electric/magnetic fields. Fiber-optic-based sensors have attracted a considerable amount of attention from researchers since they are immune to electromagnetic interference. Here, we propose and demonstrate a fiber-optic-based relative-humidity (RH)-sensing strategy by depositing Ti3C2Tx nanosheets onto an etched single-mode fiber (ESMF). The humidity sensor function is realized by modulating the transmitted light in the ESMF using the excellent hydrophilic properties of Ti3C2Tx. Experiments show that the coated Ti3C2Tx nanosheets can effectively modulate the transmitted light in the ESMF in the relative humidity range of 30~80% RH. The sensor’s fast response time of 0.176 s and recovery time of 0.521 s allow it to be suitable for real-time human breath monitoring. The effective recognition of different breath rhythms, including fast, normal, deep, and strong breathing patterns, has been realized. This work demonstrates an all-optical Ti3C2Tx-based sensing platform that combines Ti3C2Tx with an optical fiber for humidity sensing for the first time, which has great promise for breath monitoring and presents novel options for gas-monitoring applications in the biomedical and chemical fields.