Flexible humidity sensor with high responsiveness based on interlayer synergistic modification of MXene for physiological detection and soil monitoring

With the rapid advancements in healthcare, human-computer interaction, and electronic devices, the demand for high-performance wearable flexible sensors has grown significantly. Among emerging materials, MXene stands out for its abundant hydrophilic functional groups, large reactive surface area, and exceptional electrical conductivity, making it a promising candidate for flexible humidity sensors. However, MXene also has notable drawbacks, including rapid oxidative degradation, severe layer stacking, and limited mechanical strength. These limitations make it difficult for MXene-based humidity sensors to simultaneously achieve high response, outstanding sensitivity, and robust flexibility. A flexible humidity sensor based on poly(indole-6-amine)/MXene/ carboxymethyl cellulose (P6AIn/MXene/CMC) composite material with high-performance was proposed in this work. The positively charged P6AIn self-assembles onto MXene layers and CMC surfaces, enhancing interlayer spacing to create nanoscale channels for rapid water molecules adsorption and desorption. This arrangement also forms a conductive network between MXene layers, significantly improving electron transfer efficiency. As a result, the sensor demonstrates excellent humidity-sensing performance, including remarkable linearity (R2 = 0.99928), ultra-high response (17340), and rapid response time (4 s) across a relative humidity range of 11 %-98 %. Additionally, the structural intercalation and surface modification introduced by P6AIn and CMC confer the sensor with superior mechanical strength and environmental stability. Even under prolonged operation, it maintains consistent performance, making it well-suited for wearable humidity monitoring in diverse environments. Furthermore, the P6AIn/MXene/CMC sensor enables real-time monitoring and identification of respiratory states, finger humidity, and soil humidity. This work not only provides a novel solution for developing highperformance wearable humidity sensors but also highlights significant potential for applications in intelligent sensing, healthcare, and automated irrigation.