Flexible and Cost-Effective Graphene-Based Sensor on Paper Substrate Using Pencil IDEs for Multifunctional Applications in Plant and Human Health Monitoring

The growing importance of flexible sensors is driven by their adaptability, lightweight design, and ability to integrate seamlessly into various surfaces, making them indispensable across numerous applications. Among these, paper-based sensors have emerged as a potential candidate due to their sustainability, cost-effectiveness, and ease of fabrication. In this work, we have introduced a low-cost, flexible humidity sensor constructed on a paper substrate, with interdigitated electrodes drawn using pencils. The simplicity of the pencil-drawing technique, combined with the eco-friendly paper substrate, makes this sensor a practical alternative to conventional sensors. The sensor utilizes graphene oxide as the sensing material, providing high sensitivity to moisture. This enables various applications, including soil moisture monitoring, plant drought monitoring, human breath analysis, human skin moisture monitoring, and proximity sensing. The importance of this work is the sensor’s ability to precisely monitor soil moisture and detect plant water stress, addressing critical needs in precision agriculture monitoring. This shows the potential of the fabricated sensor in the accurate monitoring of soil and plant hydration levels, which is essential for optimizing water management and ensuring sustainable agricultural practices. The sensor’s rapid response and recovery times, minimal hysteresis, and long-term stability make it highly effective for soil moisture-level monitoring. Its ability to noninvasively monitor plant transpiration also enables the reliable detection of drought stress, offering valuable data for optimizing irrigation and maintaining plant health. Furthermore, the sensor’s versatility is highlighted through its effectiveness in human breath monitoring, skin moisture monitoring, proximity sensing, and smart diapers, broadening its potential applications in healthcare diagnostics and touchless interfaces. This study highlights the potential of paper-based, pencil-drawn sensors as a sustainable, low-cost solution for various environmental, agricultural, and physiological monitoring applications, showcasing their practicality for real-world use.