Biodegradable Isopropyl Alcohol-Modified Cellulose Paper Sensor for Rapid and Real-Time Monitoring of Breathing Profiles

The demand for flexible, biocompatible, and sustainable humidity sensors is rising in health diagnostics and wearable electronics. Cellulose, as a biodegradable and humidity sensitive material, offers a promising platform for low-cost, disposable sensing. Here, we report a simple isopropyl alcohol (IPA)-modified cellulose-paper-based humidity sensor with enhanced surface properties for efficient proton conduction. IPA treatment reconfigures the cellulose surface, improving its hydrophilicity and enabling faster and more sensitive moisture adsorption and desorption. The resulting sensor shows a sharp increase in current above 55% relative humidity (RH), with a linear and repeatable response across 60–100% RH. It achieves a rapid response and recovery time of ∼1.45 s, making it suitable for real-time breath monitoring. Integrated into a wearable oxygen mask, the sensor accurately tracks normal and abrupt breathing patterns in multiple subjects, demonstrating potential in respiratory diagnostics, such as sleep apnea or COPD detection. This work presents a scalable route to develop eco-friendly, disposable, and wearable sensors, emphasizing sustainable materials for next-generation biomedical monitoring technologies.