Silk fibroin based transparent and wearable humidity sensor for ultra-sensitive respiration monitoring

•A transparent and ultra-high sensitive respiratory monitoring sensor based on silk fibroin was developed.•A cost-effective and eco-friendly technology for Ag NWs patterning at high resolution was proposed.•The sensors can distinguish different intensities and rates of respiration with a rapid response up to 4 Hz. Recently, the development of biocompatible and transparent devices for high sensitivity respiration monitoring has become a hot topic. Herein, a capacitive-type humidity sensor based on the silk fibroin dielectric sensing film was proposed. Both the breathing rates and intensities were recognized through the capacitance changes induced by vapor penetration. A low-cost and facile patterning method was proposed to prepare the Ag nanowires interdigitated electrodes (IDEs). The sensors showed rapid responses toward environmental humidity variations and different breathing conditions, covered the breathing rate up to 4 Hz. The sensor had a transmittance of above 85%. Mechanical and electrical stabilities of the sensor were confirmed through a bending test. A portable kit integrated with conventional electronics was attempted, demonstrating the practical use is on the way.