An eco-friendly, ultrahigh-performance impedance humidity sensor using edible soy sauce

Humidity sensors based on biomaterials have gained significant attention due to their eco-friendliness, sustainability, and cost-effectiveness, offering solutions to reduce environmental pollution while meeting manufacturing demands. Among various biomaterials, food-derived substances, such as soy sauce (a traditional and widely used condiment in Chinese cuisine) are particularly promising owing to their unique properties and accessibility. In this work, we developed a high-performance sensor utilizing soy sauce, which is rich in hydrophilic functional groups that enhance humidity sensitivity. The sensor's performance was systematically evaluated over a wide range of relative humidity (RH) levels at room temperature. The results demonstrate exceptional humidity sensing properties, including a broad detection range (0 %–97 % RH), high response (1.1 × 10 6 ), rapid response time (3.4 s), low hysteresis (∼4.3 % RH), and good repeatability. Additionally, thanks to its outstanding humidity sensing, the sensor successfully monitored real-time human respiratory patterns and enabled human skin non-contact detection, demonstrating its potential for multipurpose applications. Furthermore, through detailed analysis, the underlying humidity sensing mechanism for the soy sauce sensor was elucidated with the complex impedance spectroscopy and the Bode diagram. This study not only confirms soy sauce as a promising biomaterial for humidity sensing but also provides a valuable reference for the development and exploration of biomaterials in sensing technologies. • A novel high-performance humidity sensor based on soy sauce is proposed. • The sensor could detection broad range from 0 % to 97 % RH environment. • In 97 % RH environment, the sensor exhibited an ultra-high response of 1.1 × 10 6 and a rapid response time (3.4 s). • This sensor could be utilized for real-time monitoring of human respiratory patterns and contactless detection of human skin characteristics.