Environment-friendly Hanji cellulose paper-based humidity sensor for multifunctional applications

Abstract Recent advancements in sensor technology have led to the development of humidity sensors with applications in multiple fields such as agriculture, medical, food storage, and processing industries. Recently, the focus in humidity sensor research has moved towards creating sensors that are not only flexible and low-cost but also harmless to humans and eco-friendly. However, it requires clean rooms, nonbiodegradable substrates like silicon elastomers, and intricately synthetic highly toxic metallic sensing materials (based on Ti, Ru, Ni, etc.). These factors result in high costs, negative skin and environmental effects, and a substantial increase in the need for landfill space. Here, we propose Hanji cellulose paper-based humidity sensor with having rich hydrophilic and porous surface. Our Hanji humidity sensor has stable humidity sensing response close to 106 and demonstrates a linearity of R2 = 0.9912 across a relative humidity range from 7.6 to 91.8% by using just 0.3 V. In addition to its performance, Hanji humidity sensor is environment-friendly, cost-effective, naturally decomposable, and flexible, requiring only two simple fabrication steps. It shows potential applications like fingertip moisture detection and breath intensity monitoring. Further engineering and surface modifications will not only enhance its performance but also expand its potential for additional applications in the field of humidity sensing.