Highly sensitive, flexible and transparent TiO2/nanocellulose humidity sensor for respiration and skin monitoring

Because of its biodegradability, biocompatibility, strong hydrophilicity, and high specific surface area, nanocellulose has been considered as a potential material for flexible humidity sensors. Herein, we developed a TiO2/ CNC humidity sensor with good flexibility based on the nanocellulose (CNC) prepared by the enzymatic method. Nano TiO2 with a positive charge was adsorbed on the surface of CNC with a negative charge, and conductive fibers were obtained by an electrostatic self-assembly process. The TiO2/CNC composite exhibits high optical transmittance (84.5% at 600 nm), flexibility (the tensile elongation reaches 57.82%), and robust mechanical property (the tensile strength reaches 44.66 MPa). The obtained TiO2/CNC humidity sensor achieved high humidity response (R0/R = 450.9), rapid response/recovery speed (22/13 s), folding durability (20 times), and long-term stability (40 days). TiO2/CNC had outstanding performance in actual respiratory rate detection, and the assembled TiO2/CNC skin moisture detector with flexibility and transparency could monitor human body moisture in real-time, showing its potential as a smart wearable device.

Automated summary

Due to its biodegradability, biocompatibility, hydrophilicity, and surface area, nanocellulose has potential for use in flexible humidity sensors. In this study, a TiO2/CNC humidity sensor was developed using nanocellulose prepared enzymatically. TiO2 nanoparticles were adsorbed onto the CNC surface, creating conductive fibers through electrostatic self-assembly. The TiO2/CNC composite exhibited high transparency, flexibility, and mechanical strength. The humidity sensor showed high response, rapid speed, durability, and stability. The TiO2/CNC sensor also demonstrated excellent performance in real-time monitoring of human body moisture.