Development of a High-Sensitivity Humidity Sensor Using Fiber Bragg Grating Coated with LiCl@UIO-66-Doped Hydrogel

Area of Science:

• Materials Science
• Optical Sensing
• Nanotechnology

Background:

• Humidity monitoring is crucial but challenging for compact, sensitive, and stable sensors.
• Existing electromagnetic interference (EMI)-immune sensors often lack high sensitivity or robust stability.

Purpose of the Study:

• To develop a novel fiber Bragg grating (FBG) humidity sensor with enhanced performance.
• To investigate the use of LiCl@UIO-66 microfillers within a poly(N-isopropylacrylamide) (PNIPAM) hydrogel matrix for humidity sensing.

Main Methods:

• Fabrication of FBG sensors incorporating LiCl@UIO-66 microfillers in a PNIPAM hydrogel.
• Structural characterization using XRD, SEM, EDS, and FTIR spectroscopy.
• Performance evaluation through systematic variation of coating time, humidity cycling, and response time tests.

Main Results:

• The LiCl@UIO-66 composite demonstrated strong interfacial interactions with water.
• Optimal coating time of 4 h provided significant wavelength shift with favorable kinetics.
• Sensitivities reached 10.6 pm/%RH, with response times (t90) around 14 minutes.
• The sensor exhibited good long-term stability and reversibility during humidity cycling.

Conclusions:

• The synergistic combination of hydrogel, MOF, and salt enables high sensitivity, rapid response, and practical stability in optical humidity sensing.
• This approach offers a scalable and effective method for developing high-performance humidity sensors.