Ultrasensitive humidity detection using metal-organic framework-coated microsensors

Area of Science:

• Materials Science
• Chemical Engineering
• Sensor Technology

Background:

• Metal-organic frameworks (MOFs) offer tunable porosity for various applications.
• Surface Acoustic Wave (SAW) sensors are sensitive to mass changes on their surface.
• Detecting water vapor requires sensors with wide dynamic range and stability.

Purpose of the Study:

• To demonstrate the use of MOF thin films for water vapor detection using SAW sensors.
• To evaluate the sensitivity and regeneration capabilities of MOF-functionalized SAW sensors.
• To investigate the water adsorption behavior within the MOF structure.

Main Methods:

• Fabrication of MOF (Cu-BTC) thin films on quartz SAW sensor substrates using automated layer-by-layer deposition.
• Testing sensor response across a wide range of water vapor concentrations (0.28–14,800 ppmv).
• Covalent bonding of MOF layers to enable high-temperature regeneration (>100 °C).
• Computer simulation of H2O uptake and adsorption isotherms within the MOF structure.

Main Results:

• MOF-functionalized SAW sensors achieved a wide detection range (3–14,800 ppmv with automated deposition; 0.28–14,800 ppmv with manual deposition).
• The sensors demonstrated high sensitivity, exceeding many commercial alternatives.
• Covalently bonded MOF layers allowed for effective sensor regeneration at temperatures above 100 °C without decomposition.
• Experimental and simulation results for water uptake showed consistency, indicating efficient H2O adsorption by Cu-BTC.

Conclusions:

• MOF functionalization of SAW devices provides a highly sensitive and reusable platform for water vapor detection.
• This approach demonstrates the potential of MOFs to enhance compact sensing technologies.
• MOF-based SAW sensors show promise for competing with state-of-the-art sensing devices.