MOF-on-MOF layer-coated optical fiber sensor for water vapor sensing

We present a simple optical fiber sensor with a MOF-on-MOF (Co-ZIF-90-on-ZIF-8 in this work) coating for water vapor sensing and detection, with a sensing mechanism based on the refractive index variation as a function of analyte adsorption within the MOF layer. A seeding layer approach was employed to grow the MOF-on-MOF layers with high quality for optical sensing application. The resulting sensor exhibits stable sensitivity to water vapors with excellent reversibility of vapor adsorption and desorption. The evaluated adsorption and desorption times of water vapor are approximately 48 seconds and 29 seconds, respectively. The demonstrated bi-layer MOF-based optical sensor provides the potential to further develop easy-to-fabricate sensors as well as multiplexed and distributed sensors in an inexpensive and reproducible way.