Interferometric Optical Fiber Sensor with a Polyoxometalate-Doped Xerogel for the Detection of Ammonia and VOCs

This study presents the development and evaluation of an interferometric optical fiber sensor (I-OFS) based on a Single Mode Fiber-No Core Fiber-Single Mode Fiber (SMF-NCF-SMF) structure and functionalized with a silica xerogel doped with a titanium (IV)-containing polyoxomolybdate (GeMoTi). The sensor behavior was tested under saturated atmospheres of ammonia, water, and various volatile organic compounds (VOCs), including methylamine, ethanol, acetone, and toluene. The response was characterized in terms of wavelength shifts, which are highlightable for ammonia and methylamine due to their strong chemical interactions with the doped xerogel. The response and recovery times were evaluated for each analyte, pointing out ammonia as the compound with the fastest response time and most stable detection performance, while methylamine exhibited longer recovery due to stronger binding. Calibrations with ammonia concentrations from 56 to 313 ppmm demonstrated linearity (R² = 0.98), low hysteresis (6%) and repeatability. These results support the hypothesis of using GeMoTi-doped xerogels to enhance the response of I-OFSs toward ammonia and related amines.