In Situ Determination of Chloride Ions Using a Novel Double-Layer Membrane Optical Fiber Sensor Modified with the UiO-66-NH2/Lucigenin Complex

Chloride quantification is crucial for environmental monitoring, marine research, and the durability assessment of geotechnical infrastructures, yet accurate measurement in complex aqueous and soil matrices remains challenging. Optical fiber sensors offer distinct advantages, including resistance to electromagnetic interference, high sensitivity and low cost. Unfortunately, existing fiber-optic chloride sensors are often limited by insufficient sensitivity, poor anti-ion interference, inadequate portability, and an inability to perform long-term in situ monitoring. Herein, a novel fluorescent optical fiber chloride sensor based on UiO-66-NH2/lucigenin composite is fabricated, in which the mixture formed lucigenin encapsulated with UiO-66-NH2 is immobilized within a dual-layer membrane composed of an inner cellulose acetate (CA) matrix and an outer polyvinyl alcohol (PVA) membrane. The chloride-responsive fluorescent probe operates on the principle of fluorescence quenching. The dual-layer sensitive membrane is engineered to significantly enhance sensitivity, linearity, and stability for long-term monitoring. Furthermore, the portable device eliminates the constraints of bulky optical systems and mitigates instability caused by photobleaching, enabling reliable in situ chloride detection in water, soil, and geotechnical environments. Experimental results confirm the superior analytical performance of the sensor across various soil and aquatic media. This work represents a notable advancement in the field of fluorescent optical fiber sensors and holds substantial promise for practical applications.