1：Experimental Design and Method Selection:

The study involves the fabrication of a polymer optical fiber (POF) sensor modified with cladding treatment and a bi-layer zinc oxide/silver (ZnO/Ag) nanostructure coating. Three different ZnO nanostructure shapes (nanoparticles, horizontally and vertically oriented nanorods) are used as an external layer. A broad spectrum light source from the visible (Vis) to the near infrared (NIR) region is employed to achieve optimum sensitivity.

2：Sample Selection and Data Sources:

Multimode POF with a diameter of 486 mm and 14 mm for core and cladding, respectively, was purchased from Jiangxi Daishing POF company. The cladding material is fluorinated polymethyl methacrylate (PMMA) with a refractive index of 1.402, and the core is made of PMMA with a refractive index of 1.

3：402, and the core is made of PMMA with a refractive index of List of Experimental Equipment and Materials:

492. 3. List of Experimental Equipment and Materials: Materials used include acetone, methanol, silver nitrate, ammonia solution, zinc nitrate hexahydrate, sodium hydroxide, tin(II) chloride, palladium(II) chloride, boron hydride dimethylamine, hydrochloric acid, zinc acetate dihydrate, triethylamine, isopropyl alcohol, hexamethylenetetramine, and sodium chloride. Equipment includes a field emission scanning electron microscope (FESEM), AFM, XRD, photoluminescence spectrometer, UV-VIS/NIR spectrophotometers, Zetasizer NanoZS instrument, Thorlabs' Stabilized Light Sources, and an optical spectrum analyzer (OSA).

4：Experimental Procedures and Operational Workflow:

The POF sensor is fabricated through cladding modification, coating with Ag nanoparticles as an inner layer, and coating with different ZnO nanostructures as an outer layer. The sensor's performance is tested by immersing it in saline solutions of different concentrations and measuring the light transmission characteristics.

5：Data Analysis Methods:

The sensitivity of the sensor is evaluated based on wavelength and intensity changes in the transmitted light. The structural and optical characteristics of the ZnO nanostructures are analyzed using FESEM, AFM, XRD, and photoluminescence spectroscopy.