1：Experimental Design and Method Selection:

The study uses finite element analysis (FEA) to model a 1D plasmonic grating on a gold (Au) film over a glass substrate. The design involves horizontal nano-strips with periodic nano-sized gaps (slit-width). TM light illuminates the metallic films from the substrate side at normal incidence.

2：Sample Selection and Data Sources:

The model uses a glass substrate with a refractive index of 1.50 and Au as the sensing element. The wavelength range for the model is from 400 nm to 1000 nm.

3：50 and Au as the sensing element. The wavelength range for the model is from 400 nm to 1000 nm. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: The computational modeling is performed using COMSOL Multiphysics 5.4a (licensed version) with its RF module based on FEA.

4：4a (licensed version) with its RF module based on FEA. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The study involves varying the periodicity (Λ) from 480 nm to 840 nm and the slit width (w) as half of the periodicity. The Au film thickness is kept constant at 50 nm, and the analyte height is 500 nm. Transmission spectra are extracted for different refractive indices (1.00 to 1.10).

5：00 to 10). Data Analysis Methods:

5. Data Analysis Methods: The refractive index sensitivity (RIS) is calculated as the ratio of the shift in resonance wavelength to the shift in refractive index. Near field and far-field analyses are conducted to support the optimized geometrical parameters.