1：Experimental Design and Method Selection:

The study uses a lossy mode resonance (LMR) based optical fiber sensor with a SnO2 sputtered coating as the LMR-supporting layer and a PEI/GO multilayer as the sensitive coating. Dip-assisted layer-by-layer (LbL) assembly is employed for thin film deposition due to its cost-effectiveness, simplicity, and coating uniformity.

2：Sample Selection and Data Sources:

A multimode optical fiber (FT200EMT from Thorlabs, Inc.) with a 200 μm core is used. Materials include polyethylenimine (PEI) solution from Sigma Aldrich and graphene oxide (GO) powder from Graphenea S.A.

3：List of Experimental Equipment and Materials:

Equipment includes a sputter coater (K675XD from Quantum Technologies), cleaver (NorthLab ProCleave LD II), fusion splicer (Fitel S178A), white light source (HL2000 from Oceanoptics Inc.), spectrometer (Oceanoptics USB2000), environmental chamber (Binder KMF 115), XPS system (Thermo Scientific K-Alpha), FTIR spectrometer (Nicolet stepscan with diamond ATR), SEM (FEI NanoSEM 450 FEG), and stylus profiler (DektakXT from Bruker). Materials include PEI, GO, SnO2, KOH, HCl, NaOH, and deionized water.

4：Experimental Procedures and Operational Workflow:

The fiber cladding is thermally removed, and the core is cleaned. SnO2 is sputtered onto the core. A 2 cm fiber fragment is cleaved and spliced to pigtails. PEI and GO solutions are prepared and used for LbL deposition with 5 bilayers (5 minutes immersion each, with rinsing and drying). The sensor is characterized in an environmental chamber with RH varied from 20% to 90% at 20°C, and dynamic responses are measured for breathing monitoring.

5：Data Analysis Methods:

Spectra are collected using a spectrometer, and a MatLab routine is used to fit polynomial curves to LMR peaks to determine wavelength shifts. Sensitivity, hysteresis, response times, and other parameters are calculated from the data.