Fig. 1. Raman spectrum of the WS2 layers on the SPR sensor structure.

Fig. 2. (a) WS2 surface morphology image of the SPR sensor. The WS2 cross section SEM images after different numbers of times of repeated post-coating: (b) one; (c) two; (d) three; (e) four; (f) five.

Fig. 3. Experimental setup for RI sensing measurement.

Fig. 4. Reflectance spectra of the WS2-SPR sensors corresponding to different post-coating times: (a) Without coating; (b) one; (c) two; (d) three; (e) four; (f) five. The refractive index of the sensing analyte changes from 1.333 to 1.360.

Fig. 5. Experimental variation of shift in the resonance wavelength with refractive index under different times of WS2 nanosheet post-coating: (a) Without coating; (b) one; (c) two; (d) three; (e) four; (f) five.

Fig. 6. (a) Sensitivity and (b) figure of merit comparison for different number of times of WS2 nanosheets coatings.

Fig. 7. (a) Experimental variation of shift in the resonance wavelength with surrounding refractive index ranging from 1.333 to 1.40. (b) Evanescent electric field distribution at the resonance wavelength within the prism/gold film (50 nm)/analyte (n=1.36) structure.