Fig. 1. (a) Schematic diagram of the proposed PC-SPR sensor. Simulated reflectance spectra of the sensor with (b) different bilayers of TiO₂/SiO₂, (c) different d_Au at 30 nm Si layer, and (d) different d_Si at 20 nm Au layer. The ambient RI is 1.33 for the simulations. (e) Performance of the sensor with different d_Si and d_Au. (f) Linear fitting of the resonant wavelength of the optimized PC-SPR device versus ambient refractive index of 1.31–1.37.

Fig. 2. (a) SEM image of the cross-sectional PC-Au on a glass substrate and (b) the corresponding EDS spectrum. (c) SEM image of the cross-sectional glass substrate and (d) the corresponding EDS spectrum.

Fig. 3. (a) Reflectance spectra of the PC-SPR sensors for the liquid RI changing from 1.31 to 1.37, (b) linear fitting of the resonant wavelength versus ambient refractive index, (c) reflectance spectra of the 50 nm Au-SPR sensor with the RI ranging from 1.31 to 1.37, and (d) polynomial and linear fitting of the resonant wavelength versus ambient RI.

Fig. 4. Comparison of the Au-SPR and PC-SPR sensors in terms of (a) sensitivity, (b) FWHM, (c) FOM, and (d) average FOM enhancement. The standard deviations are obtained from three tests with different sensors.

Fig. 5. Distribution of electric field intensity of (a), (c) the conventional 50 nm Au-SPR sensor and (b), (d) the PC-SPR sensor. The field intensity is obtained using finite-difference time-domain (FDTD) simulations provided by the Lumerical Solutions software.

Fig. 6. Reflectance spectra for the PC-SPR sensors versus BSA concentration ranging from 0 to 15  mg·mL−1. (b) Linear fitting of the average resonant wavelength for different BSA concentrations; the standard deviations are obtained from three tests with different sensors.