Fig. 1. (a) Schematic diagram of the wavelength-interrogated SPR sensing device based on Kretschmann structure; (b) schematic diagram of the PSPR on the NPGF/air interface

Fig. 2. (a) SEM image of the NPGF; (b) black-white image obtained after automatical threshold processing of the SEM image with the Image J software

Fig. 3. (a) SPR spectra of the NPGF in the air measured by the experiment; (b) simulated SPR spectra using the combination of the Fresnel formula and the Bruggeman dielectric constant approximation equation

Fig. 4. (a) Spectral responses of the NPGF-SPR sensor to Pb2+ ions adsorbed from aqueous solutions of different concentrations when θ=-12°; (b) resonant-wavelength shifts as a function of the Pb2+ concentration

Fig. 5. Spectral response of the dense gold film based SPR sensor to Pb2+ ions adsorbed from an aqueous solution of 500 nmol·L-1 concentration when θ=-18°

Fig. 6. (a) Spectral responses of the NPGF-SPR sensor to melamine molecules adsorbed from aqueous solutions with different concentrations when θ=-12°; (b) resonant-wavelength shifts as a function of the melamine concentration