We propose a refractive index sensor based on the interference of two surface-plasmon waves on both surfaces of a gold film with a two-slit structure. The phase of the interference was solved, and the dispersion relation of the real part of Au dielectric function was considered. The sensor was performed with NaCl-H2O solutions of different concentrations and exhibited a linear response and a high sensitivity of 4547 nm/RIU (refractive index unit) to the refractive index change.
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Wu et al. (2009) studied this question.