Refractive index (RI) sensors based on localized surface plasmon resonances (LSPR) have attracted lots of attentions due to its potential applications in "point-of-care" clinical devices. In this presentation, we will review the progress in the field of LSPR-based RI sensor. Then LSPR-based RI sensing properties of double-layered gold gratings separated by dielectric gratings were studied. Two-dimensional double-layered gold gratings, named as gold mushroom arrays, show a superior advantage as a LSPR-based RI sensor because their figure of merits can reach 108 as high as the theoretical predicted upper limit for the propagating surface plasmon resonance (PSPR)-based RI sensor. However, such a high FOM is obtained under a detection light with an oblique incident angle which is still not a favorable testing scheme, because it increases the complexity of the system. Therefore, we also proposed another RI sensor based on one-dimensional double layer gold gratings working under normal incidence, which gives a high FOM as well.
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