Double-layered gold gratings as refractive index sensors with ultrahigh figure of merits

Abstract

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.