Abstract
Room-temperature surface exciton polaritons (SEPs) were successfully demonstrated recently by replacement of the metal thin film in the Kretschmann-Raether configuration of surface plasmon polaritons (SPPs) with a film of the J-aggregate cyanine dye 5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl) benzimidazol-2-ylidene] propenyl]-1-ethyl-3-(4-sulfobutyl) benzimidazolium hydroxide (TDBC). Compared with SPPs (i.e., photons coupled to highly mobile free electrons at the metal surface), the coupling of photons to less-mobile excitons supports stronger field confinement at the TDBC surface. This extraordinary field confinement of SEPs beyond SPPs motivated us to explore the feasibility of refractive-index (RI) sensing, in particular, surface RI sensing. We find that the bulk RI sensitivity of 118 degrees (140 degrees) per refractive-index unit (RIU) of the proposed SEP sensor in the RI range from 1.0 to 1.001 (from 1.33 to 1.36) for a gaseous analyte (an aqueous solution) is higher than that of a conventional gold-based SPP sensor [73 degrees /RIU (124 degrees /RIU)]. For surface RI sensing, the SEP sensor has both higher sensitivity and a higher figure of merit than the SPP sensor. These numerical results undoubtedly reveal SEPs to be a promising mechanism for sensing.