SPP-MIM hybridization meta-film: a biosensing structure uniting the merits of SPR and LSPR (2509.16668v1)

Abstract: Having a flat device-solution interface is crucial for nanophotonic biosensors to achieve stable and reproducible performance, by mitigating solid-liquid-gas interfacial processes at the nanometer scale. In this aspect, the metal-insulator-metal (MIM) film presents a capable solution, by hybridizing surface plasmon polaritons (SPP) and MIM gap plasmons, which is enabled by the latter's unique dispersion characteristic and wide tunability. In this meta-film, the SPPs propagate along a flat interface, and seal the gap plasmons which can be integrated with nanostructures, e.g., a coupling grating. In addition, by tuning the gap plasmons, the SPP-MIM hybridization meta-film can be designed to achieve a significantly reduced SPP evanescent depth and a significantly improved surface sensitivity. Using gold as the plasmonic material, such improvements are theoretically predicted across a broad spectral range, from visible to near infrared. Particularly, at 1550 nm, we show that a grating-coupled meta-film device is designed to have its evanescent depth shortened from 1.4 micrometers to 0.16 micrometers, with an enhancement factor of 5.6 in its surface sensitivity, as compared with traditional grating-coupled SPR. This unique characteristic of the SPP-MIM meta-film makes it an efficient combination of propagating SPR and LSPR, by simultaneously having a flat and simple biosensing interface, a short evanescent depth and a high surface sensitivity. It provides an inspiring approach for transforming various LSPR designs into stable biosensors.