Interpretation of Mode-Coupled Localized Plasmon Resonance and Sensing Properties

Plasmonic nanostructures support localized surface plasmon resonances (LSPRs) which exhibit intense light–matter interactions, producing unique optical features such as high near-field enhancements and sharp spectral signatures. Among these, plasmon hybridization (PH) and Fano resonance are two key phenomena that enable tunable spectral responses. In this study, we systematically investigate four representative nanostructures: a simple nanogap dimer (i-type structure), a dolmen structure, a heptamer nanodisk cluster, and a nanoshell particle. We utilize the discrete dipole approximation (DDA) to analyze these structures. The scattering, absorption, and extinction spectra, are calculated, and the near-field electric field vector distributions are visualized to distinguish between hybridized plasmon modes and Fano-type interference. These simulated results reveal that the observation of PH-like characteristics in a dolmen structure exhibiting typical Fano resonance under specific conditions, and conversely, the observation of Fano resonance-like characteristics in the well-known i-structure exhibiting PH, can be comprehended by considering the scattering spectrum and absorption spectrum separately, rather than the extinction spectrum, and by considering the electric field vector rather than the electric field intensity. Finally, the sensitivity of these nanostructures against the ambient medium was evaluated.