  Compared to single nanoparticles, strongly coupled plasmonic nanoparticles
provide attractive advantages owing to their ability to exhibit multiple
resonances with unique spectral features and higher local field intensity.
These enhanced plasmonic properties of coupled metal nanoparticles have been
used for various applications including realization of strong light-matter
interaction, photocatalysis, and sensing applications. In this article, we
review the basic physics of hybrid plasmonic modes in coupled metallic
nanodimers and assess their potentials for refractive index sensing. In
particular, we overview various modes of hybrid plasmons including bonding and
antibonding modes in symmetric nanodimers, Fano resonances in asymmetric
nanodimers, charge transfer plasmons in linked nanoparticle dimers, hybrid
plasmon modes in nanoshells, and gap modes in particle-on-mirror
configurations. Beyond the dimeric nanosystems, we also showcase the potentials
of hybrid plasmonic modes in periodic nanoparticle arrays for sensing
applications. Finally, based on the critical assessment of the recent
researches on coupled plasmonic modes, the outlook on the future prospects of
hybrid plasmon based refractometric sensing are discussed We believe that,
given their tunable resonances and ultranarrow spectral signatures, coupled
metal nanoparticles are expected to play key roles in developing precise
plasmonic nanodevices with extreme sensitivity.
