Hybrid plasmonic modes for enhanced refractive index sensing

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.