Coupled oscillators’ approach to modelling a graphene-based plasmonic sensor

Sensing based on surface plasmon resonances (SPRs) is a popular idea for selectively detecting (bio-) molecules. With plasmon resonances due to noble metals, in the form of thin films or nanoparticles, occurring in the visible spectral range, the selectivity is achieved by functionalizing the surface in order to enhance adhesion of the targeted molecular species. An alternative idea is to use SPRs produced by graphene electrons, in the THz-FIR range, where characteristic vibrational modes of many important molecules occur. It has been demonstrated experimentally with graphene nanoribbon superlattices. Due to superposition of a narrow molecular resonance (dipole-active vibration mode) and the broad plasmonic band, Fano-type resonances were found, caused by an interference between a resonant state (molecular vibration) and a broad continuum (SPR band). Originally predicted as a quantum phenomenon, the Fano resonance has a classical analogy that can be exemplified by coupled harmonic oscillators. We demonstrate the capability of this approach for modelling graphene-based plasmonic sensors and discuss its advantages.