Noble metal nanoparticle pairs: effect of medium for enhanced nanosensing.

In this Letter, we show using both a quasi-static model and discrete dipole approximation simulations of nanoparticle pairs that the surface plasmon resonance shift resulting from the electromagnetic coupling between noble metal nanoparticles increases with an increase in the dielectric constant of the medium. As the particle pair partners approach each other, there is an increase in the rate at which the plasmon resonance shifts in response to a medium refractive index change. Thus, the surface plasmon resonance of a plasmonic nanoparticle pair exhibits higher sensitivity to the environment/medium refractive index as compared to an isolated nanoparticle. The medium sensitivity of the particle pair is shown to increase near exponentially with a decrease in the interparticle separation between the nanoparticles. We therefore propose that enhanced plasmon resonance nanosensing may be achieved by employing coupled particles instead of colloids or arrays of noninteracting particles.