Effective optical properties of nanoparticle-mediated surface plasmon resonance sensors

We investigate effective medium properties of nanoparticles (NPs) in surface plasmon (SP) resonance detection. Attention was paid to the effective medium characteristics with respect to the particle distribution in equally spaced, aggregated, and intermediate models, although effects of other parameters such as size, material, and concentration were also explored. The results suggest that the distribution may cause significant measurement deviation by as much as 20% for gold NPs and less than 5% for silica. Particle concentration showed complicated dependence in the effective medium. Different mechanisms were observed to govern effective medium properties of dielectric and metal NPs, SP mode transition and multiple scattering for silica NPs. In contrast, metal damping dominated resonance characteristics for gold NPs. The results are expected to provide fresh insights on how to apply an effective medium and interpret measured data in SP resonance sensors and beyond.