Computational study of the interaction of fluorophores with various metallic nanoparticle systems

Finite-difference time-domain calculations are used to study how fluorescence is modified when fluorophores are located in proximity to various metal nanoparticle systems. The fluorophore is modeled as a radiating point dipole with orientation defined by its polarization. The angle-resolved far-field distributions of the emission in a single plane are computed. The emission patterns show interesting intensity variations and angular profiles depending on the dipole orientation, size of the metal particles and the metal-dipole spacing. We also compute changes in the total radiated power through a closed volume containing the fluorophore and metal nanoparticles relative to an isolated fluorophore. This change in total radiated power is proportional to changes in the relative radiative decay rates of the fluorophore-metal system. Our results suggest a high dependence of the radiated power on the fluorophore orientation, particle size, metalfluorophore distance and particularly the presence of metal nanoparticle dimers. We examined the effect of a fluorophore on the near-fields around silver nanoparticles. The fields can be enhanced compared to the isolated fluorophore and exhibit interesting spatial variations around the nanoparticle that can be useful for applications involving molecular spectroscopy.