Absorption, scattering, and extinction cross sections of a nanosphere with adjacent molecule.

While the electromagnetic interaction between noble metal nanoparticles with adjacent molecules has been known for some time, the exact expression of the scattering, absorption, and extinction cross sections of such a system has long remained unspecified. Herein, these cross sections are analytically derived for a molecule-nanoparticle system in which the molecule is excited to a radiating dipole by monochromatic incident radiation. These analytic cross sections were used in numerical calculations to model the UV-vis spectrum of a 20 nm gold nanoparticle colloid with attached IR-808 variant dye molecules. The numerical results compared favorably with experimental spectra.