Spectral Dependence of Fluorescence Enhancement in LH2-Au Nanoparticle Hybrid Nanostructures

We report on the influence of plasmon resonance in spherical gold nanoparticles on the optical properties of light-harvesting complex LH2 from the purple bacteria Rhodopseudomonas palustris. Systematic studies as a function of the excitation energy and the separation distance indicate that metal enhanced fluorescence shows strong dependence upon both of these parameters. We observe substantial increase of the fluorescence from LH2 complex in a hybrid nanostructure with 12 nm silica spacer. On the other hand, the enhancement measured with laser tuned into the plasmon resonance is almost threefold compared to the off-resonance configuration. The enhancement of fluorescence intensity originates in both cases from the increase of carotenoid absorption in the LH2 complex.