The efficiency of chemical energy production of a photosynthetic system can be strongly enhanced in the presence of metal nanoparticles. Two competing effects contribute to the photosystem efficiency: plasmon enhancement of photon fields inside the light-absorbing chlorophyll molecules and energy transfer from chlorophylls to metal nanoparticles. The first effect can lead to strong enhancement of light absorption by the chlorophylls, whereas the second can somewhat reduce the quantum yield of the system. This paper describes one concrete example of hybrid photosystem that incorporates a photosynthetic reaction center bound to gold and silver nanocrystals. The calculated rate of production of excited electrons inside the reaction center is strongly increased due to plasmon resonance and fast electron-hole separation. In phototransport experiments with photosynthetic reaction centers, the plasma resonance can enhance the photocurrent response. The enhancement mechanism described here can be utilized in energy-conversion devices and sensors.

Nanoparticle/nanowire assemblies with a degree of radial organization were prepared around luminescent semiconducting CdTe nanowires using bioconjugation with streptavidin and D-biotin linkers. Red-emitting nanowires (6.62 +/- 1.55 nm diameter, 512 +/- 119 nm length) and green-emitting nanoparticles (3.2 +/- 0.7 nm diameter) were surface-modified with biotin, while orange-emitting nanoparticles (4.1 +/- 1.2 nm diameter) were decorated with streptavidin. CdTe nanocrystals produced two fuzzy layers around the nanowires in which the diameter of CdTe nanoparticles decreased with the distance from the nanowire axis. Förster resonance energy transfer (FRET) from the outside layer of nanoparticles to the central nanowire was observed for nanowires conjugated with 4.1 nm CdTe. Addition of 3.2 nm CdTe resulted in a red-orange-green optical progression with band gaps of CdTe decreasing toward the axis of the superstructure. In this case, 4-fold luminescence enhancement of the nanowire luminescence was observed and was attributed to multistep FRET. This observation indicated the accumulation of photogenerated excitons in the cascade terminal. A simple model of multiconjugated superstructure with cascade energy transfer is developed and used to describe and understand the experimental data. The experimental data and theoretical model suggest the possibility of utilization of the prepared superstructures with radial symmetry in several classes of optoelectronic devices including nanomaterials for energy collection. They can also be a convenient model object for the investigation of methods of energy funneling in nanoscale assemblies.