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.

Photosystem I (PS I) is a transmembrane, multi-subunit protein-chlorophyll complex that mediates vectorial, light-induced electron transfer. The nanometer-sized dimensions, an energy yield of approximately 58 %, and the quantum efficiency of almost 1 [1] make the reaction center a promising unit for applications in molecular nanoelectronics. PS I is located in the thylakoid membranes of chloroplasts and cyanobacteria. It mediates light-induced electron transfer from plastocyanin or cytochrome C 553 to ferredoxin. [2,3] The crystalline structure of PS I from Synechococus elongatus and from plants' chloroplast was resolved to 2.5 and 4.4 Å, respectively. [4,5] In cyanobacteria, the complex consists of at least 12 polypeptides, some of which bind 96 light-harvesting chlorophyll molecules. The electron-transport chain contains P700, A 0 , A 1 , F X , F A , and F B , representing a chlorophyll a dimer, a monomeric chlorophyll a, two phylloquinones, and three [4Fe-4S] iron-sulfur centers, respectively. The reaction-center core complex is made up of the heterodimeric PsaA and PsaB subunits, containing the primary electron donor, P700, which undergoes light-induced charge separation and transfers an electron through the sequential carriers A 0 , A 1 , and F X . The final acceptors, F A and F B , are located on another subunit, PsaC. The redox potential of the primary donor, P700, is +0.43 V and that of the final acceptor, F B , is -0.53 V, producing a redox difference of -1.0 V. The charge separation spans about 5 nm of the height of the protein, representing the center-tocenter distance between the primary donor and the final acceptor. The protein complex is 9 nm in height and has a diameter of 21 nm and 15 nm for the trimer and the monomer, respectively.[4] The photoactivity and the nanometer-sized dimensions make this complex a promising unit for applications in molecular nanoelectronics. In earlier works, care was taken to indirectly attach plant PS I [6,7] and bacterial reaction centers [8,9] to solid surfaces in attempts avoid inactivation of selfassembled monolayers.In this work, we devised a system that overcame the problems arising from direct covalent binding of proteins to metal surfaces. We selected the robust PS I reaction centers from the cyanobacteria Synechocystis sp. PCC 6803. The main reason for the structural stability of this PS I is due to the fact that all chlorophyll molecules and carotenoids are integrated into the complex of core subunits, while, in plant and bacterial reaction centers, the antenna chlorophylls are bound to chlorophyll-protein complexes that are attached to the core subunits. Indeed, there was no need to use peptide surfactants, which were essential for stabilization of plant PS I and the bacterial reaction centers. [7] A careful selection of the amino acids, which were modified to cysteines for covalent attachment of the PS I to the gold surface, was the second factor that insured structural and functional stability of the self-assembled, oriented PS I. The rational design was b...

Unique occurrence of magnetism is shown, in which magnetism appears ex nihilo, when organic molecules are self-assembled as monolayers on gold substrate. The molecules as well as the substrate, when they stand alone, are diamagnetic. Using a superconducting quantum interference device type magnetometer we obtained direct evidence that close-packed organized thio-organic films adsorbed on gold substrates possess magnetic properties at room temperature. The films studied show very high specific magnetization, up to many tens Bohr magnetons per adsorbed molecule, with a very small hysteresis. It is highly anisotropic and shows almost no temperature dependence. The magnetism observed is related to charge transfer between the organic layer and the metal substrate. Yet, the uniqueness here is that many spins are polarized per adsorbed molecules. The magnetic effect is related to the two dimensional organization of the organic molecules on the metal substrate which might explain the high anisotropy.

The photosystem I (PS I) protein is one of nature's most efficient light harvesting complexes and exhibits outstanding optoelectronic properties. Here we demonstrate how metal nanoparticles which act as artificial antennas can enhance the light absorption of the protein. This hybrid system shows an increase in light absorption and of circular dichroism over the entire absorption band of the protein rather than at the specific plasmon resonance wavelength of spherical metal nanoparticles (NPs). This is explained by broad-resonant and nonresonant field enhancements caused by metal NP aggregates, by the high dielectric constant of the metal, and by NP-PS I-NP antenna junctions which effectively enhance light absorption in the PS I.