In natural systems, the arrangement of functional molecules and groups with regulated distances, orders and orientations provide highly efficient functionality. For example, in natural photo-synthetic systems, the arrangement of porphyrin derivatives with regulated distance and geometry through non-covalent interaction provide highly efficient photo-induced energy transfer. Arrangement of chromophores (multi-chromophore array) would therefore provide a good model for artificial photosynthetic systems. A single chain of oligo-DNA is able to interact specifically with its complementary counterpart chain through sequence-specific hydrogen bonding. Focusing on this property of DNA, a wide variety of non-covalent binding pairs, binding donors and binding acceptors, with high specificity and stability can easily be provided simply by varying the oligo-DNA sequences. Oligo-DNA is therefore a useful tool as “molecular glue” for constructing of nano-architecture and molecular assembly systems. We demonstrated the construction of one-dimensional polyassembly using anti-directed comple-mentary DNA dimers consisting of aromatic core (chromophore model) and two strand of anti-directed oligo-DNA. Moreover, we constructed sequential arrays of chromophores at regulated distances on a non-covalent DNA molecular assembly system using 10mer oligo-DNA/chromophore conjugates and 30 or 40mer matrix oligo-DNA in aqueous media. Photo-induced fluorescence resonance energy transfer (FRET) behaviors were observed in the chromophore array. Such molecular assembly systems using oligo-DNA should be useful for construction of good models for a photo-energy transmission system mimicking photosynthetic systems or nanometer scale architectures.

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With decreasing size of particles to nanometer level, the surface-to-volume ratio is largely increasing as well as the mobility and reactivity, and the dispersion of nanoparticles is dominated by thermodynamic and quantum fluctuation. Compared with bulk-sized materials, nanomaterials show the unique physical properties such as optical property of semiconducting materials by quantum-size effect, quantum-tunneling effect of magnetic materials. Currently, nanotechnology has been rapidly applied to biological systems and many bioconjugate nanomaterials have been developed with new concepts, especially in the fields of separation and detection of biomolecules, and regulation of biological reactions. This article reviews a variety of new applications of these materials for advance of biotechnology, which include biosensing systems using various gold nanoparticles, quantum dots-based fluorescence labeling techniques, and separation/detection of biomolecules using pH- or temperature-sensitive polymers and magnetic particles.

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We have proposed and demonstrated that a combination of porphyrins with fullerenes is an ideal system in artificial photosynthesis, because of the small reorganization energies of electron transfer, which allow us to realize photosynthetic electron transfer without a special environment such as protein matrix. A variety of porphyrin-fullerene linked systems have been prepared to reveal a long-lived charge-separated state (up to seconds) with an extremely high quantum yield (up to 99%), as attained in photosynthesis. Vectorial organization of such porphyrin-fullerene linked systems on gold and ITO electrodes have been achieved to convert light energy into chemical and electrical energies in a macroscopic quantity. In particular, mixed self-assembled monolayers of light-harvesting and charge separation molecules on the gold electrode have established a cascade of photoinduced energy transfer and multistep electron transfer, resulting in the production of photocurrent output with the highest quantum yield ever reported for photocurrent generation at monolayer-modified metal electrodes using donor-acceptor linked molecules. Porphyrin alkanethiolate monolayer-protected gold nanoclusters have been synthesized successfully to improve the light-harvesting properties.

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