Use of biomolecular scaffolds for assembling multistep light harvesting and energy transfer devices

• Light harvesting systems require subnanoscale positioning of light sensitive molecules.
• Biological scaffolds have much to offer for positioning fluorophores.
• Biological scaffolds include DNA, peptides, viruses, and sugars.
• DNA in particular offers the most versatile 3-D structures for light harvesting.
• Integrating quantum dots into biologically assembled light harvesters is very promising.

The development of biologically templated artificial light harvesting antennae and energy transfer devices is a highly active research area with exceptional challenges. Natural energy harvesting complexes have exquisite spectrally- and spatially-tuned systems with high redundancy to maximize their ability to gather, channel, and distribute electromagnetic radiation. Attempting to mimic these highly efficient systems requires at the very least (sub)nanoscale precision in the positioning of light sensitive molecules, the latter of which must also possess carefully selected photophysical properties; in essence, these two fundamental properties must be exploited in a synergistic manner. First, the scaffold must be highly organized, ideally with multiple symmetrical components that are spatially arranged with nanoscale accuracy. Second, the structure must be amenable to chemical modification in order to be (bio)functionalized with the desired light sensitive moieties which have expanded greatly to now include organic dyes, metal chelates, fluorescent proteins, dye-doped and noble metal nanoparticles, photoactive polymers, along with semiconductor quantum dots amongst others. Several families of biological scaffolding molecules offer strong potential to meet these stringent requirements. Recent advances in bionanotechnology have provided the ability to assemble diverse naturally derived scaffolds along with manipulating their properties and this is allowing us to understand the capabilities and limitations of such artificial light-harvesting antennae and devices. The range of scaffold or template materials that have been used varies from highly symmetrical virus capsids to self-assembled biomaterials including nucleic acids and small peptides as well as a range of hybrid inorganic–biological systems. This review surveys the burgeoning field of artificial light-harvesting and energy transfer complexes that utilize biological scaffolds from the perspective of what each has to offer for optimized energy transfer. We highlight each biological scaffold with prominent examples from the literature and discuss some of the benefits and liabilities of each approach. Cumulatively, the available data suggest that DNA is the most versatile biological material currently available, though it has challenges including precise dye placement and subsequent dye performance. We conclude by providing a perspective on how this field will progress in both the short and long term, with a focus on the transition to applications and devices.

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