DNA-based nanomaterials: Towards the design of self-assembled artificial light-harvesting units

Supramolecular artificial light harvesting complexes have been designed through binding of a donor dye to DNA, an acceptor dye to a protein and assembling the protein on the DNA allowing for efficient energy transfer between the DNA-bound donor and the protein-bound acceptor. Such artificial light harvesting complexes could be useful in sensitizing solar cells. In order to create successful DNA-based artificial light harvesting complexes, DNA-ligand and protein-ligand interactions were studied and suggested that small changes to functional groups on the ligands have a significant impact on the binding affinity of the ligands for the macromolecules. A set of DNA-binding ligands with different numbers of methylenes lowered had decreased binding free energy, ΔGbind , by –0.07 kcal/mol/methylene. Protein-ligand interactions were also studied with the binding of coumarins derivatives to serum albumins. In order to understand better how to apply artificial light harvesting units created with solar cells, the thermodynamics of interactions between proteins or DNA with a model solid were studied. Binding of proteins to the negatively charged model solid, α-ZrP, suggested the net charge of the protein, the number of atoms and buffer counterions affected proteins binding to the solid. The knowledge gained from ligand-DNA, ligand-protein and protein-solid interactions allowed for better design of DNA-based materials for light harvesting. ^ Artificial light harvesting units were created where a donor dye and an acceptor dye were bound simultaneously to one protein molecule. Excitation spectra clearly showed donor sensitized emission from the acceptor, and this process was sensitive to the protein structure. Efficient energy transfer between micromolar concentrations of the donor and acceptor were noted, though a significant amount of donor emission was still present in the emission spectrum. More efficient, DNA-based artificial light harvesting units were created with donor bound DNA, and acceptor bound to chemically modified cationic protein, in a supramolecular complex. Energy transfer was very efficient, as the majority of the donor emission was quenched by micromolar concentrations of the acceptor. Successful DNA-based materials for artificial light harvesting have been created, and that efficient energy transfer can be obtained from these materials.