Controlling plasmonic coupling and fluorescence energy transfer through organic adaptors

In the first part of this thesis, we have investigated and developed a measurement technique that is based on the plasmonic interaction of nanoparticles (NPs) and a metallic film. Charged gold NPs, which are interlinked with biomolecules to a gold film, compress or stretch the linkers according to the applied potential. The movement of the particles can be observed optically as their scattering color changes from green to red when the distance to the surface is decreased. We aimed to determine the conditions for single molecule experiments and present therefore a flexible platform, which allows the investigation of the fundamental behavior of particle displacements on the nanoscale and the resulting resonance shifts due to plasmonic interactions. In more detail, we determined the factors for persistent, reversible distance modulations, i. e. favorable combinations of NP surface modifications, SAMs, salinity, potential range and potential frequency in a newly developed optical setup. We also probed elastic properties of polymer layers. Here, the frequency of the driving potential was increased and cutoff frequencies were determined. Silver NPs are expected to show even a higher red-shift when approaching a gold film. In this sense, we investigated a possibility of silver NP growth in solution on the basis of the reaction of the Tollens’ regent with glucose and determined with extinction spectra and dynamic light scattering measurements suitable reaction regimes. The second part of this thesis deals with the bottom-up self-assembly of a DNA based photonic wire. We used three different types of fluorophores to transport energy from one end to the other end of double stranded DNA. The initial donor chromophore and the final energy acceptor were attached at the ends of the DNA rod, whereas in between an intercalating cyanine dye was used. The controlled placement of the dyes along the DNA strand leads to a very efficient energy transport along the wire compared to an unordered assembly. We realized the programmable placement of dyes with polyamides (PAs), which bind to specific DNA sequences. Three different wire architectures were studied: They differed in the overall length (from 21mer to 80mer) and in the number of PA binding sites (one to six). The PA binding sited were chosen in a way to keep the dye-to-dye distance constant. Steady state fluorescence emission measurements were use to evaluate the end-to-end energy transfer efficiencies. We found for all three DNA lengths significantly higher transfer efficiencies if the location of YO was determined by PAs.