Self-Assembled Quantum Dot-Sensitized Multivalent DNA Photonic Wires

Combining the inherent scaffolding provided by DNA structure with spatial control over fluorophore positioning allows the creation of DNA-based photonic wires with the capacity to transfer excitation energy over distances greater than 150 A. We demonstrate hybrid multifluorophore DNA-photonic wires that both self-assemble around semiconductor quantum dots (QDs) and exploit their unique photophysical properties. In this architecture, the QDs function as both central nanoscaffolds and ultraviolet energy harvesting donors that drive Forster resonance energy transfer (FRET) cascades through the DNA wires with emissions that approach the near-infrared. To assemble the wires, DNA fragments labeled with a series of increasingly red-shifted acceptor-dyes were hybridized in a predetermined linear arrangement to a complementary DNA template that was chemoselectively modified with a hexahistidine-appended peptide. The peptide portion facilitated metal-affinity coordination of multiple hybridized DNA-dye structures to a central OD completing the final nanocrystal-DNA photonic wire structure. We assembled several such hybrid structures where labeled-acceptor dyes were excited by the QDs and arranged to interact with each other via consecutive FRET processes. The inherently facile reconfiguration properties of this design allowed testing of alternate formats including the addition of an intercalating dye located in the template DNA or placement of multiple identical dye acceptors that engaged in homoFRET. Lastly, a photonic structure linking the central QD with multiple copies of DNA hybridized with 4-sequentially arranged acceptor dyes and demonstrating 4-consecutive energy transfer steps was examined. Step-by-step monitoring of energy transfer with both steady-state and time-resolved spectroscopy allowed efficiencies to be tracked through the structures and suggested that acceptor dye quantum yields are the predominant limiting factor. Integrating such DNA-based photonic structures with QDs can help create a new generation of biophotonic wire assemblies with widespread potential in nanotechnology.