Self-assembled DNA photonic wire for long-range energy transfer.

DNA is a promising material for use in nanotechnology; the persistence length of double stranded DNA gives it a rigid structure in the several-nanometer regime, and its four letter alphabet enables addressability. We present the construction of a self-assembled DNA-based photonic wire capable of transporting excitation energy over a distance of more than 20 nm. The wire utilizes DNA as a scaffold for a chromophore with overlapping absorption and emission bands enabling fluorescence resonance energy transfer (FRET) between pairs of chromophores leading to sequential transfer of the excitation energy along the wire. This allows for the creation of a self-assembled photonic wire using straightforward construction and, in addition, allows for a large span in wire lengths without changing the basic components. The intercalating chromophore, YO, is chosen for its homotransfer capability enabling effective diffusive energy migration along the wire without loss in energy. In contrast to heterotransfer, i.e., multistep cascade FRET, where each step renders a photon with less energy than in the previous step, homotransfer preserves the energy in each step. By using injector and detector chromophores at opposite ends of the wire, directionality of the wire is achieved. The efficiency of the wire constructs is examined by steady-state and time-resolved fluorescence measurements and the energy transfer process is simulated using a Markov chain model. We show that it is possible to create two component DNA-based photonic wires capable of long-range energy transfer using a straightforward self-assembly approach.