Biophysics

The Quadruple Jump

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Science  28 May 2004:
Vol. 304, Issue 5675, pp. 1213
DOI: 10.1126/science.304.5675.1213c

Rather like metal wires conduct electrons, photonic wires conduct light via transfers of excited-state energy. Heilemann et al. have designed a DNA-based wire that uses Förster resonance energy transfer across four donor-acceptor pairs of chromophores, such that excitation of Rhodamine Green at 488 nm (violet) results in emission from Atto 680 at 705 nm (red); in between, energy passes through tetramethylrhodamine, Atto 590, and LightCycler Red. The dyes are spaced 3.4 nm apart by attaching them to short DNA strands at 10-nucleotide (nt) intervals, and then hybridizing these short pieces to a 60-nt backbone. The maximal efficiency is about 90%, but a number of factors combine to lower the yield when measured in bulk. On the other hand, single-molecule spectroscopy uncovers the heterogeneity, with each spot exhibiting a predominant emission through only one of the five chromophores. Confirmation that the energy is transferred stepwise comes from prolonged excitation of single molecules, which results in sequential photobleaching and a shift in the emission from the red back toward the blue. — GJC

J. Am. Chem. Soc. 10.1021/ja049351u (2004).

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