The energy donor and acceptor are attached on different ends of a DNA template. The distance gap between donor and acceptor results in no direct energy transfer from donor to acceptor. (In other words, we observe that only donor is luminous.) The cyanine dyes K21 (green) can bind onto DNA template to form a dye aggregate acting as a bridge to fill in such geometric gaps, mediating efficient energy transfer from donor to acceptor through the aggregate with a length of up to 32 nanometers. (In this case, the acceptor is illuminated due to the energy transfer from the donor.)

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