Fluorescence and Energy Transfer in Dye-Labeled DNA Crystals

DNA crystals make it possible to organize guest molecules into specific periodic 3D patterns at the nanoscale, and thereby to create novel macroscopic objects with potentially useful functionality. Here, we describe the fluorescence and energy transfer properties of DNA crystals that are self-assembled from DNA tensegrity triangles with covalently attached Cy3 and Cy5 dyes. When compared to reference DNA strands in solution, the fluorescence measurements indicate that the dyes in the crystal experience a more homogeneous environment, resulting in a 2-fold increase in Cy3 quantum yield and single-exponential Cy3 fluorescence decays. Energy transfer in a network of coupled Cy3 and Cy5 dyes in the DNA crystal is demonstrated experimentally. Numerical simulation finds the experiments to be consistent with a Förster model of the dyes in the periodic crystalline environment, and particularly if the transition dipoles are assumed random in orientation but static on the time scale of the excitation decay.