Discovery of Cyanine Dye Aggregation on DNA

While the impact of cyanine dyes on the biological sciences has been substantial, recent work has led to investigation of cyanine-DNA interactions from a materials science perspective. This direction of research was motivated by a surprising 

In the case of the DNA solutions, neither the temperature nor the dye concentration was changed, indicating that the DNA was promoting aggregation of the dye. This was verified using circular dichroism (CD) spectropolarimetry, which takes advantage of the fact that achiral molecules exhibit no CD in solution, but when bound to a chiral molecule such as DNA can exhibit induced CD [19]. A strong, exciton coupled CD 

FIGURE 7.2 UV-vis (A) and CD (B) spectra recorded for cyanine dye DiSC2(5) in the presence of [Poly(dA-dT)]2. The blue-shifted absorption band and right-handed splitting pattern in the CD led to the conclusion that the dye assembled into a helical H-aggregate using the DNA as a template. 

Retnming to the inflnence of DNA in promoting aggregation of DiSC2(5), the question arose as to the specific interactions between the dye and nucleic acid. The spectral features observed in UV-vis and circular dichroism could be explained by stacking of the dyes along the exterior of the duplex to form columnar structures. 

FIGURE 7.3 Exciton coupling model and allowed optical transitions for J- and H-aggregated dyes. 

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