Spectroscopic study of cyanine dyes interacting with the biopolymer, DNA

Dyes intercalated into DNA strands or bound to grooves show fluorescence intensity changes and aggregate formation depending on the conditions. In order to establish some empirical rules concerning dye intercalation, spectroscopic studies for the effects of DNA on several series of cyanine dyes with different aromatic rings, conjugated chain length and alkyl substituents were made. Absorption spectra, fluorescence intensity and circular dichroism spectra showed strong dependence on the species of dyes. Combination of preceding studies and these present results indicates that cyanine dyes tend to intercalate into DNA strand if their polymethine bridge was composed of only one carbon. For molecules with the longer chains irregular aggregates were formed by small amounts of DNA, which transformed into complexes composed of multiple dye and DNA strands. These results would serve as a useful guideline for designing of optical functional materials and devices utilizing DNA complex.

► Fluorescence enhancement of cyanine dyes coupled with DNA depends on their structure.
► Fluorescence and circular dichroism spectra strongly depend on dye molecular size.
► Dye intercalation likely takes place for smaller sized cyanine dyes.