Since the understanding of DNA organization and structure in vivo is so important, fluorescent staining techniques using organic DNA-binding molecules are required for biological research and medical diagnosis, including cellular imaging and DNA quantification. However, membrane-permeable DNA-specific stains are uncommon. The minor groove binders 4',6-diamidino-2-phenylindole (DAPI) and Hoechst 33258 are presently used for DNA-specific staining, but they require ultraviolet excitation, which can lead to cellular damage due to lengthy irradiation. SYTO stains do provide cell-permeable dyes excitable by visible and near-infrared radiation. Unfortunately they are not specific nuclear stains, and moreover are of undisclosed chemical structures. Although the cell-permeant anthraquinone dye DRAQ5 shows red fluorescence emission and DNA-specific labeling, it is a DNA intercalator, which seriously interferes with the structure and function of nuclear DNA, in contrast to the minor groove binders such as SYT017.
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