Separation of nucleic acids by capillary electrophoresis in cellulose solutions with mono- and bis-intercalating dyes

The effects of bis- and mono-intercalating dyes on the capillary electrophoretic separation of double-stranded DNA have been investigated in buffers containing (hydroxypropylmethyl)-cellulose. Broad bands and incomplete separations of phi X 174 DNA HaeIII digest were obtained with the bis-intercalators ethidium homodimer 1 (EthD-1) and ethidium homodimer 2 (EthD-2), under a wide range of dye and polymer concentrations. The above results were attributed to the presence of several intramolecular dye/DNA complexes for each fragment. For EthD-2/DNA complexes, but not for EthD-1/DNA complexes, additional bands beyond the expected number of fragments were observed. The extra bands were attributed to formation of intermolecular dimers. Use of the monomeric intercalating dyes, ethidium and propidium, allowed complete separation of all fragments of phi X 174 DNA HaeIII digest. A low-power green He-Ne laser (543.6 nm) was shown to be satisfactory for laser-induced fluorescence detection with any of these dyes.