Fluorescence of ethidium bromide in alcohol–water solutions
Spectroscopic studies have shown that various optical properties of ethidium bromide (EB) in alcohol–water solvents display a close correlation with the binding energy of the dye to DNA. Although it is known that the spectroscopic properties of a solute may depend markedly upon its interaction with the solvent, the results show that bulk solvent properties such as polarity, viscosity and pH do not account for the observed data. It appears instead that local effects (solvation) are responsible for the changes of optical properties of the dye. In particular, fluorescence efficiency measurements suggest that alcohol and water molecules have different affinities for different regions of the dye, in agreement with the amphiphilic nature of the ethidium cation.