The cell-impermeant viability indicator ethdium homodimer-1 (EthD-1) is a high-affinity nucleic acid stain that is weakly fluorescent until bound to DNA and emits red fluorescence (Excitation/emission maxima ∼528/617 nm).
We recommend using high-quality anhydrous DMSO for a stock concentration of 1 to 2 mM in DMSO/H2O 1:4 (v/v).