Oxazole yellow homodimer (also know as YOYO-1) is a cell-impermeant, high-affinity carbocyanine monomeric nucleic acid stain that is essentially nonfluorescent in the absence of nucleic acids but exhibits excitation/emission maxima 491/509 nm when bound to nucleic acids. Oxazole yellow homodimer is useful as a dead cell selective stain in live cultures.