Oxazole yellow, also know as YO-PRO-1, is a green-fluorescent, cell-impermeant, high-affinity carbocyanine monomeric nucleic acid stain. The dye is nonfluorescent in the absence of nucleic acids but exhibits excitation/emission maxima at 491/509 nm when bound to nucleic acids. Oxazole yellow is also used to identify apoptotic cells. Early apoptotic cells become permeant to oxazole yellow, but remain impermeant to propidiumiodide, a dead cell stain. Properties: Orange solution; Ex/Em= 491/509 nm (with DNA); Store at -20°C and protect from light; C24H29I2N3O, MW: 629.32; [152068-09-2].