Thiazole orange dimer YOYO 1 is a green fluorescent dye used for DNA staining. It belongs to the monomethine cyanine dye family and is a tetracationic homodimer of oxazole yellow (abbreviated as YO, hence the name YOYO), usually provided as a tetraiodide salt. In aqueous buffer, the free YOYO-1 dye (λmax 458 nm; λmax 564 nm) has a very low fluorescence quantum yield, but after binding to double-stranded DNA through diintercalation, the fluorescence intensity is increased by 3200 times (λmax 489 nm; λmax 509 nm).