Thiazole orange dimer YOYO-1 is a green fluorescent dye used for DNA staining. It is a tetracationic homodimer of oxazole yellow (YO) and is typically provided as a tetraiodide salt. In aqueous buffer, the free YOYO-1 dye (λmax 458 nm; λmax 564 nm) exhibits low fluorescence quantum yield, but upon binding to double-stranded DNA through diintercalation, its fluorescence intensity increases by 3200 times (λmax 489 nm; λmax 509 nm).