Acridine Orange Base, a cell-permeable fluorescent dye, selectively stains organisms (bacteria, parasites, viruses, etc.) bright orange and differentiates human cells in green under specific conditions (pH=3.5, Ex=460 nm), facilitating their detection via fluorescence microscopy. It exhibits green fluorescence upon binding to dsDNA (Ex=488, Em=520-524) and turns red with ssDNA (Ex=457, Em=630-644) or ssRNA (Ex=457, Em=630-644), making it useful in cell cycle assays [1] [2] [3].