R 3068 (OTTO) Rhodamine B, for fluorescence Cas 81-88-9 - used in biology as a staining fluorescent dye, sometimes in combination with auramine O, as the auramine-rhodamine stain to demonstrate acid-fast organisms, notably Mycobacterium. R 3068 (OTTO) Rhodamine B, for fluorescence Cas 81-88-9 - used extensively in biotechnology applications such as fluorescence microscopy, flow cytometry, fluorescence correlation spectroscopy and ELISA.