Rhodamine B is a fluorescent dye used in microscopy to stain bacteriological smears and tissue sections of human origin. Used in human-medical cell diagnosis for bacteriological and histological investigations. It works with binds non-specifically to a substrate, similar to the Ziehl-Neelsen method.It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with fluorometers.Rhodamine B is 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. Rhodamine dyes are also used extensively in biotechnology applications such as fluorescence microscopy, flow cytometry, fluorescence correlation spectroscopy and ELISA.In California, rhodamine B is suspected to be carcinogenic and thus products containing it must contain a warning on its label. Cases of economically motivated adulteration, where it has been illegally used to impart a red color to chili powder, have come to the attention of food safety regulators.