CAS 3520-42-1 Sulforhodamine B (SRB, C.I. Acid Red 52) is a cationic oxygenanthraquinone red fluorescent dye. It is a dark red powder with good water solubility. Its maximum absorption is 565 nm and maximum emission is 586 nm. It has excellent photostability. Under weakly acidic conditions, it can combine with intracellular basic amino acids and cannot penetrate the cell membrane. This substance is most commonly used in the classic SRB method in the scientific research field, for conducting high-throughput screening of in vitro cell proliferation and anti-tumor drugs. It can also be used for fluorescence staining of tissue sections and water-phase fluorescence tracing. At the same time, as an acidic dye, it can be used for coloring wool, silk, nylon and other textiles as well as leather and paper.