Sulforhodamine B or Kiton Red 620 (C<sub>27</sub>H<sub>30</sub>N<sub>2</sub>O<sub>7</sub>S<sub>2</sub>) is a fluorescent dye with uses spanning from laser-induced fluorescence (LIF) to the quantification of cellular proteins of cultured cells. This red solid dye is very water-soluble.
The dye has maximal absorbance at 565 nm light and maximal fluorescence emission at 586 nm light. It does not exhibit pH-dependent absorption or fluorescence over the range of 3 to 10.
Sulforhodamine B is often used as a membrane-impermeable polar tracer or used for cell density determination via determination of cellular proteins (cytotoxicity assay).