Sulforhodamine B or Kiton Red 620 (C27H30N2O7S2) 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.

[1] The dye has maximal absorbance at 565 nm light and maximal fluorescence emission at 586 nm light.

[1] It does not exhibit pH-dependent absorption or fluorescence over the range of 3 to 10.

[2] Sulforhodamine B is often used as a membrane-impermeable polar tracer[3] or used for cell density determination via determination of cellular proteins (cytotoxicity assay).