Sulforhodamine B (SRB) Cell Cytotoxicity

The sulforhodamine B (SRB) cytotoxicity assay is a simple, sensitive and reproducible method for cell density determination, which relies on the binding ability of SRB dye to basic amino-acid residues of cellular proteins. Under mild acidic conditions, the protein components of the cells can bind to SRB dye and are subsequently extracted under basic conditions. The method was developed in 1990, and is still one of the most widely used assays for in vitro cytotoxicity screening. As the binding of SRB is stoichiometric, the amount of extracted dye is proportional to cell mass and therefore is indicative of the number of cells in a sample.The fixed dye is solubilized and colorimetrically measured at OD 565 nm (550-580 nm is acceptable) with a reference filter of 690 nm. The OD values correlate with total protein content and thus with cell number.In comparison to formazan-based assays (e.g. MTT or XTT assays), SRB provides a higher signal-to-noise ratio and a better linearity with cell number. Additionally, due to its nondestructive and stable endpoint, SRB measurement is not time sensitive. These advantages make the SRB assay suitable for large scale cytotoxicity screening.

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