Resazurin
Resazurin is a blue, weakly fluorescent phenoxazine dye that metabolically active cells reduce to resorufin, a pink and strongly fluorescent compound. Because of this colour and fluorescence change, it is widely used as a redox indicator in cell viability, proliferation and cytotoxicity assays. It is also used in microbiological testing and as an oxygen indicator in anaerobic media. It is usually supplied as the sodium salt.
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Resazurin sodium salt
We manufacture and supply Resazurin sodium salt. See specifications, pack sizes and pricing, or ask us for a quote.
Resazurin (7-hydroxy-3H-phenoxazin-3-one 10-oxide) is a redox-sensitive dye. In the laboratory it is most often handled as the water-soluble sodium salt.
How does resazurin work as an indicator?
In its oxidised form, resazurin is blue and only weakly fluorescent. Viable cells reduce it irreversibly to resorufin, mainly through intracellular reductases and electron carriers such as NADH and NADPH. Resorufin is pink and strongly fluorescent, with emission at roughly 585–590 nm.
The signal can be read by absorbance or by fluorescence. It is generally proportional to the number of metabolically active cells.
Under strongly reducing conditions, resorufin can be reduced further to colourless dihydroresorufin. This step is reversible. It underlies the dye's use as an oxygen and redox indicator in anaerobic culture media.
Where is resazurin used?
- Cell-based assays: viability, proliferation and cytotoxicity testing in microplate formats. Several commercial ready-to-use reagents are based on resazurin.
- Microbiology: antimicrobial susceptibility testing, such as microdilution methods, and assessment of bacterial activity, including dairy quality tests.
- Anaerobic culture: visual confirmation that a medium remains reduced.
Resazurin assays are generally non-lytic, so cells can often be used for further analysis afterwards.
What should buyers check when sourcing resazurin?
- Confirm the form (sodium salt or free acid) and the CAS number.
- Review the CoA for dye content and purity. HPLC data is useful here.
- Check solubility and appearance specifications.
- Store the dye protected from light.
Review the SDS for GHS classification and handling requirements. Where relevant, also check REACH or TSCA status for your region.
Related concepts
Resazurin is closely related to resorufin, its reduced fluorescent product. It is often compared with tetrazolium-based viability assays such as MTT, XTT and WST-8, and with ATP-based luminescence assays. Related topics include fluorescence microplate reading, redox indicators and minimum inhibitory concentration (MIC) testing.
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