Neutral red

Neutral red (toluylene red, Basic Red 5, or C.I. 50040) is a eurhodin dye used for staining in histology. It stains lysosomes red.^[1] It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital staining of blood. It can be used for staining the Golgi apparatus in cells and Nissl granules in neurons.

Neutral red

Neutral red
Solid Neutral Red Neutral Red Aqueous Solution
Names
IUPAC name N2,N2,7-Trimethylphenazine-2,8-diamine—hydrogen chloride (1/1)
Other names 3-Amino-7-dimethylamino-2-methylphenazine hydrochloride Toluylene red
Identifiers
CAS Number	553-24-2 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:86370 N
ChemSpider	10634 Y
ECHA InfoCard	100.008.215
EC Number	209-035-8
PubChem CID	11105
UNII	261QK3SSBH
CompTox Dashboard (EPA)	DTXSID90883440
InChI InChI=1S/C15H16N4.ClH/c1-9-6-13-15(8-11(9)16)18-14-7-10(19(2)3)4-5-12(14)17-13;/h4-8H,16H2,1-3H3;1H Y Key: PGSADBUBUOPOJS-UHFFFAOYSA-N Y InChI=1/C15H16N4.ClH/c1-9-6-13-15(8-11(9)16)18-14-7-10(19(2)3)4-5-12(14)17-13;/h4-8H,16H2,1-3H3;1H Key: PGSADBUBUOPOJS-UHFFFAOYAB
SMILES Cl.n1c3c(nc2c1cc(c(c2)N)C)cc(N(C)C)cc3
Properties
Chemical formula	C15H17N4
Molar mass	288.78 g/mol
Melting point	290 °C (554 °F; 563 K)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H315, H319, H335, H341
Precautionary statements	P201, P202, P261, P264, P270, P271, P280, P281, P301+P310, P302+P352, P304+P340, P305+P351+P338, P308+P313, P312, P321, P330, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Neutral red (pH indicator)
below pH 6.8		above pH 8.0
6.8	⇌	8.0

In microbiology, it is used in the MacConkey agar to differentiate bacteria for lactose fermentation.

Neutral red can be used as a vital stain.^[2] The Neutral Red Cytotoxicity Assay was first developed by Ellen Borenfreund in 1984. In the Neutral Red Assay live cells incorporate neutral red into their lysosomes. As cells begin to die, their ability to incorporate neutral red diminishes. Thus, loss of neutral red uptake corresponds to loss of cell viability.^[3] The neutral red is also used to stain cell cultures for plate titration of viruses.

Neutral red is added to some growth media for bacterial and cell cultures. It usually is available as a chloride salt.

Neutral red acts as a pH indicator, changing from red to yellow between pH 6.8 and 8.0.