Toluidine blue

Toluidine blue, also known as TBO or tolonium chloride (INN) is a blue cationic (basic) dye used in histology and sometimes clinically.

Toluidine blue

Names
IUPAC name (7-amino-8-methylphenothiazin-3-ylidene)-dimethylammonium chloride
Other names Toluidine blue O
Identifiers
CAS Number	92-31-9
3D model (JSmol)	Interactive image
ChEBI	CHEBI:87647
ChEMBL	ChEMBL1790006
ChemSpider	11239098
ECHA InfoCard	100.001.952
MeSH	Tolonium+chloride
PubChem CID	7084
UNII	15XUH0X66N
CompTox Dashboard (EPA)	DTXSID9048728
InChI InChI=1S/C15H16N3S.ClH/c1-9-6-13-15(8-11(9)16)19-14-7-10(18(2)3)4-5-12(14)17-13;/h4-8H,16H2,1-3H3;1H/q+1;/p-1 Key: HNONEKILPDHFOL-UHFFFAOYSA-M InChI=1/C15H16N3S.ClH/c1-9-6-13-15(8-11(9)16)19-14-7-10(18(2)3)4-5-12(14)17-13;/h4-8H,16H2,1-3H3;1H/q+1;/p-1 Key: HNONEKILPDHFOL-REWHXWOFAY
SMILES [Cl-].CN(C)c1ccc2nc3cc(C)c(N)cc3[s+]c2c1
Properties
Chemical formula	C15H16N3S^+
Molar mass	270.374 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Test for lignin

Toluidine blue solution is used in testing for lignin, a complex organic molecule that bonds to cellulose fibres and strengthens and hardens the cell walls in plants. A positive toluidine blue test causes the solution to turn from blue to pink. A similar test can be performed with phloroglucinol-HCl solution, which turns red.

Other histological uses

Toluidine blue is often used to identify mast cells, by virtue of the heparin in their cytoplasmic granules.[1] It is also used to stain proteoglycans and glycosaminoglycans in tissues such as cartilage. The strongly acidic macromolecular carbohydrates of mast cells and cartilage are coloured red by the blue dye, a phenomenon called metachromasia.

Alkaline solutions of toluidine blue are commonly used for staining semi-thin (0.5 to 1 μm) sections of resin-embedded tissue. At high pH (about 10) the dye binds to nucleic acids and all proteins. Although everything in the tissue is stained, structural details are clearly visible because of the thinness of the sections. Semi-thin sections are used in conjunction with ultra-thin sections examined by electron microscopy.

Toluidine blue is also commonly used to stain frozen sections (rapid microscopic analysis of a specimen). Because time is of the essence for a frozen section, toluidine blue allows for the frozen section to be stained and reviewed in 10-20 seconds.[2] The other staining method for frozen sections (rapid H&E) takes approximately 60 to 90 seconds.

Clinical uses

The dye is sometimes used by surgeons to help highlight areas of mucosal dysplasia (which preferentially take up the dye compared to normal tissue) in premalignant lesions (e.g. leukoplakia).[3] This can be used to choose the best site of the lesion to biopsy, or during surgery to remove the lesion to decide whether to remove more tissue from the margins of the excision defect or leave it behind.

References

1. Carson, Freida L; Hladik, Christa (2009). Histotechnology: A Self-Instructional Text (3 ed.). Hong Kong: American Society for Clinical Pathology Press. p. 188. ISBN 978-0-89189-581-7.
2. Sridharan G, Shankar A. "Toluidine blue: A review of its chemistry and clinical utility. J Oral Maxillofac Pathol. 2012 May-Aug; 16(2):251-255
3. Scully, C; Porter, S (Jul 22, 2000). "ABC of oral health. Swellings and red, white, and pigmented lesions". BMJ (Clinical research ed.). 321 (7255): 225–8. doi:10.1136/bmj.321.7255.225. PMC 1118223. PMID 10903660.

• Carson FL (1997) Histotechnology. A Self-Instructional Text. 2nd ed. American Society of Clinical Pathologists, Chicago.
• Green FJ (1990) The Sigma-Aldrich Handbook of Stains, Dyes and Indicators. Aldrich Chemical Company, Milwaukee, Wisconsin.
• Horobin RW, Kiernan JA, Eds (2002) Conn's Biological Stains. A Handbook of Dyes, Stains and Fluorochromes for Use in Biology and Medicine. 10th ed. BIOS, Oxford.
• Kiernan JA (2008) Histological and Histochemical Methods: Theory and Practice. 4th ed. Scion, Bloxham, UK.