Tolonium chloride

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Tolonium chloride
Tolonium chloride.svg
IUPAC name
(7-amino-8-methyl- phenothiazin-3-ylidene)- dimethyl-ammonium
Other names
Toluidine blue O
3D model (JSmol)
ECHA InfoCard 100.001.952
MeSH Tolonium+chloride
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

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

Test for lignin[edit]

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[edit]

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.

Clinical uses[edit]

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).[2] 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.


  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. ^ 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.