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Toluidine blue, also known as TBO or tolonium chloride ( INN) is a blue cationic (basic) dye used in
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mol ...
and sometimes clinically.


Test for lignin

Toluidine blue
solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry, a solution is a special type of Homogeneous and ...
is used in testing for
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood Wood is a porous and fibrous s ...

lignin
, a complex
organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, catenate (form chains with other carbon ...
that bonds to
cellulose Cellulose is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, cate ...
fibres and strengthens and hardens the
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
s in
plants Plants are mainly multicellular organisms, predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiratio ...
. A positive toluidine blue test causes the
solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water the solvent. In chemistry, a solution is a special type of Homogeneous and ...
to turn from
blue Blue is one of the three primary color, primary colours of pigments in painting and traditional colour theory, as well as in the RGB color model, RGB colour model. It lies between Violet (color), violet and green on the optical spectrum, spectr ...
to
pink Pink is a pale tint of red that is named after a flower of the same name. It was first used as a color name in the late 17th century. According to surveys in Europe and the United States, pink is the color most often associated with charm, polit ...
. A similar test can be performed with phloroglucinol- HCl solution, which turns red.


Other histological uses

Toluidine blue is often used to identify
mast cell A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...
s, by virtue of the
heparin Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. As a medication it is used as an anticoagulant Anticoagulants, commonly known as blood thinners, are chemical substance A chemic ...
in their cytoplasmic granules. It is also used to stain
proteoglycans Proteoglycans are protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including E ...
and
glycosaminoglycans . For polysaccharide nomenclature see here. R1, R2, R3 may have different values. Image:Hyaluronan.svg, 240px, Hyaluronic acid, Hyaluronan (-4GlcUA''β''1-3GlcNAc''β''1-)n Glycosaminoglycans (GAGs) or mucopolysaccharides are long linear polysac ...

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.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 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 mucous membrane, mucosal dysplasia (which preferentially take up the dye compared to normal tissue) in premalignant lesions (e.g. leukoplakia). 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

{{reflist * 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. Phenothiazines Thiazine dyes Chlorides