Editing Osmium tetroxide (section)

===Biological staining===


OsO<sub>4</sub> is a widely used [[staining]] agent used in [[transmission electron microscopy]] (TEM) to provide contrast to the image.<ref name="Bozzola">{{ cite book |author1=Bozzola, J. J. |author2=Russell, L. D. | chapter = Specimen Preparation for Transmission Electron Microscopy | title = Electron Microscopy: Principles and Techniques for Biologists | year = 1999 | publisher = Jones and Bartlett | location = Sudbury, MA | pages = 21–31 | isbn = 978-0-7637-0192-5 | chapter-url = https://books.google.com/books?id=RqSMzR-IXk0C&pg=PA21 }}</ref> This staining method may also be known in the literature as the OTO<ref>{{Cite journal|last1=Seligman|first1=Arnold M.|last2=Wasserkrug|first2=Hannah L.|last3=Hanker|first3=Jacob S.|title=A new staining method (OTO) for enhancing contrast of lipid--containing membranes and droplets in osmium tetroxide--fixed tissue with osmiophilic thiocarbohydrazide(TCH)|date=1966-08-01|journal=The Journal of Cell Biology|volume=30|issue=2|pages=424–432|doi=10.1083/jcb.30.2.424|issn=0021-9525|pmc=2106998|pmid=4165523}}</ref><ref>{{Citation |last1=Unger |first1=Ann-Katrin |date=2020 |work=Volume Microscopy : Multiscale Imaging with Photons, Electrons, and Ions |pages=165–178 |editor-last=Wacker |editor-first=Irene |place=New York, NY |publisher=Springer US |language=en |doi=10.1007/978-1-0716-0691-9_9 |isbn=978-1-0716-0691-9 |last2=Neujahr |first2=Ralph |last3=Hawes |first3=Chris |last4=Hummel |first4=Eric |title=Improving Serial Block Face SEM by Focal Charge Compensation |series=Neuromethods |volume=155 |s2cid=226563386 |editor2-last=Hummel |editor2-first=Eric |editor3-last=Burgold |editor3-first=Steffen |editor4-last=Schröder |editor4-first=Rasmus}}</ref> (osmium-thiocarbohydrazide-osmium) method, or osmium impregnation<ref>{{Cite journal|last1=Tapia|first1=Juan C.|last2=Kasthuri|first2=Narayanan|last3=Hayworth|first3=Kenneth|last4=Schalek|first4=Richard|last5=Lichtman|first5=Jeff W.|last6=Smith|first6=Stephen J|last7=Buchanan|first7=JoAnn|date=2012-01-12|title=High contrast en bloc staining of neuronal tissue for field emission scanning electron microscopy|journal=Nature Protocols|volume=7|issue=2|pages=193–206|doi=10.1038/nprot.2011.439|issn=1754-2189|pmc=3701260|pmid=22240582}}</ref> technique or simply as osmium staining. As a [[lipid]] stain, it is also useful in [[scanning electron microscopy]] (SEM) as an alternative to [[sputter coating]]. It embeds a heavy metal directly into cell membranes, creating a high electron scattering rate without the need for coating the membrane with a layer of metal, which can obscure details of the cell membrane. In the staining of the [[plasma membrane]], osmium(VIII) oxide binds [[phospholipid]] head regions, thus creating contrast with the neighbouring [[protoplasm]] (cytoplasm). Additionally, osmium(VIII) oxide is also used for fixing biological samples in conjunction with HgCl<sub>2</sub>. Its rapid killing abilities are used to quickly kill live specimens such as protozoa. OsO<sub>4</sub> stabilizes many proteins by transforming them into gels without destroying structural features. Tissue proteins that are stabilized by OsO<sub>4</sub> are not coagulated by alcohols during dehydration.<ref name=stain>{{ cite book | author = Hayat, M. A. | title = Principles and Techniques of Electron Microscopy: Biological Applications | publisher = Cambridge University Press | year = 2000 | pages = 45–61 | isbn = 0-521-63287-0 | url = https://books.google.com/books?id=nfsVMH8it1kC }}</ref> Osmium(VIII) oxide is also used as a stain for lipids in optical microscopy.<ref>{{ cite journal | title = A simple protocol for paraffin-embedded myelin sheath staining with osmium(VIII) oxide for light microscope observation |author1=Di Scipio, F. |author2=Raimondo, S. |author3=Tos, P. |author4=Geuna, S. | journal = Microscopy Research and Technique | year = 2008 | volume = 71 | issue = 7 | pages = 497–502 | doi = 10.1002/jemt.20577 | pmid = 18320578 |s2cid=9404999 }}</ref> OsO<sub>4</sub> also stains the human cornea (see [[Osmium tetroxide#Safety considerations|safety considerations]]).

[[File:Resin-Embedded Transmission Electron Microscope Sample.jpg|thumb|left|A sample of cells fixed/stained with osmium tetroxide (black) embedded in epoxy resin (amber). The cells are black as a result of the effects of osmium tetroxide.]]