Osmium tetroxide, 4% solution is a microfiltered aqueous OsO4 reagent used for post-fixation and staining in electron microscopy. Osmium tetroxide reacts with tissue components, particularly unsaturated lipids, supporting membrane preservation and electron contrast during ultrastructural specimen preparation.
Synonyms: Osmium tetroxide solution; OsO4; osmic acid solution.
The 4% aqueous solution is supplied in pre-scored sealed ampoules, with an ampoule cracker provided for each ampoule. This format provides a prepared concentration for electron microscopy workflows and can be diluted with an appropriate buffer when lower osmium tetroxide concentrations are required.
Osmium tetroxide is also used after DAB/peroxidase reactions to increase the electron density and contrast of the deposited reaction product for electron microscopic localization.
Key Properties
- 4% aqueous osmium tetroxide (OsO4) solution
- Microfiltered for electron microscopy specimen preparation
- Used for post-fixation and electron-dense staining
- Reacts preferentially with unsaturated lipid components in biological specimens
- Supplied in pre-scored sealed ampoules with ampoule crackers
- CAS number: 20816-12-0
- Available as 20 × 2 mL (0972A), 5 × 10 mL (0972B), and 20 × 10 mL (0972C)
Applications
Electron Microscopy Post-Fixation
Osmium tetroxide is widely used as a secondary fixative following aldehyde fixation in transmission electron microscopy specimen preparation. Its reaction with lipid-rich structures contributes to preservation and visualization of cellular membranes and other ultrastructural features.
Membrane & Lipid Contrast
OsO4 reacts with unsaturated lipid components and deposits electron-dense osmium within treated specimens. This chemistry contributes contrast to membrane-rich and lipid-containing structures during electron microscopy.
DAB/Peroxidase Contrast Enhancement
Osmium tetroxide can be used after diaminobenzidine (DAB)/peroxidase reactions to increase the electron density of the reaction deposit, supporting localization of peroxidase activity by electron microscopy.
Buffered Fixative Preparation
The 4% aqueous solution can be combined with an appropriate buffer to prepare lower-concentration osmium tetroxide fixatives. The 4% stock may be diluted to 2% or 1% according to the requirements of the validated specimen-preparation protocol. Researchers who prefer a prepared lower concentration can select Osmium tetroxide, 2% solution.
Compatibility & Bonding Considerations
- Can be diluted with appropriate buffer systems to prepare lower OsO4 concentrations
- Aqueous osmium tetroxide solutions are hypotonic; buffer and osmolarity should be selected for the specimen and fixation protocol
- Commonly used after primary aldehyde fixation in electron microscopy workflows
- Fixation time, concentration, temperature, buffer composition, and specimen dimensions influence osmium penetration and staining
Keep fixation and processing conditions consistent when comparing specimens. Users requiring a prepared lower concentration may select Osmium tetroxide, 2% solution. For preparation of laboratory-defined concentrations, Osmium tetroxide, crystalline, ≥99.95% is also available.
Application Tips
- Dilute the 4% aqueous solution with the selected buffer when a lower working concentration is required
- Keep fixation concentration, buffer composition, temperature, and exposure time consistent between comparative specimens
- Use clean glassware and handling techniques that minimize contamination of osmium tetroxide solutions
- Keep prepared solutions tightly closed and cold when they are not being actively used
- Select fixation conditions according to specimen type, dimensions, and the validated electron microscopy protocol
For additional information on osmium tetroxide properties, solution preparation, dilution, packaging, and handling, refer to the Osmium Tetroxide Technical Data Sheet (TDS).
Handling & Storage
- Store at 4°C with the container tightly closed
- Keep cold and protected from unnecessary light exposure
- Handle only with appropriate laboratory ventilation or in a chemical fume hood
- Wear appropriate protective gloves, chemical splash goggles, and protective clothing
- Avoid inhalation of osmium tetroxide vapor and contact with skin or eyes
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FAQ
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1. What is osmium tetroxide used for?
Osmium tetroxide is used as a post-fixative and electron-dense stain in electron microscopy. Its reaction with unsaturated lipid components helps preserve and provide contrast to cellular membranes and other lipid-containing structures.
2. Why is osmium tetroxide used in electron microscopy?
Osmium tetroxide reacts with tissue components, particularly unsaturated lipids, and introduces electron-dense osmium into the specimen. This contributes to membrane preservation and contrast in electron microscopy preparations.
3. Can the 4% osmium tetroxide solution be diluted?
Yes. The 4% aqueous solution can be diluted with an appropriate buffer to prepare lower concentrations such as 2% or 1%, depending on the specimen and validated fixation procedure. A ready-to-use lower-concentration option is available as Osmium tetroxide, 2% solution. See the Technical Data Sheet (TDS) for additional preparation information.
4. What package sizes are available for the 4% solution?
The 4% solution is available as 20 × 2 mL ampoules (0972A), 5 × 10 mL ampoules (0972B), and 20 × 10 mL ampoules (0972C). Current pricing varies by package configuration. For larger quantity requirements, request a bulk quote.
5. Where can I find the SDS for Osmium Tetroxide, 4% Solution?
Safety Data Sheets are available for each package configuration: 0972A, 20 × 2 mL SDS, 0972B, 5 × 10 mL SDS, and 0972C, 20 × 10 mL SDS.
Safety & Documentation
Osmium tetroxide is highly hazardous and volatile. The 4% solution is classified as fatal in contact with skin, toxic if inhaled, and capable of causing severe skin burns and serious eye damage. Handle in a chemical fume hood with appropriate gloves, chemical eye protection, and protective clothing. Review the appropriate 0972A Safety Data Sheet (SDS), 0972B Safety Data Sheet (SDS), or 0972C Safety Data Sheet (SDS) for package-specific safety information. Consult the Osmium Tetroxide Technical Data Sheet (TDS) for preparation, dilution, packaging, and handling guidance.
