Microtome
A microtome is a mechanical instrument used to cut biological specimens into very thin segments for microscopic examination. Most microtomes use a steel blade and are used to prepare sections of animal or plant tissues for histology. The most common applications of microtomes are:
- Traditional histological technique: tissues are hardened by replacing water with paraffin. The tissue is then cut in the microtome at thicknesses varying from 2 to 25 µm (micrometers) thick. From there the tissue can be mounted on a microscope slide, stained and examined using a light microscope. See histology for more details.
- Cryosection: water-rich tissues are hardened by freezing and cut frozen; sections are stained and examined with a light microscope. This technique is much faster than traditional histology (5 minutes vs 16 hours) and are used in operations to achieve a quick diagnosis. Cryosections can also be used in immunohistochemistry as freezing tissue does not alter or mask its chemical composition as much as preserving it with a fixative.
- Electron microscopy: after embedding tissues in epoxy resin, a microtome equipped with a glass or diamond knife is used to cut very thin sections (typically 60 to 100 nanometers). Sections are stained and examined with a transmission electron microscope. This instrument is often called an ultramicrotome.
- Botanical microtomy: hard materials like wood, bone and leather require a sledge microtome. These microtomes have heavier blades and cannot cut as thin a regular microtomy.
Microtome blades are extremely sharp, and should be handled with great care. Safety precautions should be taken in order to avoid any contact with the cutting edge of the blade.
A recent development is the laser microtome, which cuts with a femtosecond laser instead of a mechanical knife. This method is contact-free and does not require sample preparation techniques. The laser microtome has the ability to slice almost every tissue in its native state. Depending on the material being processed, slice thicknesses of 10 to 100 µm are feasible.
See also