Ultramicrotomy

Ultramicrotomy is a method for cutting specimens into extremely thin slices, called ultra-thin sections, that can be studied and documented at different magnifications in a transmission electron microscope (TEM). It is used mostly for biological specimens, but sections of plastics and soft metals can also be prepared. Sections must be very thin because the 50 to 125 kV electrons of the standard electron microscope cannot pass through biological material much thicker than 150 nm. For best resolutions, sections should be from 30 to 60 nm. This is roughly the equivalent to splitting a 0.1 mm-thick human hair into 2,000 slices along its diameter, or cutting a single red blood cell into 100 slices.

Ultramicrotomy process

There are numerous pieces of equipment involved in the ultramicrotomy process. "Thin" sections, meaning sections from 50 to 100 nm thick, are able to be viewed in the TEM. Semithin or "thick" sections range from 0.5 to 2 µm, and are almost 10 to 20 times thicker than "thin" sections. These thick sections are also known as survey sections and are viewed in a light microscope to determine whether the right area of the specimen is in a position for thin sectioning. It is therefore a very common practice to view thick sections in a light microscope first, before proceeding with ultramicrotomy or thin sectioning.