Epoxy resins are cut to what thickness on a microtome?

• A. 80-90 nm
• B. 0.5-1 µm
• C. 4-6 µm
• D. 1-2 µm

Answer: (A)

Ultrathin sections are needed for transmission electron microscopy because electrons must pass through the tissue to form an image. When epoxy resin–embedded blocks are cut on an ultramicrotome, the target thickness is on the order of tens of nanometers. A common and effective range is about 80–90 nanometers, which allows sufficient electron transmission while preserving ultrastructural detail. Thicker cuts, such as 0.5–1 µm or 1–2 µm, are used for light microscopy to survey the sample or for semi-thin sections, but they are too thick for TEM and would scatter electrons too much to produce a clear image.