electron microscopy (EM)

Classification

• EM techniques can be roughly divided into two main modalities which each require differently designed electron microscopes
  • transmission EM
    • an electron beam >= width of the field of view penetrates the sample
    • electrons transmitted through the sample create a projection image captured by a detector
    • samples are 100-300 nm, due to limited penetration depth of the electron beam
    • specimen is gradually tilted to generate a series of 2D projection images at different angles
      • these projections can be computationally aligned & combined into a tomographic volume
      • the tilt angle is restricted to a maximum of ~70 degrees
  • scanning EM
    • a focused electron beam scans the surface of the sample
    • backscattered electrons are collected by a detector situated above the sample
    • can be applied to larger specimens & larger fields of view than transmission EM
    • whole cells & specific areas in a cell may be analyzed
    • cryotomography is used to image the biological content in a near-native state
      • allows the direct visualization of macromolecular complexes like ribosomes & polysomes, clathrin coats, ATP synthases, & individual tubulin subunits in microtubules

Clinical significance

• resolution ~100 higher than light microscopy
• enables visualization of previously invisible virus particles

More general terms

• microscopy

More specific terms

• abnormal prion protein in brain by electron microscopy
• microscopic observation in stool by electron microscopy
• microscopic observation in tissue by electron microscopy
• platelet dense bodies in blood by electron microscopy