Imaging of tissue sections with very slow electrons

Area of Science:

• Electron Microscopy
• Biological Imaging
• Materials Science

Background:

• Conventional electron microscopy of biological tissues yields low contrast due to light elements.
• Heavy metal staining enhances contrast but can alter or obscure cellular ultrastructure.
• High-energy electrons are typically used in transmission and scanning transmission electron microscopy.

Purpose of the Study:

• To develop a high-contrast imaging method for ultrathin biological samples without heavy metal staining.
• To investigate the use of low-energy electrons in scanning transmission electron microscopy (STEM) for enhanced contrast.
• To explore the potential of this technique for preserving native ultrastructural details.

Main Methods:

• Utilizing ultralow energy electrons (tens to hundreds of electronvolts) in STEM.
• Biasing thin tissue sections to a high negative potential to reduce electron energy.
• Employing ultrathin sections (<10nm thickness) and a grounded detector for transmitted electrons.

Main Results:

• Achieved extremely high contrast in ultrathin tissue sections without heavy metal staining.
• Observed detailed structures not enhanced by heavy atoms, preserving native ultrastructure.
• Demonstrated that slow electron bombardment depolymerizes embedding resin, enhancing signal without structural loss.

Conclusions:

• Ultralow energy STEM is a powerful tool for imaging unstained, ultrathin biological samples.
• This technique overcomes limitations of traditional heavy metal staining methods.
• The method shows promise for examining 2D crystals, polymer films, and other delicate materials.