Electron microscope sample

Samples for electron microscopy are prepared with precise techniques to reveal structures at the nanoscale, essential in biology and materials science.

About this subject

Samples for electron microscopy undergo rigorous preparation to withstand the vacuum and electron beam. In biology, tissues are fixed with glutaraldehyde, dehydrated in alcohol, and embedded in resin. Ultrathin sections (50-100 nm) are cut with an ultramicrotome and placed on copper grids. To prevent charge buildup, the sample is coated with a thin layer of gold or carbon, a process called sputter coating. For materials, solid samples need polishing or chemical etching to reveal grains and defects.

Electron microscopy has revolutionized science by enabling the visualization of viruses, cell organelles, and nanomaterials. The transmission electron microscope (TEM) uses electrons that pass through the sample, generating images with subnanometer resolution. The scanning electron microscope (SEM) scans the surface, producing high depth-of-field 3D images. Modern techniques include cryo-electron microscopy, which rapidly freezes samples to preserve native structures, awarded the Nobel Prize in Chemistry in 2017.

Interestingly, the first electron microscope image was taken in 1931 by Ernst Ruska and Max Knoll, showing a metal grid at 400x magnification. Today, resolution reaches 0.05 nm, enough to image individual atoms. In Brazil, institutions like LNLS and INMETRO maintain cutting-edge laboratories for research and innovation.

Frequently Asked Questions

How are biological samples prepared for electron microscopy?

Samples are chemically fixed, dehydrated, embedded in resin, and cut into ultrathin sections with an ultramicrotome. They are then mounted on grids and sputter-coated with gold or carbon to conduct electrons.

What is the difference between scanning and transmission electron microscopy?

Transmission electron microscopy (TEM) analyzes electrons that pass through the sample, revealing internal structure at very high resolution. Scanning electron microscopy (SEM) scans the surface, generating three-dimensional topographic images.

Why do samples need to be coated with metal?

Metal coating (gold or carbon) prevents electrical charge buildup on the sample surface, which would distort the electron beam and degrade the image. It also enhances secondary electron emission in SEM.