Electron microscope sample

Electron microscopes achieve magnifications up to 10 million times, revealing details of cells and viruses invisible to light microscopes.

About this subject

The electron microscope is a powerful tool that uses beams of electrons instead of light to visualize extremely small structures. Unlike optical microscopes, whose resolution limit is about 200 nanometers due to the wavelength of light, electron microscopes can resolve details down to 0.05 nanometers. This is possible because electrons have much shorter wavelengths, on the order of picometers, enabling magnifications that exceed 10 million times.

There are two main types: transmission electron microscope (TEM) and scanning electron microscope (SEM). In TEM, electrons pass through an ultrathin sample, forming an image based on the material's electron density. SEM scans the sample's surface with a focused beam, generating high-resolution three-dimensional images. Both require meticulous sample preparation, including dehydration, fixation, and often coating with conductive metals to prevent charge buildup.

Sample preparation for electron microscopy is a critical step. Biological tissues must be fixed with glutaraldehyde, dehydrated through ethanol series, and embedded in resins for ultrathin sectioning. For inorganic materials such as catalysts or nanoparticles, dispersion in solvents and deposition on copper grids is common. Advanced techniques like cryo-electron microscopy rapidly freeze samples in liquid nitrogen, preserving their native structure without chemical fixation.

This technology has revolutionized science by visualizing structures such as porin complexes in bacterial membranes, the capsid of viruses like SARS-CoV-2, and even individual atoms in crystals. In Brazil, institutions like the National Nanotechnology Laboratory (LNNano) in Campinas operate state-of-the-art electron microscopes open to the scientific community, driving research in materials, biology, and medicine.

Frequently Asked Questions

What is the difference between a transmission electron microscope and a scanning electron microscope?

TEM (transmission) uses electrons that pass through the sample, generating 2D images of internal structures. SEM (scanning) scans the surface with a beam, producing 3D topographical images.

Why do samples need to be coated with metal for scanning electron microscopy?

The metal coating (gold, platinum, or carbon) makes the sample conductive, preventing charge accumulation that would distort the image. It also improves secondary electron emission for better contrast.

What are the medical applications of electron microscopy?

It enables diagnosis of viral diseases by observing virus particles, studying cellular structures in pathologies like cancer, and analyzing biomaterials for implants. Cryo-electron microscopy is especially crucial for vaccine and drug development.