Electron microscope sample

Samples prepared for electron microscopy reveal nanoscale details of biological structures, essential for cellular research.

About this subject

Electron microscopy enables visualization of biological structures at submicroscopic resolutions, reaching nanometer scales. Unlike optical microscopy, which uses light, electron microscopes use electron beams to generate images. There are two main types: transmission electron microscope (TEM) and scanning electron microscope (SEM). In TEM, electrons pass through ultrathin sections of the sample, revealing internal details like organelles and proteins. In SEM, the surface is scanned, producing three-dimensional topographic images.

Sample preparation for electron microscopy is a meticulous process. Biological tissues must be chemically fixed (e.g., with glutaraldehyde), dehydrated, and embedded in resins to enable extremely thin sections, with thicknesses of 50 to 100 nanometers. These sections are mounted on copper grids and contrasted with heavy metals like uranium and lead to enhance structural contrast. For SEM, samples are dehydrated and coated with a thin layer of gold or carbon to make them conductive.

The importance of electron microscopy in biology is invaluable. It enabled the discovery of DNA structure, visualization of viruses like HIV, and detailed study of cell organelles such as mitochondria and endoplasmic reticulum. Modern techniques like cryo-electron microscopy allow analysis of molecules in their native state by rapidly freezing them to preserve natural conformation. This technique earned the Nobel Prize in Chemistry in 2017 for Jacques Dubochet, Joachim Frank, and Richard Henderson.

Beyond biology, electron microscopy is used in materials science, geology, and nanotechnology. The magnification capability exceeds 2 million times, allowing observation of individual atoms in some cases.

Frequently Asked Questions

What is the difference between transmission electron microscope (TEM) and scanning electron microscope (SEM)?

TEM uses electrons that pass through the sample, revealing internal structure in thin sections. SEM scans the surface, generating three-dimensional topographic images.

Why do samples for electron microscopy need to be so thin?

For TEM, electrons must pass through the sample; thin sections (50-100 nm) allow electron transmission, avoiding excessive absorption and producing clear images.

What is cryo-electron microscopy and why is it important?

It is a technique that rapidly freezes samples at cryogenic temperatures, preserving native structure without chemical fixation. It allows studying molecules like proteins in near-native states, revolutionizing structural biology.