Electron microscope sample

Electron microscope samples reveal structures invisible to the naked eye, essential for advances in cellular and molecular biology.

About this subject

Electron microscope samples require special preparation to withstand the vacuum and electron beam, unlike optical microscopy samples. The process involves chemical fixation with glutaraldehyde, dehydration through graded alcohols, embedding in epoxy resin, and ultrathin sectioning with an ultramicrotome to obtain slices 50 to 100 nanometers thick. Heavy metals such as gold, platinum, or uranium are applied to enhance contrast and conductivity.

Preparation varies by sample type: biological (cells, tissues, viruses) or material (nanoparticles, metals, crystals). In biology, electron microscopy made it possible to visualize structures like ribosomes, mitochondria, and pathogenic viruses for the first time. The development of cryo-electron microscopy, which rapidly freezes the sample without crystallization, earned the 2017 Nobel Prize in Chemistry for Jacques Dubochet, Joachim Frank, and Richard Henderson.

In materials science, transmission electron microscopy (TEM) achieves atomic resolution, essential for characterizing nanomaterials and semiconductors. Scanning electron microscopy (SEM) produces three-dimensional surface images with depth of field far exceeding optical microscopes. Both require the sample to be conductive or to receive a metallic coating to dissipate electrical charge from the beam.

The aesthetic of the resulting images often intersects with art and design, inspiring textile patterns and visuals, but their primary role remains analytical and scientific. Each structural detail reveals information about composition, organization, and function of the observed materials or organisms.

Frequently Asked Questions

What is required to prepare a biological sample for electron microscopy?

The sample must be chemically fixed (e.g., glutaraldehyde), dehydrated, embedded in resin, cut into ultrathin slices (50, 100 nm), and stained with heavy metals like uranium or lead to enhance visibility.

What is the difference between scanning and transmission electron microscopy?

SEM scans the surface with an electron beam, producing three-dimensional topographic images. TEM transmits electrons through the sample, revealing internal structures such as cell organelles and even atoms.

Why do samples need to be conductive?

To prevent electrical charge buildup from the electron beam, which would distort the image. Non-conductive samples receive a coating of gold, platinum, or carbon.