Electron microscope sample

Samples for electron microscopy are prepared using rigorous techniques to reveal cellular and molecular structures at the nanoscale.

About this subject

Electron microscopy is a fundamental tool in modern biology, enabling visualization of structures ranging from cellular organelles to viruses and macromolecules. For a sample to be observed in a scanning electron microscope (SEM) or transmission electron microscope (TEM), it must undergo a meticulous preparation process. This includes chemical fixation to preserve structure, dehydration, embedding in resins, ultrathin sectioning with an ultramicrotome, and, for SEM, coating with gold or carbon to make the surface conductive. Each step is critical to avoid artifacts and ensure the resulting image faithfully represents the original morphology. In Brazil, electron microscopy laboratories are present at universities such as USP, Unicamp, and UFRJ, as well as research centers like LNLS (National Synchrotron Light Laboratory). The technique has revolutionized fields such as virology, where it enabled the first observation of viral particles like HIV, and neurobiology, with three-dimensional reconstruction of synapses. Interestingly, sample preparation for electron microscopy can take days or even weeks, depending on the complexity and type of analysis required.

Frequently Asked Questions

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

In SEM, an electron beam scans the sample surface, producing three-dimensional images of topography. In TEM, electrons pass through the sample, generating two-dimensional images of internal structures with atomic resolution.

Why do samples need to be coated with metal for SEM?

Metal coating with gold or carbon makes the sample surface conductive, preventing charge buildup that would distort the image. It also enhances secondary electron emission, improving contrast.

How long does it take to prepare a sample for electron microscopy?

The process can take from a few hours to several weeks, depending on sample complexity. Biological tissues require fixation, dehydration, resin embedding, and ultrathin sectioning, each time-consuming step.