Cryogenic electron microscopy

Cryogenic electron microscopy, or cryo-EM, is a special way scientists use to see really tiny parts of living things. It uses a type of microscope called a transmission electron microscope, but the samples are kept very cold, almost frozen, to keep their natural shape. This helps scientists look at molecules and other tiny structures in great detail.

Scientists started developing cryo-EM in the 1970s, and with new technology, they can now see these structures almost at the level of atoms. This makes cryo-EM a great tool for studying things that are hard to look at with other methods, like X-ray crystallography or NMR spectroscopy.

To prepare samples for cryo-EM, scientists put the material they want to study into a special kind of ice called vitreous ice. They do this by dropping the sample onto a grid and then freezing it quickly in liquid ethane or a mix of ethane and propane. This keeps the sample safe and unchanged for viewing.

In 2017, three scientists—Jacques Dubochet, Joachim Frank, and Richard Henderson—won the Nobel Prize in Chemistry for creating and improving cryo-EM. Their work helps us understand how important molecules work in our bodies, which can lead to new medicines and treatments. In 2015, a science journal called Nature Methods even named cryo-EM the "Method of the Year" for how much it changed science.

History

Cryogenic electron microscopy, or cryo-EM, began in the 1960s when scientists realized that cooling samples could protect them from damage caused by strong electron beams. Early experiments used very cold liquids like liquid helium or liquid nitrogen, but these were difficult to manage. By 1981, researchers successfully used cryo-EM by freezing thin layers of water on special films, which allowed them to study tiny structures like viruses.

In the 2010s, new cameras called direct electron detectors and better computer programs made it possible to see structures almost at the level of individual atoms. This helped scientists study important molecules such as ribosomes and ion channels. In 2017, three scientists won the Nobel Prize in Chemistry for their work that made cryo-EM a powerful tool in biology. Today, cryo-EM is widely used in labs around the world to explore the shapes of proteins and other tiny structures.

Main article: Nobel Prize in Chemistry

Techniques

Main article: Transmission electron cryomicroscopy

Main article: Correlative light-electron microscopy

Main article: Scanning electron cryomicroscopy

Main article: Electron cryotomography

Main article: Single particle analysis

Main article: Electron crystallography

Cryogenic electron microscopy (cryo-EM) is a special way to look at tiny things using a microscope that makes them cold. It helps scientists study how tiny parts of living things are built, like proteins and other molecules. Most of the time, this is done using a type of microscope that sends electrons through the sample, called transmission electron microscopy.

Scientists can take many pictures of a sample from different angles and combine them to make a 3D model. This helps them see very small details, almost as small as atoms. Cryo-EM has become very popular because it doesn’t need the sample to be turned into a crystal, unlike another method called X-ray crystallography. This makes it easier to study many different kinds of molecules.

Specimen handling for imaging

Biological specimens are prepared by spreading them on a special grid and freezing them very quickly in liquid ethane to keep them in a natural state. This helps protect them from damage when they are looked at under a powerful microscope. Because these tiny samples are very delicate, special care is taken to get clear pictures without harming them.

This method can also be used for studying materials that would normally disappear or change when looked at with regular microscopes. For example, certain liquids or gases can be frozen and examined safely, allowing scientists to see details that were impossible before.

Image processing in cryo-TEM

In cryo-TEM, getting the clearest picture isn’t always the main goal. One big challenge is dealing with noise, which can make the image blurry. Scientists use special math methods to help sort out the different shapes and positions of tiny particles in the sample.

Two main methods are used today. The maximum likelihood estimation approach, which started being used in 1998, looks at all possible positions of particles to figure out the most likely arrangement. The Bayesian approach uses the original data to improve the image and reduce noise, making the results more reliable. These methods help scientists create better images of very small structures. The software program RELION has made these methods easier to use, helping researchers improve their results.