Cryogenic electron microscopy

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

Scientists began developing cryo-EM in the 1970s. 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. This can lead to new medicines and treatments. In 2015, a science journal called Nature Methods named cryo-EM the "Method of the Year" for how much it changed science.

History

Cryogenic electron microscopy, or cryo-EM, started in the 1960s when scientists found that cooling samples could protect them from damage by strong electron beams. Early experiments used very cold liquids like liquid helium or liquid nitrogen, but these were hard to handle. By 1981, researchers used cryo-EM by freezing thin layers of water on special films. This let them 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 see very tiny things using a microscope. It makes the tiny things very cold. This helps scientists study small parts of living things, like proteins and other molecules.

Most of the time, this is done with a microscope that sends electrons through the sample. This is called transmission electron microscopy.

Scientists can take many pictures of a sample from different angles. They then combine these pictures to make a 3D model. This helps them see very small details, almost as small as atoms.

Cryo-EM has become very popular. It doesn’t need the sample to be turned into a crystal. This is different from another method called X-ray crystallography. This makes it easier to study many different kinds of molecules.

Specimen handling for imaging

Biological specimens are placed on a special grid and frozen very quickly in liquid ethane. This keeps them in their natural state and protects them from damage when viewed under a powerful microscope. Because these tiny samples are delicate, special care is taken to get clear pictures without harming them.

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

Image processing in cryo-TEM

In cryo-TEM, making the clearest picture isn’t always the main goal. One big challenge is noise, which can make images blurry. Scientists use special math methods to sort out the shapes and positions of tiny particles.

Two main methods are used today. The maximum likelihood estimation approach looks at all possible positions of particles. The Bayesian approach uses the original data to improve the image and reduce noise. These methods help scientists create better images of very small structures. The software program RELION has made these methods easier to use.