Cryo electron microscopy is a structural biology technique that images biological molecules in a frozen, near native state. Samples such as proteins, nucleic acids or large molecular assemblies are rapidly vitrified to prevent ice crystal formation, preserving their natural shapes. An electron beam is then passed through these thin, frozen specimens in a transmission electron microscope, and the resulting images are computationally processed to reconstruct three dimensional structures.

The method overcomes several limitations of classic structural techniques. Unlike X ray crystallography, it does not require crystals, which are difficult or impossible to grow for many flexible or large complexes such as membrane proteins, ribosomes or viral particles. Compared to conventional electron microscopy with heavy metal stains or dehydration, vitrification maintains hydration and avoids major distortions. Modern direct electron detectors and advanced image processing have pushed resolution into the near atomic range, making it possible to visualize side chains, bound ligands and subtle conformational changes.

Researchers can use single particle analysis to align thousands to millions of noisy particle images and obtain high resolution reconstructions of heterogeneous populations, revealing multiple functional states. Tomography allows three dimensional imaging of thicker samples, including sections of cells, showing macromolecular complexes in situ. These capabilities have transformed drug discovery, enabling mapping of drug binding sites and rational design of inhibitors against targets such as ion channels, viral proteins or enzymes.

Ongoing research focuses on improving detectors, phase plates and data processing algorithms to increase resolution, reduce required sample quantities and better resolve dynamic or disordered regions. Together, these advances make cryo electron microscopy a central tool for understanding biological function at the molecular level.