Cryo electron microscopy is a structural biology technique that images biomolecules in a near native, frozen hydrated state. Samples such as proteins, nucleic acids and large complexes are rapidly vitrified in a thin layer of amorphous ice, preserving their structure without chemical fixation or staining. An electron beam then passes through the sample and a highly sensitive detector records many low dose images to limit radiation damage.

The core approach in single particle cryo electron microscopy is to image tens of thousands to millions of identical particles in random orientations. Computational image processing aligns and classifies these two dimensional projections and reconstructs a three dimensional density map. Improvements in direct electron detectors, motion correction algorithms and contrast transfer function refinement have pushed achievable resolutions into the near atomic range, allowing side chains and even bound water molecules to be visualized in favorable cases.

Cryo electron microscopy has been particularly powerful for large, dynamic or membrane associated complexes that are difficult to crystallize. It has revealed the structures and functional motions of ion channels, rotary ATPases, ribosomes, viruses and many other macromolecular machines. Time resolved and in situ approaches are extending the method to capture transient states and visualize structures inside cells. Continued advances in microscope optics, phase plates, automation, and artificial intelligence based image processing are expected to further improve resolution, throughput and accessibility. Overall, cryo electron microscopy has become a central tool for understanding molecular mechanisms at high resolution and for guiding drug discovery by revealing biologically relevant conformations and interaction sites.