Cryo-electron microscopy (cryo-EM) is an imaging technique to visualize biomolecular structures, such as proteins, macromolecular complexes, bacteria and cell organelles with a subnanometer resolution.
Samples for cryo-EM are prepared by vitrification: cryo-fixation by rapid freezing. These frozen samples are then imaged in a near-native state at liquid nitrogen temperature. Because the samples are not chemically fixed or stained they can be imaged the highest resolution, but are also very sensitive to electron beam damage. Therefore pictures are taken at a very low electron dose and with the best imaging cameras, in order to prevent radiation damage and get a good signal.
Main techniques: SPA and tomography
In general, the contrast in typical cryo-EM images is still very low. Therefore, depending on the sample and the specific biological question, several post-data collection image processing methods are necessary to improve the signal-to-noise ratio and to reconstruct a 3D reconstruction from the 2D images. The two main techniques that are employed at NeCEN are Single Particle Analysis (SPA) and cryo-electron tomography (cryo-ET). By combining many (sometimes thousands of) noisy images, high resolution structural details can be obtained.
SPA and tomography allow scientists to zoom in on cells to the level of molecules and even atoms. The methods are suitable for a wide variety of research applications that can possibly lead to faster and better methods to understand, diagnose, cure and prevent diseases at a molecular level.