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Tuesday, May 11, 2010

Seeing atoms


Hong Zhou and his team from UCLA have succeeded in ‘seeing’ atoms, using a new type of microscope. For the first time, biological complexes were visualized at the atomic level.

The cryo-electron microscope is capable of displaying objects only a few angstroms (10-10 meters) across. You can get an idea of how small this is from the diagram of the water molecule shown below. 95 pm (picometers) equals 0.95 angstrom. Visible light falls between 4000 and 7000 angstroms. Anything smaller than that will not diffract visible light and so cannot be seen with a traditional light microscope.

Electron microscopes repeatedly fire beams of electrons at a sample from various angles. The path of the electrons is read by a digital camera and reconstructed into a 3D image. Where light microscopes can magnify objects up to 2000x, an electron microscope has a magnification cabability of up to one million times.

Cryo-elecron microscopy, like other types of electron microscopy (EM), can visualize objects only a few angstroms across. However, unlike most types of EM, the samples do not have to be specially stained or prepared. Instead, the samples are flash frozen, usually in liquid nitrogen. This means that biological samples can be viewed exactly as they were in their native environments. For example, Zhou and his colleagues used cryo-electron microscopy to watch the process of cell infection by a virus, a process that until now has been poorly understood. They were able to see viral structures that were only 3.3 angstroms across.