A Primer on Electron Microscopy

May 28, 2013

(Español) When Robert Gallo first observed the structure of retroviruses in 1975 and later identified the HIV retrovirus, he used an electron microscope (EM).  When Luc Montagnier accepted the Nobel Prize in 2008, he used Gallo’s EM photographs to describe the structure of HIV. File:Electron Microscope.pngIn the field of virology, no device has been more important than the electron microscope (EM).  First developed during the 1930s, EM continues to be used in the discovery and description of viruses:

EM allows an “open view” of whatever might be present, while molecular tests require knowledge about the potential agent(s) to determine the correct test(s). EM, though it may not be able to identify a virus beyond the family level, at least points the way for more specific identification by other methods such as biochemical assays for specific pathogens… in cases of dual infections, molecular or antigen-based testing would likely miss the second agent.

HOW IT WORKS (from Wikipedia) An electron microscope (EM) uses an electron beam to illuminate a specimen and produce a magnified image.  It has greater resolving power than light microscopes and can reveal the structure of smaller objects because electrons have wavelengths about 100,000 times shorter than visible light photons.  They can achieve better than 50 pm resolution and magnifications of up to about 10,000,000x whereas ordinary, non-confocal light microscopes are limited by diffraction to about 200nm resolution and useful magnifications below 2000x. The electron microscope uses electrostatic and electromagnetic lenses to control the electron beam and focus it to form an image. These electron optical lenses are analogous to the glass lenses of a light optical microscope. Hans Gelderblom explains how electron microscopes are used to detect HIV (Courtesy House of Numbers [2009]:

Electron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens including microorganisms, cells, large molecules, biopsy samples, metals, and crystals.  Industrially, the electron microscope is often used for quality control and failure analysis.  Modern electron microscopes produce electron micrographs, using specialized digital cameras or frame grabbers to capture the image. Law enforcement agencies and private investigators have been using scientific tools like EM to collect and record forensic evidence for decades.  Technologies like gas chromatography, RADAR and LASER are routinely used by investigators to detect, identify, measure, observe, and record substances, objects and velocities.  While organizations like the College of American Pathologists (CAP), the Clinical Laboratory Improvement Amendments (CLIA) and the Clinical Laboratory Improvement Program (CLIP) regulate and certify laboratories involved in the diagnosis and treatment of patients, criminal investigators are under no such restrictions.

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