Inside Duke Medicine

Electron microscopy crew sweats the small things

For more than three decades, the Duke Electron Microscopy Service (DEMS) has played an important research and clinical role on campus and at the state and national levels. Today, it also stands ready to help defend against the threat of bioterrorism.

DEMS is the largest clinical virology electron microscopy (EM) laboratory in the U.S. – examining more than 1,000 specimens per year for evidence of viral infection – and is the country’s 2nd largest surgical pathology laboratory after the Mayo Clinic in Rochester, Minn.

Lab director Sara E. Miller, Ph.D., Professor of Pathology at the Duke University School of Medicine, co-teaches a national course in diagnostic virology at the CDC in Atlanta to help electron microscopists across the nation identify viruses, especially those that might be involved in bioterrorism. DEMS also has partnered with the North Carolina State Laboratory of Public Health to form the N.C. Laboratory Response Network.

“If North Carolina were to receive a potential viral sample that might be involved in bioterrorism or might cause an emerging disease for which we need a rapid diagnosis, our laboratory would be the EM laboratory involved,” Miller says.

Located in the Davison Building, DEMS is the oldest continuously running shared resource laboratory facility on campus, working with researchers and clinicians for more than 35 years. Miller and her staff of six highly skilled technologists have a combined nearly 200 years of experience in electron microscopy.

“DEMS is the only EM service facility on campus headed by a biological researcher knowledgeable of techniques available for analysis and who guides collaborators in methods for sample preparation and analysis of results,” Miller says.

Because electron microscopy can recognize unknown viruses in specimens quickly and without the use of molecular reagents such as antibodies or molecular probes, the technology is at the forefront of surveillance of emerging diseases and potential bioterrorism agents. For molecular tests requiring specific reagents, a guess has to be made about the potential pathogens that might be involved in order to choose the correct test. In the hands of experienced operators, however, EM can detect unusual organisms and disease processes without knowing beforehand what viral pathogens might be present for selection of the correct reagent.

In addition to viruses, DEMS analyzes cells and tissues, subcellular organelles, bacteria, fungi and parasites. At any one time, 15-20 research collaborations are in progress, and over the years, hundreds of researchers have availed themselves of the service. Its surgical pathology technologists not only prepare biopsy specimens, but also actually examine them in the microscopes and select the diagnostic areas for micrographs that the pathologists use in diagnosis, saving doctors valuable time. In many hospitals, the EM staff doesn’t have these skills, and the pathologists must operate the microscopes themselves to make their diagnoses.

“The value of the EM viral diagnostic laboratory lies in the rapidity of available results and the fact that no specific reagents are necessary,” Miller says. “The value of EM in the surgical pathology arena is that information on ultrasmall structures is available that is not possible to obtain from light microscopes.”

DEMS has three transmission electron microscopes (TEM) and one scanning electron microscope (SEM). The TEM looks at ultrathin slices of cells to see the subcellular structure inside samples, while the SEM generally looks at the outside of samples at the cellular level.

A TEM works like a light microscope in that a beam is “transmitted” through the specimen, but instead of photons (light), it uses electrons as the energy source. The image formed on a screen is a “shadow” of what’s in the way of the beam. For this to work, the sample must be very thin, either a tiny particle such as a virus sitting on a thin support film or a very thin slice of a cell or tissue stained and embedded in epoxy resin. A device called an ultramicrotome cuts sections 60-90 nanometers thick (a nanometer is a billionth of a meter) using a diamond knife. DEMS has six ultramicrotomes.

An SEM shoots an electron beam against a whole sample coated with a fine layer of evaporated metal, such as gold, so that electrons in the surface are bounced out of the specimen and monitored with an electronic detector. The detector or scintillator then amplifies and displays a topographical image on a cathode ray tube (CRT), much like a television or computer screen.

“EM provides rapid diagnosis for patients not available by other methods of analyses and without the use of specific reagents,” Miller says. “The DEMS is a specialty facility staffed by scientists knowledgeable in biological ultrastructure who have a collective experience in EM of close to two centuries helping others with fine structural investigations.”