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Electron Microscopy of Live Organisms
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Electron microscopes are powerful tools for studying small cells, viruses, and molecules within cells. An electron microscope can magnify an image up to 10 million times, allowing scientists to view objects on a smaller scale than with a conventional light microscope. Because the size of the electron is much smaller than the wavelength of visible light, electron microscopes have much greater resolving power than light microscopes. There are two major types of electron microscopes used by scientists. Transmission electron microscopy (TEM) allows for viewing of the internal structures of the specimen being studied. Scanning electron microscopy (SEM) permits viewing of the surface of the specimen, and can produce a three-dimensional image.

One major drawback to electron microscopy is that the process of preparing the specimen, as well as the actual process of examining the specimen, results in death of the cell or organism. Electron microscopes utilize a vacuum in order to allow the electrons to penetrate the specimen. Living organisms cannot survive in this vacuum, so all electron micrographs show only dead cells. These cells may even be distorted somewhat during the process of examination, due to the excessive processing needed to prepare the specimen, as well as the extremely low pressure environment of the microscope.

Researchers have recently noted that some small invertebrates are able to withstand being in a vacuum for short periods of times. Beetle larvae, ticks, and tardigrades (also called water bears) have all been previously shown to be able to withstand extremely low pressure environments. When these animals are observed using a scanning electron microscope, the electrons seemed to coat the animals, forming a protective barrier. Normally, when an animal, such as a small insect, is placed in a vacuum, they will dehydrate due to the low pressure and die. While the scanning electron microscope was being used, fruit fly larvae were able to survive up to one hour in the low pressure conditions. After being imaged, the larvae developed normally into adult fruit flies.

Fruit fly larvae are naturally coated with biological molecules. The researchers believed that the electron beams from the microscope caused the biological molecules to polymerize, or join together. These polymers were able to form a protective shield around the larvae. Other organisms that have a similar coating, such as a type of honeybee, required plasma irradiation to form the protective polymers. However, after being irradiated, these organisms were also able to survive the vacuum environment of the electron microscope. In order to confirm that the polymerized coating was indeed protecting these organisms in the vacuum, the researchers applied a similar artificial coating to animals that don’t naturally have one. After plasma irradiation, these organisms were also protected from the vacuum.

When the protected organisms were studied with the electron microscope, the structures of the organisms appeared quite different from traditionally prepared specimens. This might be because the polymer coating helped preserve the natural structure of the specimen. The environment of the electron microscope, as well as sample preparation, may cause distortions in the structure of the specimen. However, it is possible that since the researchers were using relatively low magnification settings, they obtained results that differed from prior, conventional electron microscopy examinations.

The data obtained, however, is interesting for a number of different reasons. First, it is encouraging to scientists trying to discover extraterrestrial life. If some small organisms from earth can survive in a vacuum with the protective polymer coating, it is possible that organisms from another world might also be able to survive using a similar mechanism. This would make it possible for the organism to be transported through the vacuum of outer space. In addition, this information might have result in big advancements for electron microscopy. Scientists may eventually be able to adapt the polymer coats to other organisms, or even single cells and viruses. This would permit the study of live organisms, and may even permit scientists to visualize specific interactions. For example, scientists could directly view a virus invading a host cell, and be able to figure out the process of infection. In addition, because traditional electron microscopy may result in distortion of the specimen, the protective coating may help scientists develop more accurate images.



References:

http://www.nature.com/news/nano-suit-shi...id-1.12799
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