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The magnifying powers of a scanning electron microscope (SEM) can make a blood clot look like a traffic jam or turn a simple dust bunny into a jungle of seemingly massive threads. The technology, which employs electrons instead of light to scan surfaces, exposes samples to a harsh vacuum. Because water becomes unstable under these conditions, drying processes were developed to retain key structural elements of hydrated samples, such as cells and tissue. It would be preferable to observe the samples in their original state, however. Findings published online today by the Proceedings of the National Academy of Sciences point to a novel way of doing just that.
Stephan Thiberge of the Weizmann Institute of Science in Israel and his colleagues developed the wet-SEM method. To protect the water in the biological samples from boiling explosively under the vacuum, the researchers encased the samples in a thin polymer membrane. This "wet suit" is invisible to the electron beam but is tough enough to withstand atmospheric pressure differences and protect its contents. The new setup provides advantages over standard SEM, the researchers report. One, they state, is that "SEM can now be used to probe the inside of whole cells, giving information on organelles and internal structure." (The image above is a wet-SEM image of the sciatic nerve of a rat.)
The pictures produced by the new technique have a slightly lower resolution than do those produced by traditional SEM but provide higher magnification than optical methods do. In addition, the team notes, "An ability to observe fully hydrated samples at room or body temperatures could help eliminate many artifacts of sample preparation and allow routine and reproducible imaging."