Electron microscopes are used to investigate the ultrastructure of a wide range of biological and inorganic specimens includingmicroorganisms, cells, large molecules, biopsy samples, metals, and crystals. Electron microscopes make images by beaming electrons at the subject matter. 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.
The problem is that it has to be done in a vacuum chamber, which means any living thing critter isn’t going to stay that way. Samples for a scanning electron microscope have to be specially prepared — even the water in a small creature’s body will evaporate, causing it to collapse.
Image courtesy of Dartmouth College
However a team of Japanese researchers have developed a new approach. The team have coated specimens in a non-toxic detergent called Tween 20 which is comprised of a thin polymer membrane or ‘nano-suit’ which enhances survival across the continuum between air and high vacuum. When they put the coated organisms in the vacuum and hit them with an electron beam, the detergent formed a lattice layer that protected the bodies. The research was published in the Proceedings of the National Academy of Sciences.
Most multicellular organisms can survive under atmospheric pressure. The reduced pressure caused by a high vacuum usually leads to rapid dehydration and death. Lead author Takahiko Hariyama, of the Hamamatsu University School of Medicine, has shown that a simple surface modiﬁcation can render multicellular organisms strongly tolerant to high vacuum conditions.
Hariyama came up with the idea after making scanning electron images of fruit fly larvae. He noticed that the electron beam didn’t kill the larvae. Later, he found out that some invertebrates have a special kind of molecule in their cuticles (the hard covering on the outside) that when exposed to electrons or ionized gas forms a protective layer. Other insects have a similar molecule.
Hariyama’s team tested the Tween 20 on the animals that did not have that special molecule, and got the same result — the animals lived. Animals that collapsed under high vacuum continued to move following exposure of their natural extracellular surface layer (or that of an artiﬁcial coat-like polysorbitan monolaurate) to an electron beam or plasma ionization (i.e., conditions known to enhance polymer formation). Transmission electron microscopic observations revealed the existence of a thin polymerized extra layer on the surface of the animal. The layer acts as a ﬂexible “nano-suit” barrier to the passage of gases and liquids and thus protects the organism. Furthermore, the biocompatible molecule, the component of the nano-suit, was fabricated into a “biomimetic” free-standing membrane. This concept will allow biology-related ﬁelds especially to use these membranes for several applications.
Field-emission scanning electron microscopes (SEMs) are highvacuum instruments (10−5
to 10−7 Pa) that are used for observingﬁne surface structures. When the SEM is used for biological materials, the specimens need to be killed, preserved, and stabilized (1). These complex procedures preclude the observation of living organisms and often produce unwanted artifacts. Researchers have tried to modify the SEM design to require lower levels of vacuum to circumvent such problems (2–5). However, all these methods require reduced vacuums (<10−3 Pa) and result in markedly inferior resolution. Observation of living specimens with a high-resolution SEM would be a signiﬁcant breakthrough. To
understand how animals can survive in a high vacuum would facilitate SEM analysis and would be a major advance in an attempt to more fully understand the role of the surface layer in protecting the organism.
Not everyone is convinced, though, that this method offers special insight into living invertebrates. Shippensburg University entomologist Gregory Paulson told The Scientist that the coating itself might affect how small structures on the bugs’ bodies look.