- Katherine Harmon
16 April 2013
Imaging specimens with electron microscopy imposes
conditions that are typically deadly for living things, such as a high vacuum. But
the electrons used to create the images might actually have a protective
effect. Researchers have found that the beam of a scanning electron microscope
can turn a thin coating that occurs naturally on the larvae of some insects
into a sort of miniature spacesuit that can keep the animals alive in a vacuum
for up to an hour.
Takahiko Hariyama, a biologist at the Hamamatsu University
School of Medicine in Japan, and his collaborators describe the results in the Proceedings
of the National Academy of Sciences.
The discovery builds on previous findings that
some organisms, including beetle larvae and ticks, can survive short stints in
the extremely low-pressure environment of scanning electron microscopes — and
even, in the case of dormant tardigrades, or 'water
bears', in outer space.
The researchers made their discovery while testing how long
various animals could survive in a high vacuum while being imaged inside a
scanning electron microscope. Most organisms to lose water rapidly in these
conditions, leading to death by dehydration and physical distortion, but the
larvae of the fruitfly Drosophila survived for 60 minutes and
went on to develop normally after being returned to normal pressure.
The cuticles of fruitfly larvae are naturally coated in a
substance made of biological molecules such as proteins, and the researchers
suspected that exposure to the electron beam caused molecules in the substance
to lock together in long chains, or polymers. That would create a flexible,
protective layer just 50–100 nanometres thick. Other organisms that have
similar coatings, such as Japanese honeybees (Apis cerana japonica) and
larvae of blue-bottle flies (Protophormia terraenovae), survived in the
high vacuum after being irradiated with plasma beams, which can generate a
polymerization effect similar to that of an electron beam. Plasma beams are
already used for that purpose in some industrial applications3.
To further test their hypothesis, the team tried applying an
artificial version of the coating — a detergent solution made from a surfactant
— on organisms that did not have one, including a flatworm (Dugesia japonica)
and the larvae of the Asian tiger mosquito (Aedes albopictus). Under
plasma irradiation, the coating formed a similarly effective nano-suit.
Structure saviour
The researchers also found that many structural details of
the surviving larvae were “completely different from that of untreated
specimens and traditionally prepared specimens”, suggesting that the nano-suit
was preserving the 'real-life appearance' of the specimens.
However, materials scientist Robert Sinclair of Stanford
University in California notes that the process might introduce additional
changes — and that the magnifications used in the study are relatively low for
electron microscopes.
If it proves sound, however, the technique "could
change the way in which some living organisms could be studied using
present-day electron microscopes", says Harry Horner, a developmental
biologist at Iowa State University in Ames. "Not only with organisms that
exist on Earth, but with organisms sent into space or retrieved from space
explorations."
Hariyama already has an eye on the skies: he and his team
hope to send small animals wearing nano-suits to space, and he says that they
have already had some success in nano-suiting small fish.
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