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TheGreatestMinds

The Final Frontier

(Is Really, Really Tiny)

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     There are those who say that space is “The Final Frontier” – the one place about which mankind knows very little. Others point to the deep oceans, noting that “we know more about the dark side of the moon than we do about the deepest parts of the ocean on our own planet”. Both of these opinions are correct. Yet there is a third horizon that is just as mysterious and this one is right underneath our noses: the world of the very small. It is a world of curious structures, beautiful shapes, tiny bacteria and even smaller viruses. Despite its microscopic scale, it is a world of surprising sophistication and, often, great beauty. As research scientists, we have been lucky enough to explore this world for over a decade and now; in each case, making the entire exploratory journey from the comfort and convenience of a cool and quiet basement, peering down a microscope.

 

     The human eye can see objects that range from many metres or even kilometres, down to those that are just 0.02 millimetres across – about half the width of a human hair. Below that, a magnifying glass – or low–powered “dissection” microscope can be useful to see things that are smaller still – details like the hairs on an insect’s leg or the scales on a butterfly’s wing. A standard light microscope of the type found in high schools and medical laboratories across the world can magnify things further –to about 1,000 times. At this magnification, germs come sharply into focus, as do the organelles inside cells of the human body. There was a time when this discovery alone – the invention of the light microscope – changed the whole of human history. The microscope meant that people could see the tiny organisms that cause diseases for the first time –a bit like seeing a whole new category of “animals” that had previously escaped notice. Of course, scientifically, this was revolutionary, but it also caused a stir amongst the general public, or, at least, the educated public of the day. When Robert Hooke published a collection of his sketches made down a light microscope, the book– “Micrographia” –was an instant best seller; the pictures of the humble flea and the house fly that he drew remain iconic images in the history of science and even science–art.

 

 

     However, like every tool that has ever been invented, the light microscope has limits; anything smaller than about one two–thousandth of a millimetre was still invisible. In 1931, along came another tool –the electron microscope– and, with that, mankind could glimpse an even smaller world for the first time. In fact, an electron microscope can magnify things over a million times more than the naked eye. In our own field, of optical effects in living organisms, the most useful magnifications are in the range of 5,000 times to 40,000 times more than can be seen with the naked eye. This is at the lower to middle end of what an electron microscope can accomplish – other subject areas need far higher magnifications, but it is still significantly beyond anything attainable with a light microscope. For this reason, there was a flurry of scientific papers and discoveries in our field in the 1940s, from about 1942 onwards –a period that coincides exactly with the first applications of the electron microscope to the subject. In science in general, people tend to single out new theories and hypotheses as the moments when mankind’s scientific understanding leaps forwards, but, often, these breakthroughs can only occur after a less publicised improvement in the tools being used by scientists in the field. Better tools give better data and unveil anomalies that cause the greatest minds in any subject to rethink their view of the world. In our own field, the development of the electron microscope was key–nothing in the subject made a great deal of sense prior to its innovation, despite the almost heroic efforts of pioneers like C. W. Mason and, for that matter, Robert Hooke and Isaac Newton, who were working without the tools we now take for granted. You could say the same for many fields–the discovery of the structure of DNA– and hence the mechanism of its function– was only possible because of the invention of X–ray crystallography – Rosalind Franklin’s beautiful images of DNA’s double helix allowed James Watson and Francis Crick to visualise the molecule’s shape and those images were only attainable because of the invention of this technique. More recently, the development of a fluorescent marker (GFP) from a naturally occurring jellyfish paved the way for literally thousands of discoveries in molecular cell biology. Without the chemical “tool” of GFP, those discoveries could not have been made – that research would have proceeded slowly, if at all, until the innovation of a similar marker; the science would have had to “wait” for the development of the tool. So, the theme of developing newer tools to shift our scientific understanding is one that recurs, time and again.

 

 

     Today, 85 years after the first electron microscope was built, it is still used at the forefront of modern science. Yet for all its many advantages, this tool, too, has restrictions. Electron microscopes work poorly in areas with a lot of vibrations – even heavy traffic on nearby roads can disrupt an image if the microscope is not properly protected from those vibrations. Sample preparation is complicated, too;  for instance, in the most widespread types of electron microscope, any sample needs to have metal within it, so that the electrons can interact with /“bounce off” the metal they encounter. With no metal in the sample, they will simply accumulate in the sample’s tissues, in one type of electron microscope or pass right through them, in another and create no image at all. This may sound like a major problem – how do you examine a piece of skin, or a plant leaf, for example, when neither contains any metal? But the answer is to prepare samples by soaking them in a solution of metal salts, or coating them in metal before placing them in the electron beam. The tiny metal particles coat, or highlight, the structures that we wish to see. It is like looking at a plaster cast, to see shape of the object that used to be found in the middle. In the case of the scanning electron microscope, the metal used is a very fine layer of pure gold deposited around the outside of the sample, like the thinnest of shells. For the transmission electron microscope, the process is more complex and uses a variety of highly toxic heavy metals– salts of Osmium and Uranium and Lead, for example –in which the sample is successively soaked and "pickled".

 

 

     For many years, one of our tasks has been to squint down a scanning electron microscope at little parts of animals that are coated in pure gold. Sometimes this means things like bird feathers or the edge of a seashell. More often, though, it is insects or little parts of them – tiny scales from the wings of butterflies or even scales from the backs of beetles. From living tissue or plant growing in the wild, to item under the microscope, each sample may take many days to prepare, even if individual steps in the process can be completed much more rapidly. It is also extremely fiddly work. Yet, when we have the finished samples in front of us, looking at first 1,000, then 5,000, then 12,000 then 14,000 fold magnification, we are lucky enough to see things that no person in the whole of human history has ever seen before. We would like to say this is because we have exceptional ability, but the truth is more prosaic. There are so many creatures on the Earth that no one person could ever take an electron microscope to examine each and every single one. That would be the work of many lifetimes. So, as yet, there are a great many creatures that have not been examined like this at all. In short – there is a tiny world out there, just waiting to be discovered – the complex, beautiful and varied world right beneath our noses; one of the greatest joys of being a scientist is seeing for the very first time.

 

By V. L. Welch & Dr Sébastien Mouchet.

The wing "hairs" of  The Purple Emperor butterfly (Apatura iris), have an intricate mico-architecture, when seen with a scanning electron microscope. Butterflies in general are known for having frequently very complex mico-anatomy and nano-anatomy that only becomes visible with the aid of an electron microscope.

The compound eyes of insects are composed of regular hexagonal "omnitidia" (lenses); these can be very striking when seen with a scanning electron microscope

When seen with a scanning electron microscope, the scales of butterfly wings (pictured) have been likened to tiles on a roof.

Museum specimen unidentified species Pachyrrhynchus beetle croped shurnk to 800copyright V 2 Transmission Electron Microscopy reveals some of the minute architecture of this  Pachyrrhynchus gemmatus purpureus beelte cuticle in cross section Pachyrrhynchus  weevil SEM showing antenna and some scales shurnk to 800pix copyright VLW Apatura_iris with credits A.iris 31 copyright S Mouchet shrunk to 800pix

An antenna and scales of an Asian weevil, seen with a scanning electron microscope.

Transmission Electron Microscope images can be more difficult to interpret than those from a Scanning Electron Microscope. This is a cross section of the cuticle of a metallic purple beetle.

Brightly coloured rainforest weevils, such as this Philippine species often have intricate and beautiful details when seen through an electron microscope.

Scanning Electron Microscope image of the brightly coloured wing-scales of the Purple Emperor butterfly, Apatura iris . Produced in the course of research by

S. Mouchet.

The male purple Emperor butterfly, Apatura iris, is one of Europe's most arrestingly beautiful flying creatures. This image is from wikipedia by Kristian Peters. It has a creative commons attribution licence-see image for webaddress.