The History, Development and Use of the Light and Electron Microscope.

The History, Development and Use of the Light and Electron Microscope

Fatimah Jilani

Over time, our knowledge regarding matters in biology has developed quite rapidly with the use of microscopy. The use of microscopy has allowed us to look further into the physical side of biology especially in terms of cell ultra structures. Without the use of microscopes, we would never have even discovered cells let alone being able to know the characteristics and effects of minute detail, which is visible only through the Light and Electron Microscope.

During the historic period known to be the Renaissance, there took place the inventions of gunpowder and the mariner's compass which then lead to the discovery of America. However, during that period came the equally significant invention recognized as the microscope. The microscope being an optical instrument that uses a lens or a combination of lens to produce a magnified visual image of small minute objects. The invention of the microscope gave light to details of worlds within worlds. Looking at the advances of the technology behind the microscope you begin to wonder about the beginning of microscopes and what triggered off this development.

The earliest simple microscope was purely a tube with a plate for the object being viewed at one end and at the other end, there would have been a lens, which would give a magnification, which would be about ten times the actual size. At the time the main object of view were fleas and the microscope was dubbed as being the “flea glass.” Later on there were to come greater developments of the microscope. In 1609, a man named Galileo, known as the father of modem physics and astronomy worked out the principles of the lens and improved the microscopic instrument with a focusing device attached.

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During that century, the 17th century the best lenses were being manufactured in Holland. And from there, a Dutch man called Anton Leeuwenhoek became the first person to be able to see and describe cells and microorganisms using his own two-lens microscope. Due to this he became acknowledged as the “father of microscopy.”

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After Leeuwenhoek came Robert Hooke who continued the development of the microscope. Hooke developed Anton’s design by adding a third lens behind the two original two. This made the usage of the microscope a lot more comfortable. In the previous version of the microscope as in Leeuwenhoek’s design caused two main problems; the normal two lens microscope required you to look into the tube from a fairly long distance which meant that it was difficult to keep the tube in position and the two-lens design produced very dim images because of low brightness and contrast. So, with Hooke’s design the third lens improved the contrast and brightness of images and allowed closer viewing through the microscope. The modern microscope is still based on Hooke’s design in which the three lenses are replaced by multi-lens and mirrors to improve the quality of the images.

Eventually the microscope had revolutionised people’s way of thinking and the design of the microscope reached a point of faultlessness. Viewers were able to see live specimen and make conclusions on the object’s structure and function. Below is how you prepare the specimen for an optical microscope and an electron microscope:

Fixation: - The material has to be preserved in a life-like condition with distortion at its minimum.
Dehydration: - Any traces of water are removed from the material that is now fixed.
Clearing: - Dehydrating alcohol is removed from the material to make it transparent.
Embedding: - The material is then supported so that it is firm enough for sectioning.
Sectioning: - Slices of material are prepared thin enough to allow light to pass through.
Staining: - The material has to be stained to improve contrast between different structures, as most biological material is transparent.
Mounting: - Finally, the material has to be embedded and protected for viewing over long periods.

Using this method, light microscopes can reveal the structures of living cells and tissues, as well as of non-living samples such as rocks and semiconductors.

There was one common fault found and that was to do with the magnification of the microscope however much it was easy to use. The light microscope was unable to distinguish fine detail when the magnification increased. And this term magnification meaning the number of times larger that the image seen is than the specimen being viewed. The maximum magnification obtainable from a light microscope is x1500. The blurry images that started to be seen at the maximum magnification of the light microscope were because of the limited resolution. Resolution is the “degree of detail that can be seen.” The resolution of a light microscope is 0.2µm. This means that any two objects closer together than that distance are not resolvable as distinct and separate.

This disadvantage of the light microscope triggered off the development of a microscope being able to distinguish detailed structures of cells. The invention of the electron microscope by Max Knoll and Ernst Ruska at the Berlin Technische Hochschule in 1931 finally overcame the barrier to higher resolution that had been imposed by the limitations of the light microscope. Here was a device that when pushed to the limit was able to allow us to see small objects as small as the diameter of an atom, which was deemed incredible due to the x10 000 plus magnification. Below are examples of what can be seen through the electron microscope.

Fracture Surface of Paper Clip 100x

Organically Deposited Iron Oxide 10,000x

The electron microscope works similarly to the optical microscope however the difference being that beams of electron are used as a radioactive source rather than beams of light. In this invention the electrons are speeded up in a vacuum until their wavelength is extremely short-only one hundred-thousandth that of light. Beams of these fast-moving electrons are focused on a cell sample and are absorbed or scattered by the cell's parts to form an image on an electron-sensitive photographic plate. However, with the use of electrons there came a major drawback in this advanced technology. Specimens have to be specially prepared for viewing which require a lot of effort but aside from that due to the use of the vacuum and the electrons living samples cannot be viewed.

There are two types of electron microscopes, transmission electron microscope (TEM) and scanning electron microscope (SEM). The TEM the electrons pass through the specimen and are focused onto a fluorescent screen or directly onto a photographic plate. This is because the human eye cannot see electrons.

Optical Plan of TEM

With a SEM, electrons are reflected from the surface and collected to form a television-like image on a screen. They give a three-dimensional image of the surface of an object. The difference between the two microscopes is that the SEM has a poorer resolution but provides a three dimensional image for view. Also in the TEM the electrons actually pass through the specimen whereas they are reflected off the surface of the specimen in an SEM. Due to these two different types of electron microscopes, in terms of cellular structure we are able to view images from a cross-section of a cell not only in two dimensions but three dimensions. Alongside that, we are able to see in detail very small structures of the cell like ribosomes that are unable to be seen through the light microscope so we get a greater insight.

The development of knowledge of cells has been rapidly increasing since the usage of the light and electron microscope. The advantages of the light microscope include that it is cheap and very simple to use. Alongside that, it is small and portable. It is unaffected by any sort of a magnetic field. The preparation of specimen for the light microscope is fairly simple and quick. Also, the material is distorted by preparation. The natural colour of the material can also be viewed through the microscope. However, with all these advantages to the light microscope there are disadvantages. These include that the magnification is very limited to only x1500 only. The depth of the field is restricted. The electron microscope has quite drastic disadvantages, which are that they are extremely expensive to purchase as well as to operate. It is very large and must be operated in large rooms. It is affected by the magnetic field. The preparation of material requires a lot of effort and takes a long period. However, with these downfalls there are great advantages. With an electron microscope, you can magnify an object more than x500 000. It also has a high resolution and the resolution being 1nm. It is possible to investigate a greater depth of field.

We are now able enough to have a fair understanding of how cells work in biology and all due to the revelation of the sophisticated technology behind the microscope.

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