Some people may still feel unfamiliar when they hear the name electron microscope. This type of microscope is rarely used in schools and is only used for research purposes.
This microscope was invented by scientists from the university of Berlin, namely Dr. Ernst Ruska and Max Knoll in 1931. Because of the invention of this microscope, in 1986 Ruska was awarded the Nobel Prize in Physics.
Before the invention of the electron microscope, the world was familiar with the use of light microscopes. At that time, the light microscope was a very sophisticated tool.
However, with the invention of this type of microscope, the use of light microscopes has shifted. This is because the microscope that utilizes the energy of electrons is able to magnify up to two million times on the object.
Because of its sophistication, electron microscopes are often used in research or industry. For example, it is used to study the shapes of animal and plant cells, study the structure of viruses and bacteria, and study the surface of objects. In the food processing industry, this tool is used to classify types of flour.
The invention of the electron microscope The invention of the electron microscope began with the discovery of the phenomenon of electrons in 1920. Electrons would have a light-like character if their motion was accelerated in a vacuum and in an electromagnetic column.
With a wavelength 100,000 times smaller than light, electrons will use more energy than light. Therefore its use will be more efficient when compared to a light microscope.
In this phenomenon it was also found that there is an electric field and a magnetic field around the electrons. These two fields have the same role as the lens and mirror in a light microscope.
In other words, in the electron microscope the control of lighting and image appearance is carried out by electrostatic and electromagnetic fields. This is what makes it have a very high object magnification capability resulting in better resolution.
The design of the microscope was finally made after going through various types of research. The model used is the same as the microscope model in general, which is a development of the design of Galileo Galilei.
Galileo's model of the microscope is actually an imitation of the Kepler binoculars design. The difference with binoculars is that the resulting image is an enlarged inverted image.
Objects to be observed using this type of microscope must be placed in a vacuum. Therefore, this tool can initially only be used to observe inanimate objects.
In this vacuum, the object will be fired by a beam of electrons whose wavelength is only 1/100,000. With this small wavelength, the electron beam will not be visible to the eye because it is only white light.
The electron beam that is fired will be reflected back by the object being observed. The reflected light will be caught by an object such as a negative film which is sensitive to electrons. As a result, the object image will be printed like a photo on the film.
With its magnification capability, it will produce a film image with a fairly high resolution. Thus, the observation of the results of the image from the microscope will be more accurate.
Transmission electron microscope or commonly known as TEM is a microscope that works similarly to how a projector works. In this tool, electrons will be transmitted (transmitted) into the observed object.
Meanwhile, observers can see the results on a screen such as on a slide projector. Initially this microscope was made using only two magnetic fields as lenses. This tool was later refined by the addition of a third lens.
When demonstrated for the first time, this tool is capable of producing resolutions up to 100 nanometers. At that time, the value of this resolution was much better than the use of a light microscope.
The performance of this tool is also increasing until it can produce magnifications of up to one million times. The resolution obtained also reaches 0.1 nanometers or the equivalent of one angstrom. Therefore, its use in the field of science is growing rapidly.
However, many parties are not satisfied with the discovery of this transmission electron microscope. This is because the observed object must be as thin as possible. This factor is an obstacle for some researchers who have thick objects.
They cannot observe the object using this application of the electron phenomenon. Therefore, research to develop new methods on this type of microscope continues.
Before observing the object under a transmission microscope, it is necessary to carry out a preparatory stage for the object of observation. This is done so that the observer can observe the object properly.
The first step is to fix the object to kill the cell without changing its structure. The second step is to make the incision as thin as possible on the object so that it is easy to observe. The incision formed is then stained to distinguish it from the surrounding environment.
Scanning Electron Microscope
A scanning electron microscope (SEM) is a microscope that works using an electron scanning technique. Until now, it is not known who actually invented this tool.
There are two scientists from Germany who have claimed that this microscope is the result of his invention. First, namely Dr. Max Knoll who published it in 1935. Second, Dr. Manfred von Ardenne who claims to have researched the phenomenon of the electron in 1937.
Do not want to drag on in search of who first discovered it, the development of the electron microscope continues. Finally, in 1942, a new microscope design was made by three American scientists, namely Dr. Vladimir Kosma Zworykin, Dr. James Hillier, and Dr. Sneijder.
The design form is a development of the original design. The built microscope has a resolution of up to 50 nanometers with a magnification of 8,000 times.
SEM microscopes that exist in modern times today have a resolution of up to one nanometer with a magnification of 400,000 times. This scanning microscope works by focusing its electron beam on the surface of the object being observed.
The object image obtained is a signal of the reflected electron phenomenon detected on the object's surface. The image results are then displayed on a monitor screen made of cathode ray tubes.
This scanning microscope is widely used to observe the surface structure of cells and microorganisms such as bacteria and viruses. The initial stage to prepare the object of observation is the same as in TEM, namely fixation.
The difference is, the object being observed does not need to be made into a thin incision. Therefore, SEM can be used to observe objects in three dimensions. After that, the stages of dehydration (removing water molecules) and staining are carried out so that the object is ready to be observed.
Techniques for Preparation of Samples to be Observed on an Electron Microscope
Objects to be observed using a microscope must be prepared properly. That way the sample taken from the object can meet the observation requirements.
Some of the techniques used include fixation, dehydration, cutting, and staining. Not all of these techniques can be performed for observations using different types of electron microscopy.
The first technique used is fixation on the object of observation. This method is done to prepare the sample to look like the real situation. The trick is to add glutaraldehyde and osmium tetraoxide to the object to be observed.
In addition, cryofixation methods can be used, namely freezing techniques using liquid nitrogen or helium. By using this method, the water present in the sample will form crystals.
The next technique is to replace water molecules using organic solvents. Next, the object is divided to get a thin incision. Previously, resin was inserted into the object to separate the body parts.
Cutting is usually done with a diamond-edged knife to form a thin incision so that the sample becomes semi-transparent to electrons.
The last technique in sample preparation is the staining technique. Samples are usually stained using a heavy metal such as tungsten. In addition to tungsten, other chemical elements that can be used for coloring are uranium and tin.
Staining is done so that the electrons in the object can be decomposed so that their appearance contrasts with the surrounding structures. This technique is done because some biological objects have a body color that is almost transparent to electrons.
In recent years, microscopes based on the electron phenomenon have not only been used for laboratory research. Several companies began marketing this tool to the public.
The advertisements he makes also attract the attention of consumers because they show a picture of a living object as a result of observation. There are also some manufacturers who add video to this electron microscope so that the life journey of the object can be recorded.