Optical Microscopy & Electron Microscopy

Posted: October 17th, 2013

Name:

Instructor:

Course:

Date:

Optical Microscopy & Electron Microscopy

Microscopy refers to the technical field of application of microscopes in the sampling of objects that cannot be perceived by the resolution range of the normal eyes. This field of study is divided into three: electron, optical and scanning probe microscopy. Microscopy has several techniques within each category for instance optical microscopy has the bright field, oblique illumination and dispersion staining as some of the microscopy techniques. Other less popular forms of microscopy include ultraviolet, infrared, laser and amateur microscopy.

History

The first designs of microscopes in the 17^th century were optical microscopes. The first attempts at making an invention closest to the microscope were in 1590 when spectacle makers Hans and Zacharias Janssen came up with a simple microscope. Much later in 1609, Galileo Galilee modified this model to include two concave and convex lenses. Anton van Leeuwenhoek popularized the microscope in the 17^th century by making extensive use of his homemade microscopes in his experiments. Major developments in the microscope include the 1893 Köhler illumination modification by August Köhler that improved the sample illumination. Modern microscopes have adopted the technology of fluorescence microscopy that displays specific structures in a sample (Neumeyer, 1999).

The advent of the electron microscope followed soon in 1931 when German engineers Ernst Ruska and Max Knoll designed a prototype of the electron that was able to magnify a cell up to four hundred times. Later in 1993, Ruska modified the microscope that increased the resolution that could be possible achieved by an optical microscope. Over the years, many modifications have been made on the original prototype made by Ruska and Max Knoll including a capability of magnifying of up to two million times (Gösta, 2012).

Structure and design

i) Optical microscopes

Optical microscopes are also commonly referred to as light microscopes. Their basic operation relies on visible light that is manipulated by a series of different lenses in order to magnify small objects. The optical microscope has a one simple lens and many compound lenses. The ingle lens collects light from the sample being viewed. In turn, the compound lenses focus it on the eye according to the resolution set by the user. Due to their simplicity of technology, optical microscopes are the easiest to use. The advantages of these types of microscopes are as follows. Optical microscopes have multiple lenses means that the microscope has an improved numerical aperture that only blurs images at very high resolutions.

Optical microscopes also have a lower chromatic aberration that refers to the distortion of colors as they pass through a lens. Lastly, the objective lenses can be exchanged to achieve a greater magnification. Although the present day optical microscopes function with great efficiency, there are still minor issues surrounding their use. Problems associated with light such as aberration, poor lens architecture and blurry images still haunt the optical microscope’s functionality. However, developments in the lens design by Carl Zeiss and other engineers have produced microscopes with sharper and clearer images (Mooney, 1996).

ii) Electron microscope

This is an advance microscope that uses electron beams to illuminate the sample and magnify it. There are two types of electron microscopes: transmission electron microscope (TEM) and scanning electron microscope. The TEM was the first original electron microscope that used high voltage electron focused in a beam to create an image. This made possible by an electron gun that emits these beams through a tungsten cathode that acts as the source. The electron beam passes through an acceleration process using an anode that is set at 100keV. The electron beam is then focused using electromagnetic lenses and electrostatic to the specimen.

The specimen reflects the beam that is now loaded with information about the scanned cell or sample in a magnified form by the objective lens of the electron microscope. The variation in the size of the magnification can be later changed by projecting the final image onto a photographic surface. The most preferred materials used commercially are phosphoric paper and zinc sulfide paper. Some types of microscopes record the image directly onto the photographic paper that is placed directly on the electron beam (Krumeick, 2012).

Electron microscopes use electromagnetic lenses to direct the path of the electron beam and use it to form an image. The types of lenses in electron microscopes are different from the typical optical ones. These lenses do not form an image by focusing light on to the specimen. The reason for this change in lenses was that electrons have shorter wavelengths than visible light. Theoretically, electrons have about 100,000 times shorter wavelengths. Therefore, electrons can achieve better resolutions that are difficult to achieve in optical microscopes owing to the diffraction problems.

Uses

The most common function of both electron and optical microscopes is tissue analysis. Medical practitioners, scientists and histologist use microscopes to analyze the structure of tissues, cells of small organisms. In this way, lab scientists can understand the different microscopic organisms that cause ailments in human beings for example bacteria, fungi and viruses that are very tiny but deadly. Other more powerful microscopes such as the atomic force models are used in studying the surface of individual atoms within a cell. In this way, many diseases have been discovered and treated thus saving lives.

In the crime prevention field, microscopes are also applied in the investigation of perpetrators. Police officers collect various kinds of material from murder scenes and accident scenes that are analyzed under microscopes to identify possible victims or perpetrators. The DNA results are then matched with the public database to identify the potential individual. Microscopes are also used in schools and educational institutional where science students can learn more by viewing cells under microscopes. At the higher levels, students also use them in botany, genetics and geology (Kenneth, Keller & Davidson, 2012).

Similarity and differences

Similarity

Both the optical and electron microscopes are used in the inspection of small organisms. The basic functioning of the two types of microscopes is similar. They both use a series of lenses that are designed differently and placed strategically to magnify tiny objects. These two microscopes also use stains in the preparation of their specimens for further viewing. Both the electron and the optical microscopes use light waves that is photons and electrons, to relay the images for the observer to view the enlarged object.

Differences

Electron microscopes are more efficient than their optical counterparts are. Electron microscopes ca show up to 100,000 times more magnification as compared to a measly 200,000 times maximum presented by optical microscopes. This is because using electron technology, electron microscopes evade various issues that are evident in optical microscopes. Optical microphones apply photons that have a longer wavelength than electrons. As a result, electron microscopes can achieve far better resolutions making them a preferred choice.

Related to the first point, optical microscopes are affected by the different features that light which cannot be controlled. While electron microscopes work under highly controlled environments that ensure the stability, optical microscopes are affected by reflection, diffraction and aberration. This produces slightly fuzzy and blurry images when using optical microscopes. However, even though the images produced by electron microscopes are clear and detailed, they are only produced in grayscale that is still not good enough. Electron microscopes are more expensive because they consume power.

Electron microscopes also use special electrostatic lenses that can maneuver the electron beams needed to form the images in the microscope eyepiece or the photographic film. On the other hand, optical microscopes use normal glass lenses that direct light onto a specimen that can then make an image visible to the human eye. In terms of cost, the optical microscopes are cheaper to acquire and maintain as compared to electron microscopes that are more expensive. They also require constant stable sources of electricity to operate.

Another major difference that maintained the usage of the optical microscope is that it can view living things. The light used in optical microscopes has no effect on living specimens. However, viewing live specimens under electron microscopes is not possible. This is because the electron beams from the microscope will kill them instantly. The beams do so by staining the live specimen with metals that can be scanned for reproducing an image. Therefore, when live studies have to be made, the optical microscope is preferred.

Work Cited

F. Krumeick. Electron Microscopy. The Electron Microscopy Site. Web.14 May 2012. Web accessed on 13 June 2012.

Gösta E. Nobelprize.org. Autobiography- Ernst Ruska. Web. 14 Jun 2012. Web accessed on 13 June, 2012

Kenneth, Spring; Keller, H. Ernst; Davidson, Michael W. Microscopy resources Center .Microscope objectives. Web. 2012. Web accessed on 13 June, 2012

Mooney E. Laboratory for Scientific Visual Analysis .The Optical Microscope. Web. 28 April 1996. Web accessed on 13 June, 2012

Neumeyer R. Microscopy –UK. Introduction to the Optical microscope. Web. April 1999. Web accessed on 13 June 2012.