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Detailed Explanation of SPM

 
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What are the techniques of microscopy?

Microscopy is a technique used to view objects invisible to the naked eye, or too small to be seen clearly. The size of the object being viewed can vary from nanometres - bacteria, single celled organisms, to millimetres -  small insects, & plant cuttings for example. There are 3 main microscopic techniques that are used: Optical microscopy, Scanning probe microscopy and Electron microscopy.

Optical microscopy

Also known as light microscopy, involves using glass or plastic lenses arranged in a tube, much like a telescope, to produce an enlarged image of any small object placed in the focal plane of the lens. There are many applications to Optical microscopy, but one of the main uses of an optical microscope is in medical diagnostics of tissues or free cells in a smear test. An optical microscope has limitations regarding the amount of useful magnification which can be obtained. This is due to a property of light itself, and the wave length of the light used to resolve detail in the subject. A light microscope (optical microscope), has a magnification limit of approximately 1600x. Optical Microscopy is also an affordable hobby for non-professionals where tiny organisms can be viewed readily with a microscope costing less than a $100.00 or £80.00.

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      Optical Microscopy Links

  1. Optical Microscopy Official Web Site

  2. Microscopy Monthly Magazine

  3. Microscopy Associations and Clubs

  4. Buying A Microscope (Web Site)

  5. Buying A Microscope (Book)

  6. Buying A New Microscope in the UK (Shop)

  7. Buying A Used Microscope in the UK (Shop)

  8. Optical Microscopy Library

  9. Microscopy Related Search Engine Microscopy

  10. Wikipedia

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Scanning probe microscopy

This is a highly specialised branch of microscopy where a probe  scans an object. A type of scanning probe microscopy is called STM (scanning tunneling microscopy) where a very sharp conducting tip is brought to the surface of an object and a voltage is applied between them.  The tunnel current is obtained and then used to trace the elevation of the surface of the object and thus produce an x-ray image. There are advantages and disadvantages to SPM, for example the major advantage is no need to use a vacuum. Disadvantages being that the maximum image is generally small and the detailed shape can be hard to distinguish of the scanning tip. This type of microscopy is outside the scope, range, and budget of non-professionals.

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Scanning probe microscopy Links

  1. Detailed Explanation of SPM


  2. Scanning Probes (types)


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Electron Microscopy / Electron Scanning Microscopy

This is a form of microscopy which uses an electron beam to scan an object instead of using light waves. The beam excites various surface structures of the probed object, which then emit secondary electrons that are detected and used to create an image on a monitor. An electron microscope has  a much higher magnification than a light microscope, so a much higher resolution and magnification is obtained. Resolution can be increased because as the electrons travel faster their wavelength becomes shorter so there is a direct correlation between reducing wavelength and increasing resolution.

There are two types of electron microscopes used: Transmission (TEM) and Scanning electron microscopes (SEM). A TEM is a microscope which fires a high voltage beam through a thin layer of a specimen to gather details of the structure. A SEM creates  images by detecting secondary electrons that have been emitted off the surface of the target object due to excitation by a primary electron beam. Although  highly detailed images are obtained using TEM and SEM microscopes, there are disadvantages as well. Unfortunately TEMs and SEMs are very expensive to build and maintain. They are very sensitive to magnetic fields and require cool water running through the lens constantly.  Using either a TEM or a SEM requires a high degree of specialised training and lies outside the scope of non-professionals.

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Scanning Electron microscopy Links

  1. Practical Uses of Scanning Electron Microscopes

  2. An Introduction to Scanning Electron Microscopes

  3. Wikipedia
     

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Quick Questions and Answers

Can I see viruses with a light (optical) microscope?
No. they are 1000x smaller than a bacteria, which is the smallest thing you can see with an optical microscope.

What is Microscopy in Biology?
In biology, microscopy, and studying biological forms with an optical microscope, is the most important way to gain insight into biological structures and processes. The majority of living organisms are far too small to be seen with the human eye, and cells and their organelles can only be seen with the aid of a microscope.

What is Staining in Microscopy?
Cell staining is a method used to better to reveal details of cells and cell components under a microscope. Using different stains, one can stain certain cell components, such as a nucleus or a cell wall, or the entire cell with different colours. These details are often transparent or semi transparent, but staining makes them more visible and different colours (organic dyes) enable various processes in the cell to be differentiated.

Stains, such as weak water soluble safranin, and crystal violet are often added to a sample. The Gram negative cells are stained red. The Gram positive cells are stained blue.

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What are the parts of an optical microscope?
Almost all optical microscopes consist of a tube, an eyepiece lens, a turret containing one or more objective lens, a light source, an aperture, a condensor, a stage, fine and coarse focus controls, and a sturdy base.

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How Do I Make My Own Stains?
Stains can be made using common household substances, mostly food colouring which are organic dyes. Common household dyes include red or blue food coloring, iodine or India ink. You can also obtain methylene blue or malachite green dye from the aquarium section of a pet supply store.


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How Do I Use A Microscope?
Place the slide containing the subject under the stage clips on the stage. Turn the revolving turret so that the lowest power objective lens is just over and close to the centre of the slide. Practice turning the coarse focus control so the stage moves away from the objective lens. Look through the eyepiece lens and watch for the subject to come into roug focus. Use the fine focus control to make the object appear in sharp focus.

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How much is a cheap usable microscope?
A low power simple microscope can cost around £60.00. These are best used by children, beginners, and first use of a microscope. Magnification will be from 10x to 40x. At approximately £80.00 the microscope will enable magnification up to 120x.
these microscopes are proper quality instruments with optical glass lenses. Do not buy microscopes from Toy shops which willprove disappointing.

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