Basic Guide to Preparing Microscope Slides

Prepared slides The world is full of wonderful things that we are unable to see with our naked eyes. Isn’t it an exciting prospect to see how a single strand of your hair would look if magnified, or to see what your blood is made of? These are all possible with the use of a microscope – if you have the competence to prepare microscope slides properly. However, there’s nothing to worry about, it’s very simple. The first step is to be aware of the required materials to perform this activity. They are presented below for reference.

What Will You Need to Prepare the Slides?

1. Slides – Glass or Plastic? 

  • In general, there are two kinds of microscope slides – the glass slide, which is the common one, and the well slide or depression slide. Both are rectangular in shape and measure 1 by 3 inches or 25 by 75 mm. The difference is that the depression slide can be used without a cover slip. It has an indent or hollow portion in the middle, which is known to hold liquid for specimens that require it for better visibility.
  • A standard slide is either made of plastic or glass, but most microscope experiments use the latter with a thickness of 1 to 1.2 mm. However, a glass slide measuring 0.8 to 1 mm thick should be used for high-level purposes and condensers. These slides are normally available in the market in increments of 72.

2. A Cover Slip

  • Also known as a glass cover – this is a super thin piece of either glass or plastic that is used to cover specimens during an experiment.
  • A cover slip helps flatten the specimen and the water preventing unnecessary movement of the sample being viewed. This allows the user to have a better focus or view of the specimen.
  • This material is very delicate, hence it must be handled with care. The measurement is 18 mm or 20 mm square.
  • A cover glass is also available in Number 1 thickness and Number 2 thickness. Number 1 cover slips are 0.13 to 0.17 thick while number 2 slips are 0.17 to 0.25 mm thick. The 1 variety is recommended for high-resolution or oil immersion type of work. While, the 2 variety is generally used for general tests or applications.
  • This material is sold in the market by the ounce. Each ounce contains 120 cover slips.
  • If handled carefully, glass cover slips can be reused several times after proper cleaning.

3. Dropper

  • A dropper or a pipet is simply a medicine dropper. This material is very affordable and can be reused after proper sterilization.
  • Longer droppers are available for long bottles or containers.

4. Optional tools – These tools are not essential, however are incredibly useful when preparing and using microscope slides:

  • Tweezers – These will make it easy to handle the specimen, slides and glass cover slip. They will also help prevent contamination and control a heavy hand.
  • Tissue paper – It’s always handy to have absorbent tissue paper close by, this will enable you to quickly and easily clean up any spillages and absorb excess residues from your slides.

Methods of Preparing Microscope Slides

Microscope slides can be prepared with a dry mount, a wet mount, and a prepared mount. Each type of mount is used depending on the sample that will be examined and observed under the microscope. Each type will also require specific skills and knowledge before it can be performed as there are advantages and disadvantages to consider for each one.

1. Dry Mount – Perfect for Beginners

A microscope slide using a dry mount is the most simple and easiest slide to prepare. It only uses a glass slide and a glass cover slip. This mount is recommended for specimens such as hair, pollen, feathers, and even dust found in the surroundings e.g. simple specimens that are not osmotically sensitive.

How do you prepare a dry mount? 

Preparing a dry mount slide follows very easy steps. All the user has to do is put the sample on the glass slide and cover it with the cover slip. It’s really that simple.

Disadvantages – Although this type of mount is easy to prepare, it comes with some key drawbacks. For instance, this type of microscope slide mount is only temporary except if you can fasten or seal the cover slip permanently. Also, complex or more intricate samples using a dry mount will be difficult to view under the microscope. Adding a few drops of water or stains may be required, which is what is done for wet mount slides.

2. Wet Mount (or Temporary Mount) – The Most Commonly used Technique 

A microscope slide using a wet mount provides a number of advantages. Putting a few drops of water or chemical stain on a specimen makes it more visible under the microscope. For live specimens, the water will allow the user to view its movement or motility and observe cell division.

How do you prepare a wet mount? 

  • To prepare a wet mount microscope slide, simply place a few drops of the required liquid on the slide using the dropper before placing the specimen in the centre of the slide.
  • Next, add a few more drops of liquid until the specimen is covered. This will reduce the risk of air bubble formation when you position the cover slip.
  • Cover the specimen using the cover slip, do this slowly and gently, at a 45 degree angle – this will help prevent the formation of air bubbles.
  • Extra liquid may need to be removed as necessary, you can do this using some tissue paper, which absorb any excess liquid.

Types of wet mount – Water and glycerin are two of the main types of liquid that can be used to make a wet mount microscope slide. The type of liquid that should be used will depend on the specimen or sample to be tested. For example, glycerin has a high refractive index, so will enable observation of small cell structures. It also acts has a preservative, allowing the sample to last much longer than usual.

Disadvantages – While this type of microscope slide provides several benefits, there are still disadvantages to consider. Wet mounts have a tendency to dry faster when put under the microscope, since the heat from the microscope lamp will evaporate the water. If this happens, just add a few more drops of liquid to it. In addition, wet mounts can not be stored, hence why they are termed a temporary mount.

3. Prepared Mount – Typically used by Experienced Professionals 

  • This type of microscope slide is more difficult to prepare, hence it is mostly used for pathological or biological work. The advantage is that this mount can used for a longer period of time after being created.
  • To create this type of mount, you need a specimen that is sliced very thinly. For best results, a user may use a microtome, which is known to slice items into featherweight-like pieces. Once this is done, put the specimen on a wet slide. Excess liquid must be removed as necessary. Depending on the sample that you have, you can either air dry or use heat to dry it. After, methylene blue can be applied to stain the specimen then put the cover slip on top.