Proper Slide Preparation for Accurate Observation
Using microscopes to observe a specimen is commonly practiced in almost all laboratories and research institutions worldwide. But small organisms just like a cell and a plant tissue cannot be viewed by itself alone. Samples that are not visible to the naked eye have to be properly prepared and mounted on the microscope in order to view it correctly.
To observe live microorganisms or other minute objects, they have to be properly placed on slides. Slides serve as the flat transparent glass container of the specimen being observed. It is then placed under the microscope’s objectives so that it can be magnified and viewed through the eyepiece. But viewing a specimen on a glass slide is not a simple as merely placing the sample then there and just putting it under the microscope’s lens. More often than not, some special preparations are required.
To prepare a slide for use with a microscope, a cover slip and a dye may both be necessary. A cover slip is a thin, usually square chip made of transparent glass or plastic that is placed over the specimen. This device ensures that the specimen is in place and intact. A dye, on the other hand, is a coloring agent. Most microorganisms are transparent or colorless in nature. It is therefore impossible to see a thing in that shade through the microscope’s lighting system. To make transparent samples viewable under a microscopes, they are colored using a special dye. A dye is a chemical compound known not to alter the structure of the specimen under observation other than change its natural hue.
There are two ways to prepare and mount a slide. The first one is a dry mount. As the name suggests, the sample here is dry. And the whole preparation procedure doesn’t require water at all. Dry mount is normally used for inanimate specimens that don’t need water in order to live.
To dry mount a specimen, get a glass slide and have it laid on a very flat surface. Put the specimen to be observed on the top of the glass. If you are to view a fingernail, for example, make sure it is thin enough. Then carefully place the cover slip on top of the sample. The specimen can now be viewed through the microscope.
The other method of slide preparation is wet mounting. Wet mounting requires water. It is a slide preparation technique that is commonly used to contain living organisms, whether or not they are mobile. Preparing the slide on a wet mount basically follows the same procedure as the dry mount technique. The only difference is that water is being added to the equation.
To do a wet mounting of a specimen over a slide, lay it on a very flat surface. Place a single drop of water on it. Then place the specimen on the water. It is also possible to put the specimen on the slide first then place a drop of water to it right after.
Putting the cover slip over the slide is the tricky part. To do it, hold the cover slip on its both sides. Make sure you hold it at 45-degree angle and then slowly lower it down. Doing this ensures that the water is spread out over the slide. Take out air bubbles by gently pressing them towards the outer edges.
Also make sure that all of the cover slip is covered with water. You can add a drop of water on each of the side of the cover slips and let it seep though. Conveniently use a paper towel to remove excess water.
There are also times that small microorganisms need to be slowed down so they can be viewed properly under a microscope. Chemical solutions like Prostolo can also be added to trap organisms. Prostolo can be mixed with water through the use of a cotton ball.
As stated earlier, some organisms are colorless. For these cases, staining them with either of these popular dyes, such as Lugol’s iodine, crystal violet, or methylene blue, is required. These solutions increase the organism’s contrast when viewed through the microscope. The preferred stain can be added directly to the water or after. If you aren’t sure if the specimen is colorless, view it first through the microscope. If you can’t see anything, proceed to add the dye.
These are the proper way to prepare a slide for viewing. Without doing these steps, accurate observation of the specimen won’t be attained. Proper slide preparation is a basic technique that every aspiring scientist should master