Microscope slides are used to examine single-celled organisms, and to closely observe small plants and organisms. There are two types of prepared slides: dry mount and wet mount. Each type of preparation method is used to perform the analysis of the different types of cells. If you are wet mounting a particularly pale or translucent specimen, you may need to stain the specimen so that it becomes visible under the microscope.
Method 1 of 3: Prepare a dry mount
Step 1. Choose a clean slide
Hold the slide in front of a light source and look through it to make sure there are no smudges or dirt. Most microscope slides are flat at the top and bottom, and have a rectangular shape. They are transparent, which allows light from the microscope to pass through them and illuminate the transparent specimen sample. If the slide is dirty, or has stains, you will not be able to effectively examine the specimen.
If you discover that the microscope slide is contaminated in any way, even with your fingerprints, wash it quickly using liquid soap and water. Dry the slide using a clean cloth. Do not use tissues or absorbent paper to clean it, as these could leave traces of lint on the slide
Step 2. Inspect the specimen and determine if it needs to be sliced
The specimen sample must be translucent (or semitransparent), or become completely transparent, so that light can pass through it. If the light is not able to completely pass through the specimen and into the microscope eyepiece, then you will not be able to see the specimen through the microscope.
Some of the specimens (for example, a strand of hair or an insect's wing) are thin and translucent on their own, so you won't need to slice them with a razor blade
Step 3. Slice a thin piece of the specimen sample
Use a razor blade to cut the specimen material into a thin, translucent slice. Dry mounts are the simplest to prepare, since they do not require the use of any liquid that goes between the slide and the specimen. A dry mount is ideal for the analysis of those samples that are not at risk of drying out completely. Among the materials that are commonly used in dry assemblies, we have:
- cork or wood for rafts
- flower petals or leaves
- insect legs or wings
- hair, fur, or feathers
Step 4. Place the specimen sample on the slide
Use a pair of forceps to pick up the thin slice of the specimen sample. Lay it gently on one side of the slide. If you are using a concave slide (which has a sunken side), place the specimen in the center of the concave area.
- If you are concerned about the specimen shifting back and forth, or slipping off the flat side, then mount the specimen on a concave slide. For example, if you are preparing a curly flower petal, and it is moving to one side or the other, then use a concave slide.
- A flat slide will work well with all other types of specimens.
Step 5. Place a coverslip on top of the specimen sample
The coverslip will prevent the specimen sample from sliding off the slide. The coverslip will also protect the specimen sample, in the event that one of the microscope users accidentally lowers the lens, and ends up pressing down on the specimen.
- Coverslips are transparent pieces of glass, or more commonly, plastic, which are quite thin. Each coverslip is approximately 2 cm (3/4 inch) in dimension, both in width and length.
- The slide will be prepared and ready for inspection under the microscope.
Method 2 of 3: Prepare a Wet Mount
Step 1. Pour 1 drop of water onto the slide
Use an eyedropper to pour 1 drop of water, exactly onto the center of a flat or concave slide. The water droplet is the reason why it is called wet mount. The liquid will keep the specimen sample moist, and will prevent the wet and organic specimen samples from drying out completely and distorting their shape. The water will also preserve living specimens, such as single-celled organisms.
If you would like to make a permanent slide using dead organic material, you can use a thin layer of clear nail polish instead of a droplet of water
Step 2. Scrape or slice a section of the wet sample from the specimen
The specimen samples used to prepare wet mounts are generally live or wet organic material. Use a razor blade or toothpick to cut or scrape off a small amount of the wet specimen. Among the materials that are commonly used to make wet mounts on slides, we have:
- Cheek cells or dental plaque (a scraping is done inside your mouth using a toothpick).
- A thin cross section of a plant stem (cut with a razor blade).
- If you are going to study single-celled organisms (such as an amoeba or a paramecium), the use of tweezers will not be effective. Instead, use a clean eyedropper to collect a couple of drops of water, in which the single-celled organisms or algae are submerged.
Step 3. Place the specimen sample in the drop of water
Depending on the type of material you are using as the specimen sample, you will need to use a pair of forceps, tweezers, or a toothpick to transfer the specimen onto the slide. Place the specimen in the center of the water droplet so that it is suspended in the liquid.
If you are using an eyedropper to collect single-celled organisms, then pour 1-2 drops over the drop already on the slide
Step 4. Place a coverslip on top of the wet specimen
Hold the coverslip at a 45-degree angle. Place one of the edges exactly to the side of the specimen over the drop of water. Then lower the other side of the slide until it is completely horizontal on top of the specimen. You will see the water droplet (s) spread under the coverslip all the way to the edges.
Do not bump or apply pressure to the coverslip once it is in position. If you do, you run the risk of squeezing the specimen sample along with the water, causing it to come off the slide
Method 3 of 3: Stain Cell Specimens
Step 1. Place a sheet of absorbent paper over one edge of the coverslip
Lay the paper over the edge of the coverslip without disturbing the material underneath. The absorbing power of the absorbent paper will draw some of the water from the inside of the coverslip, and will draw the staining agent under the coverslip onto the specimen.
- If the specimen, on which you are wet mounting on the slide, is pale or colorless (for example, the cross section of the stem of a colorless plant), it may be difficult to observe through the microscope. Performing a staining of the specimen will allow you to observe its shape and texture, in a better way.
- This step is generally performed after the wet specimen has been examined on the slide, without staining it. The slide may already be ready, even if staining was not performed.
Step 2. Pour 1 drop of iodine or methylene blue onto the other side of the coverslip
Use an eyedropper and pour the staining chemical on top of the slide, directly to the side of the coverslip. Be careful and pour only 1 drop. It is possible that excess staining agent may slip off the slide.
- You can buy iodine or methylene blue at any educational supply store, or biology supplement store.
- An alternative way to do this is to pour the drop of staining agent into the water on the wet mount slide when you first prepare it. In this case, you won't need to use the absorbent paper.
Step 3. Wait until the staining agent is spread under the coverslip
The staining agent will begin to seep under the coverslip as the absorbent paper draws water from the other side. It may take up to 5 minutes for the iodine or methylene blue to sink below the coverslip, and soak into the specimen.
Once the iodine or methylene blue has spread over the entire area of the coverslip, then complete staining of the specimen has been performed
Step 4. Wipe off excess staining agent using a clean absorbent paper
Removes impurities from the surface of the slide so that no loose liquid spills down the side. The stain on the wet mount is ready for viewing under the microscope.
- Microscope slides and coverslips are small and delicate. Always handle these items with care, as they can easily shatter or scratch. Never drop a slide or coverslip, and also place them only on clean counters.
- Iodine and methylene blue are poisonous substances, so you should never ingest them. These substances will also stain the skin (temporarily), and clothing (permanently), so wear clothes that no longer serve you, when you go to handle these chemicals.