A microscope allows you to view magnified images of minute specimens. To use the instrument, you need glass slides, cover slips, mounting media, slide stains, and more.
A slide is a flat, rectangular piece of glass used to mount and view a specimen using a microscope. You can prepare slides using various slide mounting techniques. The prepared microscope slides are loaded onto the instrument and observed by focusing the lens.
Types of Slides: Flat vs. Concave
The two main types of slides include:
Flat glass slides. These are standard slides made of glass. They are 25 by 75 millimeters in size and 1 to 1.2 millimeters thick.
Flat glass slides require a cover slip or cover glass, which is a thin, square piece of glass used to cover soft-tissue samples or liquid specimens. It helps keep the specimen in one place on the slide and protects the microscope lens. A cover slip is 22 by 22 millimeters in size and 0.15 millimeters thick.
A cover glass is required to view a drop of liquid under a microscope. Without it, the liquid’s surface tension creates a dome-shaped droplet. This drop can touch the microscope lens and affect the image focus. A cover slip helps protect the microscope lens from touching or interfering with the liquid substance. It also breaks the surface tension, flattens the liquid drop, and allows detailed observation with minimal focusing required.
Concave or well slides. These are microscope glass slides with a small depression or well in the center to hold the liquid for viewing. Concave slides are more expensive than flat glass slides and can be used without a cover glass.
4 Common Slide Mounting Techniques
Here’s how to make microscope slides:
1. Dry Mount
This technique involves placing the specimen directly on the slide. You may use a cover slip, but you can view a dry-mounted specimen without one. However, ensure that the sample does not touch the microscope lens.
Dry mounts are used to view dry samples like plant materials like pollen, feathers, and hair. You may need to prepare the sample before dry mounting. If you are using a low-power microscope to examine the specimen’s surface, the size of the specimen does not matter. However, if you are working with a compound microscope, the specimen must be cut as thin or flat as possible for viewing.
2. Wet Mount
You can use the wet mount technique to view living specimens, clear liquids, and aquatic samples. It is suitable for examining organisms found in water such as paramecium and body fluids such as saliva and urine.
A wet mount involves sandwiching the liquid sample between the glass slide and cover slip. The cover slip helps flatten the sample, prevent evaporation of the liquid, and keep the microscope lens clean.
Live specimens that are not already in a liquid must be suspended in a fluid mounting medium for viewing. The medium for wet mounting can be a drop of a solvent like water, glycerin, or immersion oil.
Here’s how to prepare wet mount slides:
- Place a drop of the mounting medium or liquid sample at the center of the slide.
- If the sample is not already in a liquid, use tweezers to position it in the mounting medium.
- Take a cover slip in hand. Place one side at an angle such that its edge touches the slide and the edge of the sample drop. Then, gradually lower the cover slip. This technique helps prevent air bubbles in the sample.
- Avoid large sample drops as they make cover slips float and make it difficult to find and view the specimen.
- If the liquid medium evaporates from the sides over time, the living specimens may die. Use a toothpick or some petroleum jelly to cover the edges of the cover slip. This seals the specimen, prevents evaporation, and avoids air bubbles under the cover slip.
3. Section Mount
The section mount technique requires an extremely thin slice or cross-section of a specimen. An instrument called a microtome helps thinly slice the specimen. The slice is carefully placed on a slide. You can then use the dry or wet mount technique to prepare the specimen. Section mounts are suitable for samples that can be sliced, including solid objects like fruit and vegetables.
Some fluids like blood or semen are too dark, thick, or unclear to view using the wet mount technique. You can observe them by smearing a thin layer of the sample on a microscope slide.
To make a smear, place a small sample drop onto a slide. Take another clean slide and hold it at an angle to the first slide. Touch the drop with the edge of the second slide. Due to capillary action, the liquid forms a line where the second slide’s edge meets the first slide. Without applying too much pressure, evenly drag the second slide across the first slide’s surface to form a smear.
Allow the smear to dry for slide staining, or place a cover glass on it. An even smear allows you to observe individual cells using a microscope. But making a completely even smear may require practice.
Slide Staining Process
Stains are pigments that help identify different cell type and parts such as the cell wall or nucleus when viewing a microscope slide. Stains enhance the contrast of the magnified image, allowing you to observe the sample in greater detail. This enables easy classification of cells based on their size and structure. Stains can also help identify living or dead cells.
Commonly used slide stains include iodine, eosin Y, crystal violet, and methylene blue. You can use them to stain smears, sections, and wet or dry mounts.
Slide staining involves these steps:
- Load the sample in the middle of the slide using the appropriate slide mounting technique.
- Add a drop of stain on the sample using a dropper or a pipette.
- Ensure that the sample is fully stained.
- Cover the stained sample with a cover slip.
- Remove the excess stain using tissue paper.
- The slide is ready for viewing under a microscope.
Make Microscopy Easy With Slide Preparation Kits
Making microscopy accessible to all, AmScope offers simple and easy-to-use microscope slide preparation kits for science students and professionals. Our kits include standard slides, stains, a microtome, cover slips, a pipette, tweezers, and other essentials. With our slide preparation kits, you can practice the four slide mounting techniques and explore the world that’s invisible to the naked eye.
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