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Simple and compound microscopes are a useful tool to magnify specimens and see the structure or characteristics of organic or inorganic objects. This is done using a microscope slide, which is a glass or plastic strip that the specimen is mounted on for viewing.
There are many ways to prepare a microscope slide, depending on the type of specimen and microscope. This covers the steps to prepare wet, dry, and smear mounts, as well as how to stain samples to prepare them for a microscope.
Whether for hobbies or educational purposes, suppliers sell prepared microscope slides that have perfectly mounted specimens. These require no preparation or adjustment at all. You simply look at them using a microscope.
Numerous types of prepared slides are available in different scientific fields, including single-cell organisms, animals, plants, epithelial cells, tissues, blood, organ samples, bacteria, algae, and coral. You can also obtain samples from different animal species, plants, or diseased human tissue.
Though it’s important to learn how to prepare a microscope slide properly, there are many benefits to using prepared slides. Some of the specimens available, such as diseased tissue or animal specimens, may not be easy to obtain otherwise. Prepared slides with verified specimens also act as controls and exemplars for students and researchers to compare.
Finally, prepared slides often come in sets and are usually permanent, so they can be reused again and again.
Wet mount slides are often used for living samples and transparent liquids. They’re prepared in several layers with the slide as the base, the sample, and a coverslip, or clear glass or plastic covering that’s placed over the liquid to protect the microscope and minimize evaporation.
Here are the steps to prepare a wet mount:
Put a drop of water, glycerin, immersion oil, or the liquid sample on the middle of the slide using a pipette. The liquid you use will depend on the type of specimen.
If the sample isn’t already liquid, use tweezers to position it in the center of the liquid drop.
The coverslip should be positioned at an angle to preserve the specimen. Start by placing the edge of the coverslip on the outer edge of the liquid drop, then slowly lower it to minimize air bubbles. If the liquid drop is too big, the coverslip won’t lay securely, and it may compromise the integrity of the image.
Dry mount slides may be a sample on a slide on its own or a sample covered with a coverslip, depending on the type. For standard microscopes, the size of the specimen isn’t critical. For compound microscopes, however, the sample needs to be prepared thin, even, and flat—ideally, one cell thickness.
Put the slide on a flat surface. Using tweezers, put the sample on the slide.
If the slide requires a coverslip, position it after the specimen is in the ideal position. Some specimens won’t need a coverslip, as long as the microscope isn’t likely to bump them. Soft samples can have a gently placed squash coverslip that leaves some space.
Smear slides are used when the liquid is too dark in color or too thick to view with a wet mount. Some examples of these liquids include blood and semen. Because the preparation affects the microscopy results, smears are more complex and precise to prepare.
Put a small drop of liquid onto the slide using a pipette.
Using a second clean slide, hold it at an angle to the first slide. Use the edge to touch the liquid drop. The liquid will be drawn to the edge where the slides touch by capillary action. Then, you can evenly draw the second slide across the surface of the first slide to create a smear.
Some smears will need time to dry for staining. If that’s not the case, place a coverslip onto the smear.
Some specimens require staining for visibility under microscopy. There are many ways to stain slides, including iodine, crystal violet, and methylene blue, which may be used on wet or dry mounts.
Prepare the specimen according to the wet or dry mount technique.
Place a drop of stain on the edge of the coverslip using a pipette. Position the edge of a tissue or paper towel on the opposite end. Capillary action will draw the dye across the specimen.
Preparing microscope slides is an important skill for hobbyists, students, and researchers to learn. With some specimens, an ill-prepared sample can have an effect on the precision and accuracy of the results. Learning the basics of preparing wet, dry, and smear mounts and staining also provides the foundation to work with more complicated specimens for complex microscopy.
Featured Image Credit: TippaPatt, Shutterstock
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Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.
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