In many experiments, we have to view various samples to observe them properly. Sometimes, we may even need to use a microscope for tiny ones, but for a specimen like that, they have to undergo preparation and be placed in slides for viewing.
Slides are mostly composed of glass or plastic. On average, they measure about 1×3 inches and 1mm to 1.2 mm thick. They have different styles, and samples have to undergo various preparations before subjecting to a microscope. Here are some guides to help you.
The corners of a flat slide are all in 90-degree angles. Some have safety corners that are rounded to avoid cuts if mishandled. It is made of special glass and is flat and rectangular. It comes with a borosilicate cover glass or if you want, a plastic one, which has ground edges. They are perfect for blood samples because some have beveled edges with clipped corners.
For labeling, flat slides have frosted edges, which allow easy identification of samples. You will avoid contamination because the etched frosting keeps pen marks away from the specimen. You may even choose from various frosted colors. It may be useful for making categories if you would like.
Concave microscope slides are more expensive and may be used without a cover. They have one or more depressions on the surface, so they can hold liquid solutions and larger specimens. Plastic chambers with a fixed number of slides and covers are also produced by some.
On the other hand, you can observe samples placed in some flasks without clipping individual slides to the microscope. That is useful, particularly for those who are studying sediments. For observing cultured samples, there are also tray designs, so you can place the specimen in a refrigerator or incubator.
To save time and money, some people like researchers of histology or pathology, prefer electrostatically charged slides. That is because some samples, like cells and tissues, can’t stick to a glass surface. They need the surface to be modified or be positively charged.
Some slides are also water-proof or chemical-resistant if they are treated with biological reagents. That will protect the sample from contaminants in the environment.
There are also slides that have a graticule or etched grid system, which will help the scientist or researcher to focus on areas of interest. It will also serve as a guide for hand sketching, geographical plotting, and size and scale estimation. Some slides have dual concavity to allow side-by-side comparison while reducing the risk of cross-contamination. Others are made of transparent mica as a substitute for glass; it is less prone to dust and scratching and prevents glare.
To prevent the microscope’s objective lens from getting into contact with the specimen, a coverslip may be used. That is essential, especially in preventing leakage from water-based processes. It also protects the sample from unintentional movement, contamination, and holds it in place. Mostly, it is made of borosilicate or silicate glass. The coverslip is square, most of the time, and is thin, transparent, and has two types. Number 1 is 0.13mm to 0.17mm thick and is mostly used for oil-immersion processes and high-resolution microscopy. Number 2 is 0.17mm to 0.25mm thick and is used for other general purposes.
Some coverslips are rectangular, made from other materials (eg. quartz, certain plastics), have grids, or have different thicknesses.
Most of the time, they can be reused. You can remove and sterilize the coverslips. If you are making a permanent slide, you can glue it or use a sealant.
Preparation Processes and Techniques
Before being available for viewing, samples must first undergo some methods and be placed in slides. Varying samples will require different techniques, so here are some of the processes they require.
Thinly slice a part of the sample, place it in the center of the slide, and put a coverslip over it. That is the most basic technique you can use for observing particles, feathers, hair, and dead matter. You can also apply it in viewing insect or aphid legs or antennas. In theory, dry mounts can last indefinitely. Remember, you have to thinly slice the sample, especially for opaque ones, to let light pass through.
A wet mount is used for living or aquatic samples and natural observations. The specimens have to be suspended in oil, water, glycerine, or brine. In preparing, you will need to place a drop of the liquid in the center of the slide using a pipette. Then, you have to use tweezers to place the sample in the liquid. Next, lower the coverslip carefully and at an angle, to avoid bubbles. Lastly, you may use a paper towel to remove excess liquid. The wet mount method is applicable in a wide variety of samples.
As the specimens are living or need to stay in the water, wet mounts won’t last long. The liquid will evaporate and eventually, the samples will die. For example, a protozoan will only last for 30 minutes, but if you use petroleum jelly to seal the coverslip, it may extend its life for several days. Some samples may also move, so you can also add pieces of the ground coverslip, cotton, or chemicals to slow them down.
The method smear slide will require flat slides and will work best with liquid samples like blood. You only need a drop of the sample and smear it using the edge of a second slide. Make sure that it is evenly coated and carefully put a coverslip, do not trap bubbles, then remove excess. The sample will dry over time.
The samples in squash slides are mostly soft. It starts with a wet mount, and carefully pressing down on the sample. You have to be gentle to not destroy the sample or break the coverslip.
To reveal structural details, color contrast is needed. In staining, iodine, methylene blue, and crystal violet are used. You may add this to dry or wet mounts. Place a drop of the stain on one side of the coverslip, put a paper towel on the other side, and allow the dye to be pulled to the specimen.
There are also prepared slides that you can purchase and study. They are useful for educational purposes and can be used as a control for making comparisons.
Ensure that you are always using the proper equipment in making slides and observing them. Just remember this guide and you are good to go!