Microscope slides are fundamental tools for examining microscopic specimens, providing a stable platform for samples invisible to the naked eye. The primary purpose of preparing a slide is to present the specimen in a way that allows light to pass through it, enabling clear magnification and detailed study. This preparation is used in research, education, and various scientific analyses.
Gathering Your Supplies
Before microscopic exploration, gathering supplies is a necessary first step. You will need clean microscope slides and coverslips. Slides are thin, rectangular glass pieces, while coverslips are smaller, thinner squares or circles of glass.
A dropper or pipette helps accurately transfer liquids, and fine-tipped tweezers can manipulate delicate specimens. Common specimens include pond water, often containing various microorganisms, or thin epidermal layers from plants like an onion. Human cheek cells, gently scraped from the mouth, also make an accessible starting point. Distilled water or a saline solution (0.9% sodium chloride) provides a suitable medium for most living specimens, preventing dehydration and maintaining cell integrity.
Mastering the Wet Mount Technique
The wet mount technique is a foundational method for preparing specimens for immediate microscopic observation. Place a small drop of liquid, such as distilled water or saline solution, in the center of a clean microscope slide. Next, introduce your specimen into this liquid drop. For instance, a tiny piece of onion skin can be unfolded within the water, or a small sample of pond water can be added directly.
With the specimen submerged, take a clean coverslip and hold it at a 45-degree angle, touching one edge to the slide beside the liquid drop. Slowly lower the coverslip over the drop, allowing the liquid to spread evenly beneath it without trapping air bubbles. This gradual lowering helps to expel air and create a thin, uniform layer for optimal viewing. If excess liquid emerges, blot it away with the edge of a paper towel.
Adding Color with Stains
Staining techniques enhance the visibility of transparent or low-contrast specimens, making specific cellular structures more distinct. Many biological samples, such as bacteria or certain cell components, are naturally colorless, making them difficult to discern. Stains selectively bind to different parts of a specimen, absorbing certain wavelengths of light and thereby increasing the contrast.
To apply a stain to an existing wet mount, use capillary action. Place a small drop of stain, such as methylene blue or iodine, at one edge of the coverslip. Then, place a small piece of absorbent paper, like a paper towel, at the opposite edge. The paper will draw water from beneath the coverslip, pulling the stain across the specimen to permeate the sample.
Methylene blue is often used to stain animal cells, highlighting nuclei and cytoplasm, while iodine is effective for plant cells, making starch granules more visible. Always handle stains with care, as some can temporarily discolor skin or clothing.
Making Slides Last: Permanent Mounting
For long-term preservation and repeated study, specimens can be prepared as permanent microscope mounts. This technique ensures the specimen remains intact and observable for extended periods, unlike temporary wet mounts which eventually dry out.
The process involves dehydrating the specimen, often through a series of alcohol solutions, to remove all water. Following dehydration, the specimen is cleared, often using a chemical like xylene, to prepare it for the mounting medium. It is then embedded in a resin-based mounting medium, which hardens over time, permanently affixing the specimen to the slide and sealing it under a coverslip. This method creates a durable, archival slide that can be examined years later without degradation.