Essential Materials
Creating a wet mount slide requires a few specific materials to ensure clear observation under a microscope. Standard glass microscope slides, typically 1 inch by 3 inches, serve as the base for your specimen. These provide a stable, flat surface on which to prepare your sample. Thin, square pieces of glass or plastic called coverslips are also necessary, commonly measuring around 22×22 millimeters, and they protect the specimen while flattening it for better viewing.
To suspend your specimen, you will need a liquid medium, often distilled water for general observations or physiological saline solution when working with living cells to maintain their integrity. A pipette or dropper is indispensable for precisely adding a small, controlled amount of this liquid to the slide. Finally, the specimen itself is the most important component, whether it is a drop of pond water, a tiny piece of plant tissue, or a cheek cell.
Step-by-Step Preparation
Preparing a wet mount slide begins with placing your chosen specimen in the center of a clean microscope slide. For liquid samples, a single small drop is usually sufficient, while solid specimens should be thin enough to allow light to pass through. If your specimen is solid, you might need to add a tiny drop of distilled water or saline directly onto it at this stage.
Next, carefully add a small drop of your chosen liquid medium, typically around 10 to 20 microliters, onto the specimen. The amount of liquid is crucial; too much can cause the coverslip to float, while too little can lead to the specimen drying out prematurely.
After adding the liquid, gently lower a coverslip over the specimen and liquid. This step requires precision to avoid trapping air bubbles. Hold the coverslip at a 45-degree angle, touching one edge to the slide just beside the liquid drop. Slowly lower the coverslip down, using a needle or toothpick to support it, until it completely covers the liquid and specimen. This angled approach helps prevent air bubbles.
Once the coverslip is in place, the liquid should spread evenly to its edges without overflowing. If there is excess liquid, you can carefully blot it away with the edge of a paper towel placed against the coverslip’s edge. This wicking action removes the extra liquid while drawing the coverslip down more firmly onto the slide.
Common Challenges and Tips
One frequent issue encountered when preparing wet mounts is the presence of air bubbles, which appear as distinct dark circles under the microscope and can obscure the specimen. If bubbles appear, gently tapping the coverslip with a pencil eraser or adding another tiny drop of liquid to one edge can sometimes help displace them. Another common problem is using too much liquid, causing the coverslip to float.
Conversely, using too little liquid can lead to the specimen drying out quickly, especially when observing living organisms. If the liquid starts to evaporate, you can add a small drop of water or saline to one edge of the coverslip, allowing it to be drawn underneath by capillary action. Sometimes, the specimen might be too thick or too opaque, making it difficult to view details under higher magnifications. In such cases, trying a thinner piece of the specimen or a different part of the sample can improve visibility.
Proper illumination and focus are also important for clear viewing. If the image appears too dark or too bright, adjust the diaphragm or condenser on your microscope to control the amount of light passing through the specimen. Fine-tuning the focus knob slowly will bring your specimen into sharp relief. Practicing the coverslip lowering technique is the most effective way to minimize air bubbles.