Are you ready to explore the building blocks of life and the secrets of everyday objects? Our guide will walk you through properly mounting, staining and preparing microscope slides.
The easiest way for beginners to get started with microscopy is to purchase pre-prepared slides, normally coming in a kit of 50 or 100 slides. If you are ready to make your own slides, this guide will walk you through each step of the process!
Now what is a microscope slide?
A microscope slide is a thin piece of glass that is used to hold specimens for observation at high magnification under a biological or compound microscope. They also make storing, preserving and transporting specimens incredibly easy!
Why is slide preparation important?
You might be wondering, “Why go through all this trouble to prepare a slide? Can’t I just put something under the microscope and look at it?” Sometimes, yes! But for most microscopic observations, proper slide preparation is essential. Here’s why:
- A well-prepared slide offers clearer observations, and some techniques allow specimens to be preserved for future research.
- Preparing a slide properly lets you see intricate structures that would otherwise be invisible.
- Imagine trying to understand the inside of an orange by just looking at the whole fruit. You wouldn’t see much! Techniques like sectioning reveal internal organization for deeper analysis.
- Many microscopic structures are nearly transparent. Staining adds color and contrast, making important features stand out!
There are two main types of microscope slides:
Flat Slides and Concave Slides
A flat slide is a standard microscope slide with a completely flat surface, which are better for solid specimens or thin liquid layers. They require a cover slip which is a small, thin piece of glass used to cover the specimen on the slide.
This differs from concave slides which have a depression or “well” in the centre, designed to hold liquid samples without needing a coverslip.
How to Prepare Microscope Slides?
Materials Needed
- Blank Flat Slides or Concave Slides
- Chosen Specimen
- Personal Protective Equipment (PPE) (e.g. safety glasses and gloves)
- Cover Slips (optional)
- Distilled Water
- Sterile Dropper/Pipette
- Sterile Tweezers/Forceps (for dry mount)
- Inoculation/Smear Loop (for smear mount)
To perform a Slide Staining, you will also need:
- Stain Solution
- Staining Rack
- Blotting Paper
Dry Mount
Dry mounting is the simplest method of preparing a microscope slide. It involves placing a dry specimen directly onto the slide and covering it with a coverslip, without using any liquid.
Dry mounting is best for specimens that are already dry and won’t be damaged by the lack of moisture.
Examples:
- Dust, pollen, and spores: These are inherently dry and often very small.
- Hair, fur, and feathers: These are relatively sturdy and don’t need added moisture.
- Insect wings, legs, or exoskeletons: Small, dry insect parts are ideal.
- Textile fibers (cotton, wool, etc.): These can be examined for their structure.
- Thin slices of dry materials (e.g., cork): If you can slice something very thinly and it’s dry, it can be dry mounted.
- Sand or soil particles: Good for observing mineral composition (though larger grains might be difficult to see clearly).
- Powders: Such as spices.
Steps:
- Place the specimen directly onto a clean and dry slide
- Place one edge of the coverslip against the slide, next to the specimen. Gently lower the coverslip over the specimen at a 45-degree angle, allowing the air to escape as it closes.
Wet Mount
Wet mounting is a fundamental technique for preparing microscope slides, used for viewing specimens that require hydration or are already in a liquid solution.
It involves placing a specimen in a drop of liquid (usually water) on a slide and then covering it with a coverslip.
Examples:
- Pond water: Allows you to observe living microorganisms like amoebas, paramecia, and algae.
- Plant cells (e.g., onion skin, leaf): Water helps maintain cell turgor and makes cell structures more visible.
- Yeast: Observe budding yeast cells in an active state.
- Protozoa cultures: Any prepared culture of microscopic organisms.
- Thin sections of fresh plant material: If you have a very thin slice of a fresh leaf or stem, a wet mount is necessary.
Steps:
- Place a small drop of water (or the appropriate liquid) in the centre of a clean microscope slide.
- Carefully place your specimen in the drop of liquid.
- For liquid specimens (like pond water): The specimen is already in the liquid.
- For solid specimens (like a thin leaf section): Use tweezers/forceps to gently position the specimen in the drop.
- Place one edge of the coverslip against the slide, next to the specimen. Gently lower the coverslip over the specimen at a 45-degree angle, allowing the air to escape as it closes.
- Remove any excess water from the sides with a paper towel (if applicable).
Smear Mount
Smear mounting is a technique used to prepare a microscope slide by spreading a small amount of a specimen across the slide.
Unlike a wet mount, where the specimen is suspended in a drop of liquid, a smear aims to create a thin film of the material directly on the slide.
Smear mounting is best for examining individual cells within a fluid or semi-fluid sample, allowing for clear observation of cell morphology and identification of different cell types.
Examples:
- Blood smears: Used to examine red blood cells, white blood cells, and platelets.
- Bacterial smears: Essential for Gram staining and identifying bacteria.
- Cheek cell smears: A common educational activity to view epithelial cells.
- Yogurt smears: To observe the bacteria used in yogurt production.
Steps:
- Create the smear
- For liquid samples: Use a sterile dropper or pipette to place a small drop of the liquid sample near one end of the slide
- For solid samples: Place a small drop of sterile water or saline solution in the centre of the slide. Using a sterile inoculation loop, pick up a tiny amount of the solid sample and gently mix it into the water/saline drop, creating a slightly cloudy suspension.
- Hold a second clean slide (spreader slide) at a 45-degree angle to your sample slide. Touch the spreader slide’s edge to the drop. Then, quickly push the spreader slide across to create a thin, even film that feathers out.
- Allow the smear to air dry completely.
- Heat Fix (optional, but recommended for bacteria)
- Once air-dried, briefly pass the slide (smear-side up) through a flame a few times to help bacteria adhere. Skip for non-bacterial samples.
- Place one edge of the coverslip against the slide, next to the specimen. Gently lower the coverslip over the specimen at a 45-degree angle, allowing the air to escape as it closes.
Staining a Sample
Staining is like adding colour to a black-and-white drawing! It makes the tiny details of your specimen much easier to see under the microscope.
Stains are special dyes that stick to different parts of cells and tissues, highlighting their structures and making them stand out such as a nucleus in eukaryotes.
Common Stains used in Microscopy
The method you would use to stain a sample depends on your specimen and which of its structure(s) you hope to highlight.
Methylene Blue: A good all-purpose stain for animal cells (like cheek cells) and bacteria. It stains nuclei and other acidic parts blue.
Iodine: Commonly used for plant cells (e.g. onion skin) to stain carbohydrates. It turns dark blue or black in the presence of starch.
Crystal Violet: Primarily used to classify bacteria in gram stains by staining them purple.
Eosin Y: Used on plants and animal specimens (such as red blood cells). Stains cell membranes, cytoplasm and extracellular structures either red or pink.
Toluidene Blue: Used to demonstrate mitosis in plant cells by staining acidic cell structures (e.g. nuclei) dark blue.
For example, this is how you would stain bacterial samples with a methylene blue stain:
- Follow the steps for creating a smear mount (as described earlier), including air drying and eat fixing.
- Place the slide on a staining rack and completely cover the smear with methylene blue solution.
- Let the stain sit for 1-3 minutes
- Gently rinse the slide with distilled water to remove excess stain. Tilt the slide and let the water run over the smear, not directly onto it.
- Carefully blot the slide dry with blotting paper before allowing it to air dry completely.
Once your bacteria sample has been stained correctly, the stainable structures of each cell should appear blue.
Now that you know how to prepare slides, what will you explore first? Grab your microscope and start discovering the amazing details hidden all around you!