What Is The Function Of A Microscope Slide?

A microscope slide is a thin, rectangular glass plate that holds a specimen. A slide is prepared and then placed on the stage of a microscope for viewing. A microscope slide usually measures 75 by 26 mm (3 by 1 inches) — although they can be supplied as either squares or rectangles — and is available in a range of thicknesses and materials. The purpose of a microscope slide is to act as the support for a sample or specimen which needs to be examined under a microscope. The most important aspects of any microscope slide are the clarity and quality of the glass and the nature of the light which can pass through it.

Types of Microscope Slides

There are different ways to prepare a microscope slide depending on the type of specimen you are viewing. These include:

• Dry mount: A specimen is placed on a slide with or without a coverslip over it. This method is useful for viewing dry specimens such as hair or pollen. These are the easiest slides to prepare — simply adding a dry specimen to a slide and covering it with a cover slip. These work well for specimens such as hair, pollen, an insect wing, or dry skin. One major disadvantage is that they are very temporary and will fall apart easily with no liquid holding the cover to the slide.
• Wet mount: A specimen is placed on a drop of water on the slide, with a coverslip placed over it. This is often used for viewing cells. Adding a liquid helps increase the magnification of the specimen being viewed. A wet mount slide can be prepared using water or oil. These slides may or may not have a cover slip on top, and can also be effective in observing live specimens.
• Prepared slides: This type of slide has already been professionally prepared and can last long-term. A specimen on a prepared slide has been permanently fixed and preserved, usually through heat-fixation, mordant application, and the use of a mounting medium. A mounting medium keeps the specimen preserved and adhered to the slide and coverslip.
• Smears: A smear is a sample that is spread across a slide and allowed to dry. A coverslip may be used in this type of preparation. This technique is helpful for viewing blood samples.
• Concave slides: These concave, or depression, slides differ from flat slides in that they have an indentation to better hold an amount of liquid for viewing and do not require a coverslip. A concave slide is helpful for viewing a liquid sample such as pond water.

Materials Used for Microscope Slides

Materials used depend on the intended application. Microscope slides are available in a range of materials, each offering different properties:

Quartz / UV Fused Silica

Offers enhanced UV transparency, suitable for applications requiring UV light transmission.

Sapphire

Provides the ability to work at high temperatures, used in more demanding laboratory environments.

CaF2

Used for specific optical applications requiring calcium fluoride properties.

Borosilicate

A commonly used glass material offering good optical clarity and chemical resistance for standard laboratory use.

Applications and Uses for Microscope Slides

Microscope slides can be purchased from stock or manufactured to meet specific demands. They are used in the following circumstances:

• University laboratories
• R&D research
• Haemocytometers
• Original equipment manufacturers (OEM) producing high precision optical instruments
• Cytology and histology applications
• Biological research, medical diagnostics, and educational settings for detailed examination of specimens

Specimens placed under a microscope are best viewed on slides. These specimens can be anything from biological tissues to materials, examined under a microscope for analysis. Sometimes the specimen on the slide is a whole organism. Other times it is a thin slice of tissue, or a smear of fluid in which are cells to be observed.

How to Prepare a Dry Mount Slide

A dry mount slide is the easiest to prepare. The only steps needed are to place a specimen on the slide, and then place a coverslip over it if needed. This is easier than preparing a wet mount slide since a liquid is not required and there is no risk of air bubbles that can make it difficult to clearly view the specimen.

How to Prepare a Wet Mount Slide

1. Place the specimen on the slide.
2. Add a drop of liquid to the slide using a dropper pipette.
3. Set one edge of the coverslip on the slide next to the specimen and slowly lower it until it is laying flat. This will help prevent air bubbles, allowing for a clearer view of the specimen.
4. It might be helpful to use tweezers to hold the coverslip as you lower it.
5. Stains may also be applied to help view certain cell structures.

Using Stains on Microscope Slides

Sometimes a stain is necessary to help view cells under a microscope. By staining certain cells, it may be easier to view features such as shape for classification and to see specific cell structures like the nucleus. There are a few different techniques for staining cells:

• Permeabilization: A technique used to allow larger dye molecules into a cell. Since the cell membrane normally blocks larger molecules from entering the cell, a surfactant, or soap, is used to dissolve the cell membrane. This allows the larger dye molecules into a cell to stain internal structures.
• Mordant application: Used to help set stains in a specimen. This helps maintain the dye application during viewing. A mordant is usually a chemical.
• Heat fixation: Heat is applied to help preserve a specimen and attach it to the slide. Heat fixation is often used for bacterial samples and maintains the structure of the cells.

Some common stains include methylene blue, iodine, and crystal violet. For example, methylene blue is very helpful for staining animal cells and making the nuclei more visible. Fuchsin is a dye that adheres to collagen, mitochondria, and smooth muscle fibers, and nile blue is used to stain cell nuclei, even on living cells. Stains are a great way to make otherwise indistinguishable features of cells and tissues stand out and become more visible, and more than one stain can be used at once.

What Are Coverslips and Their Role

Coverslips are flat pieces of glass less than a millimeter thick and generally around 20 mm wide. A coverslip is placed over a specimen on a microscope slide, to hold the specimen in place and protect it from contamination from the environment. At the same time, the coverslip protects the lens of the microscope, stopping it from coming into contact with the specimen. Coverslips are available in a range of materials including 'Z' cut quartz, fused quartz, ITO coated glass, ITO fused quartz, sapphire, borosilicate glass D263M, Schott D263® T eco glass, and UV fused silica.

The Role of the Slide Holder in Microscopy

A slide holder is a device that holds the microscope slides securely in place. It ensures that the slides don't move while you're looking through the microscope. There are different kinds of microscope slide holders, each designed for specific types of microscopy and different user needs:

• Fixed slide holders: These hold the slide in a set position, which is great for simple observations.
• Adjustable slide holders: These allow you to move the slide up, down, or sideways for more precise viewing.
• Rotating slide holders: These let you rotate the slide, which is useful for detailed examinations from different angles.

Proper slide positioning is crucial for clear images. The slide holder ensures the slide is placed correctly under the microscope lens. Optical alignment is all about making sure the microscope's lenses are perfectly aligned to provide sharp images. The slide holder helps maintain this alignment by keeping the slide at the right distance and angle from the lenses. This stability reduces image distortions and improves the overall clarity of what you're viewing.

Standard Glass Microscope Slide in Practice

A standard glass microscope slide holds a plant or tissue section that has been stained and mounted under a cover glass (also known as a coverslip). Prepared slides of tissues can be purchased or made. For example, a cross section of a leaf that has been fixed in alcohol, thinly sliced, stained, and a section mounted in Canada balsam — which hardens and preserves the specimen — can be examined under a light microscope. Thin sections are used to examine both animal and plant cells with a light microscope. It is important to carefully pick up the slide from the sides to avoid fingerprints from getting on it.