Staining Techniques in Microscopy

Study Notes

Stain: A substance that adheres to a cell, giving it color. Color provides contrast, making cells more visible under a microscope.
Dye: Synthetic stains.
Pigment: Stains extracted from plants or animals.
Staining Technique: A microscopy method for enhancing contrast in images.

Origin:
- Animal origin (e.g., carmine from insect bodies).
- Plant origin (e.g., hematoxylin from the Mexican tree).
- Synthetic (e.g., eosin).
Mode of action:
- Physical staining: The stain physically combines with the structure by absorption. (e.g., Sudan III, stains fats orange-yellow).
- Chemical staining: The stain chemically reacts with the structure (e.g., various stains for DNA).
End color of stained content:
- Orthochromatic: The stain reacts with the cell content, resulting in the same color. (e.g., cytoplasm with methylene blue gives a blue color).
- Metachromatic: The stain reacts with the cell content and produces a different color. (e.g., starch with iodine solution gives a blue color).
- Metachromasia: The reaction between the stain and the content results in a color different from the stain's original color.

Number of stains used:
- Monochromatic (simple): Uses one dye.
- Polychromatic (multiple): Uses several dyes. Multiple dyes allow different structures to be stained in different colors (e.g., trichrome stain uses three dyes for color differentiation).
Nature of stained material:
- Staining in toto: Staining the entire tissue mass.
- Section staining: Staining sections of the tissue. This method firstly sections the specimen, and then stains the separated sections.
Applied method:
- Regressive: Over-staining followed by removal of excess stain to reach the desired intensity.
- Progressive: Sections are gradually stained until the desired intensity is reached.
- Mordant use: Using a mordant to fix the stain better to the tissue. The mordant is a chemical that aids stain fixation and helps in more intense coloring. (e.g., in Gram staining and iodine solution procedure for crystal violet)
- Special methods: Specialized methods like fluorescent and electron microscopy.

Stains that can diffuse through living tissues without harming them.
- Intravital: Staining living cells inside the body (in vivo).
- Supravital: Staining living cells outside the body (in vitro).

Acidophilic: Substances that have an affinity for acid stains.
Basophilic: Substances that have an affinity for basic stains.
Eosin stain: A stain that stains cytoplasm, usually pink.
Basic fuchsin: A stain that stains DNA, often creating a pink/purple color.
Neutral Stains: Stains with both acid and base radicals. These stains are utilized in blood cell staining.