Stains and dyes play a critical role in tissue-based diagnosis and research. Stains are temporary, whereas dyes are permanent and can only be removed after cell wall destruction. Dyes are organic unsaturated cyclic compounds which are made up of a chromophore and an auxochrome group. The chromophore is responsible for the specific color of the dye, and the auxochrome group causes the dyeing property of the salt formation. Often dyes require the addition of a mordant to improve the fastness of the dye to the substrate. Stains are biological coloring agents that are purer and prepared with greater specifications than dyes. The electrical charges of the chromagen portions of the both the stain and the cellular components determine the ability of the stain to bind to and stain macromolecular cellular components.
Stains and dyes serve multiple purposes in histology and hematology. They provide contrast to biological tissue, enhancing visualization of cells or cellular components and enabling researchers to view tissue morphology and structure. Stains and dyes can be used to examine bulk tissues, cell populations, or organelles within individual cells. Furthermore, stains and dyes can be used to differentiate not only between live and dead cells but also between different types of organisms. Finally, stains and dyes can aid in the detection of certain features, metabolic processes, and cell types or organelles.
Before the addition of the stain/dye, a solvent is used to remove wax from the slide in a process called de-waxing. Following completion of staining, a coverglass is added to the section to make the stain permanent.
Below are some examples of popular staining techniques utilized by researchers:
- Simple staining uses only one dye. Commonly used dyes for simple staining that are available on Zageno include methylene blue, gram safranin, and gram crystal violet.
- Differential staining uses more than one chemical stain to differentiate between micro-organisms, or structures and cellular components of an individual organism. Gram staining, which is an example of differential staining, uses two stains are to distinguish between gram positive and negative bacteria.
- Routine staining, which is the most common method of staining, reveals underlying tissue structures and conditions. Routine stains are made up of hematoxylin and eosin (H&E) which are basic and acidic dyes, respectively.
- Counterstains make the stained structure more visible by staining with a color contrasting to the principle stain.
- Silver staining is an important technique for visualizing proteins, DNA, and substances inside and outside of cells. This method uses silver to stain histologic sections.
- Papanicolaou staining is used to examine cell samples from various bodily secretions.
- Masson’s Trichrome is a three-colour staining method frequently used in histology. It distinguishes cells from surrounding connective tissue.
An extensive range of stains and dyes are available on Zageno, including the popular choices of Coomassie brilliant blue, DAPI and ethidium bromide solution. When selecting the most appropriate dye for your experiment, remember that the composition of dyes frequently varies between suppliers. Most dyes are available as certified strains, meaning that following extensive testing, they have been found to reach and exceed expectations of dye content, purity, and performance in staining methodologies. The use of certified stains is recommended as it reduces the likelihood of obtaining unexpected and inaccurate results.