Hint: The process which helps in increasing contrast in samples is known as staining. It is used to increase visibility or to improve the level of distinction of specimen in microscopic levels. It is mostly carried out in microbiology and histology. There are different kinds of staining procedures specific for each specimen to be visualized.
Complete answer: A stain is a chemical dye which is utilized for colouring biological materials. Stains are organic compounds consisting of two components, the chromophore that imparts colour to the stain as well as the auxochrome group. There are mainly four different kind types of stains:
1. Differential stain: Chemical that can bind to different structures or organisms in different manners. Eg: Ethanol, crystal violet, Gram’s iodine. 2. Simple stain: Where the dye or stain is nonspecific and stains all the features and entities of the specimen. Eg: Safranin, methylene blue. 3. Negative stain: Type of stain that stains the background but does not stain the specimen. Eg: India ink, nigrosine. 4. Special stain: Dye that has the ability to stain particular minute subcellular structures. Eg: Biebrich Scarlat stain has the ability to stain muscles and collagen.
Note: Stain molecules can be of two types- acidic and basic. Acidic stains are utilized for background staining whereas basic stains are used for staining bacterial cells. There are predominantly two types of staining techniques- simple and differential staining. Simple stain utilizes a single dye or stain, whereas differential staining technique utilizes two contrasting stains simultaneously. An example of differential staining is gram staining.