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The negatively charged cell wall of many microorganisms attracts the positively charged chromophore which causes the specimen to absorb the stain giving it the color of the stain being used. Positive staining is more commonly used than negative staining in microbiology. The different types of positive staining are listed below. [1]
Gram-positive cells have a thick layer of peptidoglycan in the cell wall that retains the primary stain, crystal violet. Gram-negative cells have a thinner peptidoglycan layer that allows the crystal violet to wash out on addition of ethanol. They are stained pink or red by the counterstain, [3] commonly safranin or fuchsine.
In contrast, basic dyes are used to stain cell nuclei and some other acidic components of tissues. [8] Regarding cellular structures, acid dyes will stain acidophilic structures that have a net positive charge due to the fact that they have a negatively charged chromophore. Acidophilic structures include the cytoplasm, collagen and mitochondria ...
A "vital dye" or stain is a dye capable of penetrating living cells or tissues without causing immediate visible degenerative changes. [26] Such dyes are useful in medical and pathological fields in order to selectively color certain structures (such as cells) in order to distinguish them from surrounding tissue and thus make them more visible ...
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[2] [3] Carbol fuchsin is used as the primary stain dye to detect acid-fast bacteria because it is more soluble in the cells' wall lipids than in the acid alcohol. If the bacteria is acid-fast the bacteria will retain the initial red color of the dye because they are able to resist the destaining by acid alcohol (0.4–1% HCl in 70% EtOH). [4]
It is used as a food coloring, [4] printing ink, [5] biological stain, [6] dental plaque disclosing agent, [7] radiopaque medium, [6] sensitizer for orthochromatic photographic films, and visible light photoredox catalyst. [8] Erythrosine is commonly used in sweets such as some candies and ice pops, and even more widely used in cake-decorating ...
Reading the label. You can tell a lot from the design and color of food packaging. The color of a packet of M&Ms, for example, can tell you whether they’re peanut, regular, crispy or caramel ...