Cell Staining is a microscopic technique that is used better visualize cells and their components by highlighting and contrasting them while under a microscopic. Scientists use stains and dyes to preferentially highlight certain components of the cell, such as its cell wall or nucleus or even the entire cell. Staining is usually carried out on fixed, non-living cells but some stains can be used on living cells, or even both.
Cells may be stained to highlight metabolic processes that they are involved or in to differentiate between the dead and the live cells in a sample.
Which cell stain technique is used depends on the type of stain and analysis being used in the lab. A scientist could use any of the following procedures to prepare a stained cell sample.
Permeabilization: The treatment of cells with a mild surfactant (a compound that lowers the surface tension of liquids) which dissolves the cell membranes in order to allow larger dye molecules to enter inside the cell.
Fixation: This process serves to preserve the cell or tissues morphology. The fixation process will involve several steps, but usually a chemical fixative such as formaldehyde, ethanol, methanol or picric acid that is added that creates chemical bonds between proteins that increase their rigidity.
Mounting: Where Samples are attached to a glass microscope slide for observation and analysis. The cells can be grown directly to the slide or loose cells can be applied to it. Thin sections or slices of the material being examined can also be applied.
Staining: The actual application of strain to the slide and the sample on it. The Cells, metabolic processes, tissue matter and cell components are all coloured by the strain. Staining is achieved by submerging the sample in a solution of dye and then rinsing and observing the slide under a microscope. Certain dyes require the use of a chemical compound called a mordant, which reacts with the stain to form a coloured, insoluble principate which will remain in the sample when excess dye is washed away.
The Most Popular Stains:
There is a large variety of different staining dyes, each with a different purpose. All of these listed stains can be used on fixed or “non-living cells” and stains that can be used on un-fixed or living cells are noted.
Bismark Brown: Named after the 19th century German statesman, Bismark Brown colors acid mucins (a form or protein) a yellow hue and may be used to stain live cells
Carmine colours glycogen (another name for animal starch) red
Coomassie Blue strains all proteins a very bright blue. It is often used in gel electrophoresis
Crystal Violet stains cell walls purple (hence its name) when combined with a mordant. It is used in Gram staining
DAPI is a fluorescent stain that shines blue when it is affected by ultra violet light and bound to DNA. DAPI can be applied on both living and fixed cells.
Eosin is a counter-stain to haematoxylin. Eoisin stains red blood cells, cytoplasm, cell membranes and extracellular structures red or pink.
Ethidium Bromide colours unhealthy cells during the stage of apoptosis, deliberate cell death, a fluorescent reddish orange.
Fuchsin is used to stain collagen, smooth muscle and mitochondria
Hematoxylin is a nuclear stain that when acting with a mordant, stains nuclei brown or a bluish violet
Hoechst stains are two different types of stains used to colour DNA in living cells
Iodine is used as a starch indicator which creates a dark blue coloured stain when in solution
Malachite green is a blue/green counterstain to safarnin. It is used to stain spores.
Methylene blue stains animal cells to better visualize their nuclei
Neutral/Toluylene red colours nuclei red and can be used on living cells
Nile blue can be used on living cells and stains cell nuclei blue
Nile Red and Nile Blue Oxazone is a stain made by boiling Nile blue with sulfuric acid creating a mixture of Nile Red and Nile Blue. Nile Red stains intracellular lipid globules and can be used on non-fixed, living cells.
Osmium tetroxide is used in optical microscopy to highlight lipids black
Rhodamine stains proteins fluorescent
Safranin is used to stain collagen yellow
After stained and prepared, the cell slides must be stored in a dark and possible refrigerated place to preserve the slide in between being observed under a microscope.