Staining techniques
Most cells are almost transparent and it is very hard to distinguish any structures. To better visualize cells and their specific components you can use chemicals that stain certain structures. H&E is the most widely used stain in medical diagnosis. Hemalum, a complex formed from aluminum ions and hematein, stains nuclei and some other cell components blue. A second stain follows the nuclear-staining, the E in H&E. Eosin is an acidic dye that likes to connect to basic structures and stains the cytoplasm and extracellular proteins pink. Most stains require some sort of preparation to allow the stain to penetrate the cells. Most of these methods kill the cells, hence light microscopy is not ideal to visualize processes in living cells.
Usually one or several of the following procedures is required to stain cells:
-
Dehydration - Replacing the water within the sample with some other chemical
-
Permeabilization - dissolving cell membranes to allow lager dyes to penetrate the inside of the cell
-
Fixation - invloves several techniques, such as creating chemical bonds between proteins to increase their rigidity.
-
Mounting - attaching samples to the microscopy slide.
-
Mordant application - a substance that forms a strong complex with the dye and the tissue
The Mallory staining method used in our example makes use of three different dyes. This method has the advantage of visualizing a larger number of tissue structures. Mallory stain combines aniline blue (connective tissue, extracellular matrix, glycoproteins, and mucus), orange G (proteins), and the dark red fuchsin (RNA and DNA).
Crypt of Liberkühn stained with the three Mallory dyes