Methylene blue is used to stain animal cells to make nuclei more visible under a microscope. Methylene blue is commonly used when staining human cheek cells, explains a Carlton College website.
Cell staining is useful because it enhances visualization of specific components within a cell. Cell staining can also be used to highlight processes, such as the stages in cell division. Methylene blue is specifically used in staining animal cells and blood film. This staining media works by dyeing the nuclei of cells and making the particular structure more visible under a light microscope. Any tissue that can absorb stains and dyes is referred to as chromatic. Without stains, such as methylene blue, cells appear almost transparent under a microscope. The type of stain used determines the techniques and slide preparations that must be performed; examples include heat fixation, adding a chemical fixative, treatment with a mild surfactant, mounting and immersion into a dye solution. Malachite green, used to stain spores, and iodine, a starch indicator, are other popular dyes used in staining cells. Stained slides can be preserved by storing the slide in a refrigerator or in a dark environment for later observation under a light microscope. Stains can also be used in transmission electron microscopy.