counterstain

/ˈkaʊntərˌsteɪn/
noun
  1. A dye used in microscopy to color parts of a specimen that are not stained by the primary stain, making details easier to see.
    • Without a counterstain, the bacteria were invisible under the microscope.
    • The lab technician applied a counterstain to highlight the cell nuclei.
    • Eosin is a common counterstain used in histology to color the cytoplasm.
Synonyms
verb
  1. To apply a secondary stain to a microscope specimen to reveal additional details.
    • She counterstained the bacteria with a red dye to make them stand out.
    • The biologist counterstained the tissue sample to show both the cell walls and the nuclei.
    • You should counterstain the slide after the primary stain to improve contrast.
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