Eosin-Nigrosin is a combination of two dyes, eosin and nigrosin, which is widely used for staining in biological and medical research. This staining combination provides excellent contrast of cellular structures and is particularly useful when studying cells in various fluids or tissues.

Eosin is a red dye that binds to basic components of cells, such as proteins in the cytoplasm and cell organelles. It is often used in combination with hematoxylin to produce what is known as hematoxylin-eosin (H&E) staining. In the eosin-nigrosin combination, eosin is used to stain cell structures in shades of red and pink.

Nigrosin, on the other hand, is a negative dye, meaning it is not taken up by cells and stains the background dark. Nigrosine is often used in combination with other dyes to increase the contrast between cells and the background. In eosin-nigrosin staining, nigrosin provides dark background staining, making the red-stained cells more visible.

Eosin-nigrosin staining is used in various applications, such as the study of cell morphology, cell viability or sperm quality. In sperm analysis, eosin-nigrosin staining is used to distinguish live sperm from dead sperm because live sperm do not absorb the dye, while dead sperm are stained red.