Eosin, also known as eosin, is a peach or pink powder with the molecular formula C₂₀H₆O₅Br₄Na₂ and molecular weight of 691.86; clinically, it can be used to evaluate sperm survival by detecting the integrity of the sperm membrane.

Sperm viability staining solution (Eosin method) can routinely test the viability of all sperm specimens, and identify sperm with intact cell membranes by dye rejection staining method, so as to derive the percentage of viable sperm, which consists of Eosin, deionized water and so on, and makes use of the principle of dye rejection staining, that is, the correlation is based on the damage to cell membranes such as the membrane on the non-living (dead) cells, which allows the non-transmissible membrane dyes can be accessed to the membrane to be stained; The cell membrane of living cells is able to resist the entry of dyes, so the phenomenon of dye rejection is produced and no coloring is done.