What happens when you fix cells?

Cell fixation is essential prior to immunostaining, to fixate permeabilized cells and prevent the cells from collapsing or diffusing, and to retain the life-like shape. Cell fixation is a series of chemical events when the aqueous cell cytoplasm is replaced to non-aqueous solution (fixative), and this includes tissue shrinkage (by 20-30% volume) and hardening of some of the components. During fixation some of the tissue elements chemically react with the fixative, by stabilizing, cross-linking and preserving it. The cell fixation mechanism depends on the reagent used for fixation (e.g. methanol or formaldehyde).