Fixed cells have been preserved by a fixation step that “locks” the cell in place. They provide a static snapshot into cellular function. While cellular composition is compromised, larger structures such as proteins, organelles and DNA are conserved. The fixation process kills the cells, which makes the outside cell membrane more permeable than living cells. As such, it becomes easier to target internal cellular structures with dyes and antibodies. Imaging fixed cells allows high-resolution imaging of sub-cellular structures.
However, fixed (dead) cells cannot provide dynamic insights into biological function and do not represent living systems. Live-cell imaging occurs while cells are alive. If imaged over time, real-time dynamic data can be collected and events that could be missed with endpoint, fixed cell assays are captured.