Propidium iodide is widely used in biological research for staining cells to assess cell viability and in cell cycle analysis. It is particularly effective in distinguishing between live and dead cells due to its ability to penetrate compromised cell membranes, which are characteristic of dead or dying cells. Once inside the cell, it binds to DNA by intercalating between the bases, emitting a strong red fluorescence when excited by specific wavelengths of light. This property makes it a valuable tool in flow cytometry and fluorescence microscopy for analyzing cell populations and determining the percentage of dead cells in a sample. Additionally, it is employed in studies involving apoptosis and necrosis to monitor cell death processes. Its use is also common in plant biology for analyzing pollen viability and in microbiology for evaluating bacterial cell integrity.