propidiumjodide

Propidium iodide, often abbreviated as PI, is a fluorescent intercalating agent that is commonly used to detect cells in flow cytometry and fluorescence microscopy. It is a membrane-impermeant dye, meaning it cannot cross the plasma membrane of living cells. This property makes it useful for distinguishing between viable and non-viable cells. When a cell dies, its membrane integrity is compromised, allowing propidium iodide to enter the cell and bind to its DNA. Once inside the nucleus, PI intercalates into the DNA double helix, specifically between G and C bases. Upon excitation with light at a wavelength of approximately 535 nm, propidium iodide emits fluorescence at a peak emission of around 617 nm, which is in the red spectrum. This red fluorescence can then be detected by appropriate filters in flow cytometers or fluorescence microscopes. Due to its red emission, it is often used in conjunction with green fluorescent dyes like fluorescein isothiocyanate (FITC) or green fluorescent protein (GFP) that emit in the green spectrum. This dual-staining approach allows researchers to simultaneously identify and quantify both dead (PI-positive) and live (PI-negative) cell populations within a sample. Propidium iodide is typically dissolved in a buffer solution before use. It is important to note that propidium iodide is a mutagen and should be handled with appropriate safety precautions.