Used as a fluorescent stain in microscopy and flow cytometry to detect dead cells. It binds to DNA but cannot cross intact cell membranes, so it only enters cells with damaged membranes, marking them as non-viable. Commonly used in cell viability assays, apoptosis studies, and cell cycle analysis. Also applied in bacterial biofilm visualization and plant protoplast analysis. Its fluorescence increases significantly upon binding to nucleic acids, making it useful for quantifying DNA content in fixed cells.