Widely used in fluorescence microscopy and flow cytometry to stain DNA in live and fixed cells. It binds to the minor groove of double-stranded DNA, showing strong blue fluorescence when excited by UV or violet light. Commonly applied in cell cycle analysis, apoptosis detection, and nuclear visualization due to its high membrane permeability and low cytotoxicity. Also used in dual staining protocols with green fluorescent dyes like calcein-AM or FITC for simultaneous assessment of cell viability and nuclear morphology. Suitable for in vivo imaging in some model organisms because of its ability to cross cell membranes and label nuclei without immediate cell damage.