– LysoTracker Red (LysoTracker Red DND-99) is a paraformaldehyde fixable probe that concentrates into acidic compartments of cells and tissues. LysoTracker Red is an indicator of cell death in a manner similar to other standard assays (Annexin, terminal dUTP nick end labeling, Nile blue sulfate, neutral red, and acridine orange). LysoTracker Red is a marker for late endosomes and lysosomes.