A cell-permeable, fluorescent dye that accumulates in acidic organelles in a pH-dependent manner and is used for autophagy detection and cell cycle determination; emits green fluorescence (ex. max: 502 nm; ,em. max: 525 nm) at neutral pH or when bound to dsDNA and red fluorescence (ex. max: 460 nm; em. max: 650 nm) at acidic pH or when bound to ssDNA or RNA.