A lysosome-specific fluorescent reporter for the detection of hydroxyl radicals; selectively fluoresces in low pH environments in the presence of hydroxy radicals over hypochlorite, superoxide, nitric oxide, or peroxynitrite radicals; displays lysosomal fluorescence in the presence of erastin or (1S,3R)-RSL3, an effect that can be blocked by ferrostatin-1, in 4T1 cells at 10 µM; ex/em maxima = 510/592 nm, respectively, in low pH environments in the presence of hydroxy radicals