CAT and cancer: The high content of GSH in the cytosol of 4T1 cancer cells led to the cleavage of ssmPEG and the exposed TPP consequently guided the Fe3O4 nanozymes to mitochondria to exert CAT‐like activity, producing O2 for PpIX‐mediated 1O2 generation.[27b] The precise intracellular localization controlled by surface modification and external stimuli took full advantage of the dual enzyme‐like activities of Fe3O4 nanozymes.