In this study, inspired by the MRET principle, a novel tumor microenvironment (TME)-activated T1- and T2-dual-mode MRI nanoswitch was designed using platelet-derived growth factor (PDGFB)-conjugated ferroferric oxide coated by Mn-doped silica (FMS) yolk-shell nanostructures (PDGFB-FMS) (Scheme 1), which display a distinct "off–on" T1–T2 dual-modal synergistic imaging with an ultrafast response, high sensitivity and specificity toward TME. Here, PDGFB is linked to neoplasm.