Scheme 1. (a) The “turn on” fluorescence of GC–NABP in the presence of H₂O₂ and a schematic illustration of the self-assembled GC–NABP nanoprobe for targeted imaging in vivo. (b) Targeted imaging of H₂O₂ in a tumor cell with the GC–NABP nanoprobe in an acidic tumor microenvironment. (c) Scheme of GC–NABP nanoprobe in normal physiological fluids.