Fig. 1: Chemical mechanism schematics for the nanomedicine FHPG for tumor therapy.

After accumulation into tumor region and internalization by cancer cells, the acidic environment enables the degradation of Fe-HMSN-PEG nanocarrier by breaking the Fe–O bond in the –Si–O–Fe– hybrid framework, promoting the co-releases of framework-doped Fe3+ and hollow core-loaded gallate (GA4−) in the nanocarrier into the medium. Thereby, the released GA4− will chelate free Fe3+ spontaneously to form a nano-dimensional coordination complex in situ, which is a qualified electron donator due to the strong metal–ligand coordination. The unique ligand field around the Fe centers of GA–Fe nanoparticles promote ORRs and generate highly oxidizing •OH, finally triggering oxidative damage to tumor.