Fig. 8.

The “gatekeepers” of Z-MSN and the structural model of MSN-HA-SiO₂-TSA/DMA. (A) The carboxylic groups and quaternary amino groups were anchored on the surface of Z-MSN to keep DOX in the caves under the physical condition. And the “doors” would be open after hydrolysis of their carboxylic groups in tumor microenvironment. (B) During the blood circulation, the outermost mix-charged zwitterionic layer could keep away from biomolecules with their dense hydration shell. While the pH decreased from 7.4 to 6.5, the surface charge would shift to cationic hence to promote cellular uptake. After the second GSH-sensitive layer taken off in cytoplasm by GSH with high concentration, the innermost FITC-HA layer would be degraded by HAase to release the therapeutics quickly. And the whole process could be tracked in real-time by fluorescence.