PGP and cancer: Like iron oxide nanoparticles, QDs can also be engineered as drug delivery platforms for delivering siRNAs and anticancer drugs by the surface modification.90 For instance, Li et al. developed L‐Arg or L‐His modified beta‐cyclodextrin (β‐CD) coated with CdSe/ZnSe QDs to simultaneously deliver DOX and P‐gp targeted siRNA to reverse the MDR HeLa cancer cells.91 Dox can be loaded into the hydrophobic parts of β‐CD, while the P‐gp related siRNA was absorbed onto the surface of QDs by electrostatic interaction between the positive charging L‐Arg/L‐His with the negative charging siRNA (Figure4A).