Incorporation of Graphene Quantum Dots, Iron, and Doxorubicin in/on Ferritin Nanocages for Bimodal Imaging and Drug Delivery

Abstract Graphene quantum dots (GQDs) have been emerging as next‐generation bioimaging agents because of their intrinsic strong fluorescence, photostability, aqueous stability, biocompatibility, and facile synthesis. In this work, GQDs are encapsulated in ferritin protein nanocages to develop multi‐functional nanoplatforms toward multi‐modal imaging and cancer therapy. Encapsulation of ultra‐small GQDs is expected to reduce their quick excretion from the body and increase their bioimaging efficiency. To expand the functionality of protein nanocages as multi‐modal imaging nanoprobes capable of both fluorescence and magnetic resonance imaging (MRI), GQDs and iron are encapsulated inside the core of AfFtn‐AA (an engineered ferritin nanocage derived from the archaeon Archaeoglobus fulgidus ). The co‐encapsulation is achieved through an iron‐mediated, self‐assembly of ferritin dimers resulting in the formation of GQD–iron complex in the ferritin nanocages ((GQDs/Fe)AA). The (GQDs/Fe)AA shows high relaxivities in MRI and pH‐sensitive fluorescence with strong fluorescence at low pH values and on MDA‐MB‐231 cells. As an imaging agent and a drug nanocarrier, (GQDs/Fe)AA exhibits negligible cytotoxicity on the cells and a high loading capacity (35%) of doxorubicin. Taken together, the (GQDs/Fe)AA shows promising applications in cancer diagnosis and therapy as a pH‐responsive fluorophore, MRI agent, and drug nanocarrier.