Photoluminescent and superparamagnetic reduced graphene oxide–iron oxide quantum dots for dual-modality imaging, drug delivery and photothermal therapy

Reduced graphene oxide–iron oxide quantum dots (QDs) with intrinsic photoluminescent and superparamagnetic properties were synthesized through a green, hydrothermal method that simultaneously reduced and shattered graphene nanosheets to form the dots. The structure, morphology, properties and cell viability of these QDs were investigated. The QDs emitted violet light when excited at 320 nm, possessed no residual magnetization upon magnetic hysteresis tests, and had low cytotoxicity to healthy cells at low concentrations. The suitability of the QDs for fluorescent and magnetic resonance dual-modality imaging was shown by in vitro imaging with dermal fibroblast cells and T2 relaxation time. A drug could be loaded onto the surface of the QDs, with a loading ratio of drug to QD of 0.31:1. The drug achieved a steady but full release from the QDs over 8 h: these drug-loaded QDs could be manipulated by an external magnetic stimulation for targeted drug delivery. The potential for use as a cancer photothermal therapy was demonstrated by both a rapid, ∼50 °C temperature increase by a suspension of 100 μg ml−1 of QDs and the photothermal ablation of HeLa cells in vitro under near infrared irradiation. The stability of the MGQDs in fetal calf serum was shown to improve when an ionic drug was coated on the surface.