Upconversion-Magnetic Carbon Sphere for Near Infrared Light-Triggered Bioimaging and Photothermal Therapy

Nanoparticle-based theranostics combines tumor imaging and cancer therapy in one platform, but the synthesis of theranostic agents is impeded by chemical groups on the surface and the size and morphology of the components. Strategies to construct a multifunctional platform for bioimaging and photothermal therapy (PTT) are urgently needed. A new upconversion-magnetic agent (FeCUPs) based on hollow carbon spheres, which is both a photothermal agent and a dual carrier of luminescent and magnetic nanoparticles, provides an effective approach for tumor elimination. Methods: The morphology of FeCUPs was characterized for the construction and size adjustment of the theranostic agent using transmission electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectroscopy and high angle annular dark field scanning transmission electron microscopy. The distribution of FeCUPs was tracked under in-situ upconversion luminescence (UCL) imaging and magnetic resonance imaging (MRI) in vivo. Photothermal therapy was carried out on tumor-bearing mice, after which the toxicity of PTT was evaluated by a blood biochemistry test and histological section analysis. Results: Stable and uniform loading of luminescent nanocomposites on three-dimensional carbon materials is reported for the first time. Based on the mechanism of synthesis, the size of the hybrid particles was adjusted from micrometers to nanometers. External magnetic field-enhanced photothermal therapy with multi-model imaging was accomplished using FeCUPs. Moreover, no cancer recurrence was found during 14 days of recovery without PTT. Conclusions: Hollow carbon spheres, photothermal agents loaded with upconversion nanoparticles inside and magnetic nanoparticles outside were prepared for photothermal therapy. The aggregation of FeCUPs in tumors by the local magnetic field was verified by MRI and UCL imaging, and PTT was enhanced.