(747a) Carbon-Iron Oxide Fluorescent-Magnetic Nanocomposites for In Vivo Imaging

Here we present the design, synthesis, and evaluation of fluorescent-magnetic nanocomposites for in vivo, multimodal, brain tumor imaging. One of the primary limitations in brain tumor resection is difficulty distinguishing normal from cancerous tissue. Whereas this can be achieved to some extent via pre-operative MRI, there is a need for intra-operative tumor imaging technologies. In particular, it is desirable to have multifunctional imaging agents, which not only allow non-invasive pre-operative magnetic resonance imaging (MRI), but also direct tumor observation through fluorescence imaging during surgery. We are investigating carbon dots (C-dots) as potential, bright, photostable, and non-toxic fluorescent imaging agents in composites with superparamagnetic iron oxide nanoparticles (SPIONs), which, for some thirty years, have been utilized extensively as contrast agents for MRI. These multimodal nanocomposites, consisting of both fluorescent C-dots and SPIONs, are encapsulated in polymer nanosphere matrices made of poly (lactic-co-glycolic acid) (PLGA), yielding a dual functional imaging contrast agent that responds to both fluorescent and magnetic stimuli.

Fluorescent C-dots (diameter of 2 – 5 nm) whose quantum efficiency was ~ 2.6 %, were synthesized by acid reflux of non-fluorescent and commercially available carbon black. According to results obtained via Raman spectroscopy, this precursor material was graphitic in nature. Previous studieson the toxicity of other carbonaceous materials such as fullerenes and carbon nanotubes, have shown low levels of toxicity. Using preliminary MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) evaluations, we detected low levels of toxicity in C-dots. An aqueous suspension of SPIONs was prepared from a mixture of iron (II) chloride tetrahydrate and iron (III) chloride hexahydrate, heated to 70 °C, and treated with a concentrated solution of sodium hydroxide. C-dots and SPIONs were incorporated into PLGA nanospheres by following a double emulsion procedure. This yielded PLGA nanocomposites ranging from 100 to 200 nm, which were not able to non-specifically bind to brain cancer cell lines. We also investigated the specific targeting of these cell lines by successfully conjugating PLGA-encpasulated C-dots-SPIONs nanocomposites to interleukin 13 receptor (IL-13R) antibodies using standard EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) chemistry.

This research will broaden and improve in vivo imaging tools necessary for the location and surgical resection of brain tumors. These tumors, in spite of dramatic improvements in micro-neurosurgical techniques, neuroimaging, chemotherapy, and radiation therapy, remain very difficult to treat. Maximal surgical resection has been shown to be a critical factor in extending survival of patients suffering from these lesions. Our multifunctional nanocomposites will allow the selective targeting of brain tumor cells, as well as their detection by both diagnostic MRI and intraoperative fluorescence imaging. Thus, surgical resections are expected to improve, and patient survival will be extended.