(706d) PLGA-Encapsulated Graphitic Carbon and Iron Oxide Nanoparticles for Simultaneous Fluorescence and MRI Imaging

There has been considerable interest in recent years in the development of multimodal contrast agents. In particular, the combination of magnetic and fluorescent imaging has attracted attention because of the possibility of combined magnetic resonance imaging (MRI) and fluorescent histopathology or MRI and intrasurgical fluorescence imaging. However a major stumbling block in the implementation of such probes is the toxicity of the fluorescent molecules employed (e.g. quantum dots). We have combined fluorescent carbon and iron oxide nanoparticles in poly(lactic-co-glycolic) acid (PLGA) to produce biodegradable micro/nano-particles that can be used for fluorescent and magnetic imaging, as well as drug delivery. Graphitic carbon nanoparticles of < 5 nm diameter were generated from carbon soot, and exhibited fluorescence originating from nitrogen vacancy centers that give rise to an emission peak at 465 nm. The quantum yield was comparable with that of water soluble cadmium sulfide quantum dots. Iron oxide nanoparticles ~10 nm in diameter were produced through aqueous co-precipitation. Both nanoparticles were embedded in PLGA nanospheres through a double emulsion process. Initial experiments with non biofunctionalized PLGA spheres have shown non-specific endocytosis into human SK-N-SH and glioblastoma cells (neural cell lines). These particles could be used for multimodal imaging. For example, two photon excitation with Ti: Sapphire or Nd:YAG lasers with excitation wavelengths greater than 900 nm would permit fluorescence images from deep tissues. These images could then be correlated to those from obtained from MRI images, enhancing the ability to obtain weighted images.