**6. Neural stem cells functionalized with radiolabeled nanoparticles**

Neural stem cells (NSCs) are increasingly being used as carriers for targeted delivery of therapeutics to glioblastoma. This requires multimodal dynamic in vivo imaging of NSC in the brain. Such type of technology is in development phase. Cheng et al. reported an innovative strategy for neural stem cell tracking in brain using silica nanoparticles via SPECT [33]. 111In radioisotopes were conjugated to porous silica nanoparticles having large surface area. A series of nanomaterial characterization assays were performed to evaluate the modified mesoporous silica nanoparticles. Loading efficiency and viability of NSCs with 111In-MSN complex was validated. Radiolabeled NSCs were administered to glioma-bearing mice via intracranial or systemic injection. SPECT and bioluminescence imaging were performed periodically after NSC injection. Histology and immunocytochemistry were performed to endorse the findings. 111In-MSN complexes showed minimal toxicity to NSCs and adequate in vitro and in vivo stability. Phantom studies establish possibility of mesoporous silica nanoparticles for NSC imaging. It was found that decayed 111In-MSN complexes exhibited significant fluorescent profiles in preloaded NSCs, thus validating ex vivo data. In vivo, SPECT images reveal actively migrating NSCs toward glioma xenografts in real time after both intracranial and systemic injection. This is in consonance with findings of histology, confocal microscopy and bioluminescence live imaging [33].
