Introduction: Brain tumor margin detection remains a challenging problem in the operative resection of gliomas. A novel nanoparticle, a PEGylated quantum dot, has been shown to be phagocytized by macrophages in vivo. This feature may allow quantum dots to co-localize with brain tumors and serve as an optical aid in the surgical resection of brain tumors. Methods: Sprague-Daly rats were injected intracranially with C6 gliosarcoma cell lines to establish tumors. Two weeks after implantation of brain tumors, PEGylated quantum dots emitting at 705 nm (PEG-705 QD) were injected via the tail vein. Twenty-four hours post PEG-705 QD injection, the animals were sacrificed and their tissues examined. Results: PEGylated quantum dots are avidly phagocytized by macrophages and are taken up by liver, spleen and lymph nodes. Macrophages and microglia co-localize with glioma cells, carrying the optical nanoparticle, the quantum dot. Excitation of the PEG-705 quantum dots gives off a deep red fluorescence detectable with charge coupled device (CCD) cameras, optical spectroscopy units, and in dark field fluorescence microscopy. Conclusions: PEG-705QDs co-localize with brain tumors and may serve as an optical adjunct to aid in the operative resection of gliomas. The particles may be visualized in surgery with CCD cameras or detected by optical spectroscopy.