In this study, we developed a new bimodal imaging tracer directed against endothelin B receptors to detect brain cancer cells with MRI and to assist tumors surgery with fluorescence imaging. This was achieved by coating the surface of iron oxide nanoparticles with a monoclonal antibody, rendomab-B1, labeled with fluorescent dye. Two nanoplatforms were elaborated differing by the average number of antibodies grafted onto nanoparticle surface. The targeting efficiency of these nanoplatforms was validated in vitro. Contrasting MRI properties were highlighted in vivo, demonstrating nanoparticle circulation in the brain through the vasculature.