In certain embodiments this invention provides a nanoparticle-based technology platform for multimodal in vivo imaging and therapy. The nanoparticle-based probes detects diseased cells by MRI, PET or deep tissue Near Infrared (NIR) imaging, and are capable of detecting diseased cells with greater sensitivity than is possible with existing technologies. The probes also target molecules that localize to normal or diseased cells, and initiates apoptosis of diseased cells.