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The purpose of this study was to develop a bifunctional iron oxide (IO) nanoparticle probe for PET and MRI scans of tumor integrin α_vβ₃ expression. Polyaspartic acid (PASP)–coated IO (PASP-IO) nanoparticles were synthesized using a coprecipitation method, and particle size and magnetic properties were measured. A phantom study was used to assess the efficacy of PASP-IO as a T2-weighted MRI contrast agent. PASP-IO nanoparticles with surface amino groups were coupled to cyclic arginine-glycine-aspartic (RGD) peptides for integrin α_vβ₃ targeting and macrocyclic 1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″,-tetraacetic acid (DOTA) chelators for PET after labeling with ⁶⁴Cu. IO nanoparticle conjugates were further tested in vitro and in vivo to determine receptor targeting efficacy and feasibility for dual PET/MRI. PASP-IO nanoparticles made by single-step reaction have a core size of …