A nanoparticle composition is provided. The nanoparticle composition includes a plurality of nanoparticles, each nanoparticle of the plurality having a core including tantalum oxide, and a covalent coating covalently bound to the core. The covalent coating includes a surface modifier selected from the group consisting of (3-aminopropyl)trimethoxy silane (APTMS), (3-aminopropyl)triethoxy silane (APTES), APTMS-methoxy-poly(ethylene-glycol)-succinimidyl glutarate (APTMS-m-PEG-glutarate), APTES-methoxy-poly(ethylene-glycol)-succinimidyl glutarate (APTES-m-PEG-glutarate), 2-[methoxy (polyethyleneoxy)-9-12-propyl] trimethoxysilane (PEG-Silane), hexadecyltriethoxy silane, and combinations thereof. Methods of synthesizing and using the nanoparticle composition are also provided.