Novel N-RES agents for use in vitro and in vivo medical and biological applications, such as, for example MRI and/or intravenous administration of pharmaceutical agents are described. The novel N-RES agents are prepared by coating inorganic core particles with a poly(acrylic acid) - poly(alkylene ether) graft copolymer. The resulting polymer-coated inorganic particle cores are useful as imaging agents, therapeutic agents or carriers having increased circulation time due to decrease uptake or recognition by the RES.