targeting contrast agent for magnetic resonance imaging . in preferred embodiments , self - assembled polyelectrolytes coated superparamagnetic iron oxide contrast agent particles are provided , which are labeled with targeting moieties , afforded enhanced relaxivity , improved signal - to - noise and targeting ability . accordingly , the invention relates to a stable targeting contrast nanosystem applicable for magnetic resonance imaging having at least one nanoparticle polyelectrolyte polyanion ; a targeting agent conjugated to the biopolymer ; and a superparamagnetic ligand . in another embodiment the nanosystem according to the invention has at least two biocompatible and biodegradable nanoparticle polyelectrolyte biopolymer . particularly , the superparamagnetic iron oxide particles are coated by a polyelectrolyte biopolymer and this system self - assembles with the other biopolymer to produce stable nanosystem for magnetic resonance imaging . targeting moieties are conjugated to a biopolymer or to the self - assembled biopolymers to realize a targeted delivery of contrast agent . methods for making these targeting mri contrast agents are also provided .