Targeting contrast agent for magnetic resonance imaging (MRI). 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 (MRI) 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.
