Magnetic resonance imaging (MRI) technique is at the forefront of biomedical and clinical imaging. Its superb spatial resolution, noninvasive nature and use of benign radiation outweigh its intrinsic low detection sensitivity. However paramagnetic relaxers (called MRI contrast agents) can enhance dramatically the contrast between healthy and diseased tissues by shortening the relaxation times of the water protons in their vicinity. In recent years, extensive attempts have been applied towards new contrast agents with higher molar relaxivity and higher specificity. In this work with the aim of increasing relaxivity, several novel dinuclear Gd-based MRI contrast agents are synthesized. These systems possess two chelating groups per functional unit. An aromatic linker is used to join the chelating parts and the functional unit. This will increase the rigidity of systems and therefore their relaxivity. The functional units are chosen based on their application for different purposes. In all cases, the DTTA (H4DTTA = diethylenetriaminetetraacetic acid) was introduced as chelating ligand for Gd3+. This unit is fairly easy to synthesize and its Gd-complex has two inner sphere water molecules The second chapter deals with the development of a novel DTTA-based contrast agent which is capable of binding human serum albumin (HSA). Two DTTA chelators are bound to the rigid carbazole molecule as well as a biphenyl group which is aimed to bind to HSA. As a consequence of rigidity and the strong binding to the protein, a high relaxivity is obtained. The third chapter is aimed to synthesize two novel dinuclear surfactant molecules which possess again two DTTA as chelating units. Because of the long hydrophobic chain, depending on the concentration, they can aggregate into micellar form in aqueous solutions. Chapter IV is devoted to the synthesis and characterization of gold nanoparticles functionalized with Gd3+-DO3A-N-α-aminopropionate. This novel system with a fast water exchange is prepared and characterized as a new high relaxivity contrast agent potentially safe for in vivo application. In chapter V, compound [Gd4bipy(DTTA-derivative)4(H2O)8]4- is synthesized and characterized. This two-functionalities ligand contains four DTTA derivatives as chelating units for Gd3+, and a bipyridine unit for coordination to Fe2+. This self-assembly heterometallic compound could bring twelve Gd3+ ions together around one Fe2+ core.