In this paper, we report the synthesis of size-controlled (6 and 18 nm) monodisperse magnetic iron oxide nanoparticles, from the pyrolysis of iron oxyhydroxide with oleic acid in high temperature solvents. Superconducting Quantum Interface Device (SQUID) measurements revealed that the iron oxide nanoparticles exhibit a superparamagnetic behavior at room temperature. In order to evaluate their potential applications as contrast agents in Nuclear Magnetic Resonance (NMR) imaging, we investigated using 1H NMR spectroscopy (at a magnetic field 4.7 T) the changes in $T_1$ and $T_2$ relaxation times in the colloidal aqueous solution at various concentration of nanoparticles. The following transverse ($r_2$) and longitudinal ($r_1$) relaxivities were found: ($r_2 = 17.85 mM^{-1}s^{-1}, r_1 = 6.90 mM^{-1}s^{-1}$) and($r_2 = 9.20 mM^{-1}s^{-1}, r_1 = 4.30 mM^{-1}s^{-1}$) for nanoparticle sizes of 18 and 6 nm, respectively. These results confirm that the synthesized nanoparticles have both high $r_1$ and $r_2$ relaxivities and thus the capacity for positive or negative contrast enhancement. This effect increaseswith the nanoparticle size. We also developed a new recognition motif of a saccharide type (mannose coating) for targeting biological models (plants) at the tissue and cellular levels in order to track the flow of the water and saccharide (which are the main drivers of plant growth) in NMR imaging. Moreover, we demonstrated that this saccharide motif provides good biocompatibility and biodistribution in a physiological medium