Absolute Mag™ Amine Iron Oxide Nanoparticles, which are coated with amphiphilic polymer and dextran, are water soluble iron oxide nanocrystals. The functional group on surface is amine. Their zeta potential is from 0 mV to +10 mV. Their organic layers contain a monolayer of oleic acid, a monolayer of amphiphilic polymer, and a monolayer of dextran, whose thickness is about 6 nm. The hydrodynamic size of the nanocrystals is about 12-14 nm larger than their inorganic core size measured by the TEM. Absolute Mag™ Amine Iron Oxide Nanoparticles can be conjugated to carboxylic acid or amine containing molecules with low non-specific binding.