Absolute Mag™ Lipid Coated Iron Oxide Nanoparticles, 20 nm (# WNM-X087) which are lipid coated and have no reactive groups on their surface, are water soluble iron oxide nanoparticles. Their organic layers have about 1-2 nm thickness and zeta potential ranges from -10 mV to -20 mV. Their hydrodynamic size using a Zeta Trac (DLS) is about 3-8 nm larger than the inorganic core size measured with TEM. The coating physiological lipid makes excellent compatibility for in vivo studies. Absolute Mag™ Lipid Coated Iron Oxide Nanoparticles are autoclavable, stable and resistant in general biocompatible buffers like borate, Tris, HEPES, PBS and MES buffers, as well as in cell culture medium.