A highly sensitive magnetite nanoparticle as a simple and rapid stem cell labelling agent for MRI tracking

A superparamagnetic iron oxide nanoparticle (SPION) was coupled to 2-aminoethyl-trimethyl ammonium (TMA) in a 2-step ligand exchange reaction to produce TMA–SPION. This particle, which has a strong positive charge, was investigated as the basis for a simple and efficient method for labelling human mesenchymal stem cells (hMSCs) for noninvasive monitoring by magnetic resonance imaging (MRI). TMA–SPION has a ζ potential of +40 mV and a hydrodynamic size of 101 nm. In addition to its long-term stability in an aqueous solution, TMA–SPION has a low cytotoxicity and favourable magnetic properties as a T2 contrast agent due to its high relaxivity. The T2 relaxivity of TMA–SPION is 4.4 times greater than the commercially available Feridex® I.V. magnetic resonance agent. Despite a short labelling time of 4 h, hMSCs are efficiently labelled with TMA–SPION without the need for a transfection agent. An in vivo MRI study of a brain infarction model confirmed the utility of TMA–SPION as an MRI tracking marker of administered hMSCs.