Immobilization of magnetic iron oxide nanoparticles on laponite discs - an easy way to biocompatible ferrofluids and ferrogels

Magnetic nanocomposites containing iron oxide (maghemite - gamma-Fe2O3) nanoparticles, embedded in a synthetic clay matrix (laponite) were prepared by a new one step chemical route and characterized by TEM, XRD, magnetization measurements, Mossbauer spectroscopy, DLS, and MRI measurements. The synthesis procedure leads to non-stoichiometric gamma-Fe2O3 with a controllable content in the nanocomposite. Magnetic nanoparticles incorporated in the diamagnetic clay matrix exhibit a mean diameter of 13 nm and superparamagnetic behaviour with a high saturation magnetization achievable at low applied magnetic fields. The in-field Mossbauer spectra and ZFC/FC magnetization curves reveal a perfect ferrimagnetic ordering within nanoparticles with negligible spin frustration and interparticle interactions due to the incorporation of maghemite nanoparticles into the nanocrystalline laponite matrix, thus, significantly avoiding their clustering and agglomeration. Magnetic iron oxide nanoparticles embedded in the laponite matrix exhibit strong T-2-weighted MRI contrast. The gamma-Fe2O3/laponite nanocomposite particles have a 200 nm hydrodynamic diameter and form very stable hydrosols and/or hydrogels depending on their concentration in water.