Zinc ferrite nanoparticles as MRI contrast agentsw

Magnetic resonance imaging (MRI) is a powerful clinical imaging technique for the non-invasive diagnosis and posttherapy assessment of a variety of diseases. MRI contrast can be enhanced by the use of positive or negative contrast agents resulting in brighter (T1-weighted) or darker (T2-weighted) images, respectively. Superparamagnetic iron oxide (SPIO) nanoparticles are T2 contrast agents that are widely used in molecular and cellular imaging applications. While most of the work in this area has been focused on acquiring biological specificity of SPIO by surface modifications, it still remains an open challenge to improve the magnetic properties of SPIO which would, in turn, lead to higher imaging sensitivity. Recently, a series of spinel-structured ferrites, MFe2O4 (M = Mn, Fe, Co, Ni), were reported as novel MRI contrast agents. In the spinel structure of general formula AB2O4 there are twice as many octahedral (B) sites as tetrahedral (A) sites. If M occupies only the A sites, the spinel is normal; if it occupies only the B sites, the spinel is inverse. In the above series, MnFe2O4 has a mixed spinel structure (i.e., Mn 2+