  Super-paramagnetic nanoparticles (NPs) have been widely explored as magnetic
resonance imaging (MRI) contrast agents because of a combination of favorable
magnetic properties, biocompability and ease of fabrication. MRI using
traditional T1- or T2-weighted single mode contrast-enhanced techniques may
yield inaccurate imaging results. In the present work, a T1/T2 dual mode
contrast agent based on the super-paramagnetic zinc-manganese ferrite
(Zn$_{0.3}$Mn$_x$Fe$_{2.7-x}$O$_4$, x= 0, 0.25, 0.75 and 1) NPs with small core
size and a hydrophilic PEG surface coating is reported. The TEM, TGA and FTIR
results confirmed the formation of a uniform coating on the NPs surface. The
MRI analysis revealed that the Zn$_{0.3}$Mn$_{0.5}$Fe$_{2.2}$O$_4$ NPs had the
maximum image contrast compared to other zinc-manganese ferrite samples. Cell
viability evaluations revealed that the coated and uncoated particles did not
inhibit cell growth pattern. The present PEG-coated
Zn$_{0.3}$Mn$_{0.5}$Fe$_{2.2}$O$_4$ NPs can be utilized as a suitable
T1/T2-weighted MRI contrast agent for better diagnostic of abnormalities in the
organs or tissues.
