Aqueous Dispersion of Manganese–Zinc Ferrite Nanoparticles Protected by PEG as a T2 MRI Temperature Contrast Agent

Abstract

Mixed manganese–zinc ferrite nanoparticles coated with PEG were studied for their potential usefulness in MRI thermometry as temperature-sensitive contrast agents. Particles in the form of an 8.5 nm core coated with a 3.5 nm layer of PEG were fabricated using a newly developed, one-step method. The composition of Mn0.48Zn0.46Fe2.06O4 was found to have a strong thermal dependence of magnetization in the temperature range between 5 and 50 °C. Nanoparticles suspended in an agar gel mimicking animal tissue and showing non-significant impact on cell viability in the biological test were studied with NMR and MRI over the same temperature range. For the concentration of 0.017 mg/mL of Fe, the spin–spin relaxation time T2 increased from 3.1 to 8.3 ms, while longitudinal relaxation time T1 shows a moderate decrease from 149.0 to 125.1 ms. A temperature map of the phantom exposed to the radial temperature gradient obtained by heating it with an 808 nm laser was calculated from T2 weighted spin-echo differential MR images. Analysis of temperature maps yields thermal/spatial resolution of 3.2 °C at the distance of 2.9 mm. The experimental relaxation rate R2 data of water protons were compared with those obtained from calculations using a theoretical model incorporating the motion averaging regime.

Progress in ultrasmall ferrite nanoparticles enhanced T1 magnetic resonance angiography

“…For instance, the amphiphilic ionic molecule dopamine sulfonate forms a dense water shell on the surface of the nanoparticles by hydrogen bonding between its positive and negative charge groups, preventing nonspecific adsorption of proteins. 84 Various hydrophilic and biosafe polymers and small molecules, including dextran, 85,86 polyethylene glycol (PEG), 61,87 dopamine, 88 and citric acid, 89 have also been used to modify the surface of UFNPs.…”