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The MnxNi1-xFe2O4 nanoparticles with Mn contents of x=0.3, 0.6, and 0.8 were synthesized by using hydrothermal technique. The surfaces of the particles were coated with the TEG (Triethylene glycol) during the synthesis of the particles. The characterization of the particles were performed by using various analytic tools to see if the particles are suitable for biomedical applications such as MRI contrast agents and heat generators in magnetic hyperthermia.
The shape and size distribution of the particles were investigated by using an electron microscope. The particles were spherical with average diameters of 6 and 12.48 nm, respectively, for the particles with Mn contents of x=0.3 and 0.6. On the other hand, the particles were cubic with an average side of 52.8 nm for the particles with Mn content of x=0.8. The coating status of the TEG on the surfaces of the particles were checked by using Fourier transform infrared (FTIR) spectroscopy. The absorption bands in the FTIR spectra showed that the specific elements in the nanoparticles and TEG were bonded together indicating that the TEG was well coated on the surfaces of the particles. The particles showed the inverse spinel crystalline structure in the XRD patterns, which is typical characteristics of the ferrites. The magnetic hysteresis curves at room temperature revealed that the particles were superparamagnetic with negligible coercive forces. This superparamagnetic behavior is essential for the biomedical applications of the magnetic nanoparticles. The aqueous solutions of the particles with various particle concentrations were prepared to test the contrast and heating effects of the particles. The particle concentrations in the aqueous solutions were determined by using inductively coupled plasma spectroscopy. The T1 and T2 relaxation times of the hydrogen protons in the aqueous solution of the particles were determined by using a 4.7 T magnetic resonance (MRI) scanner. The T1 relaxivities were determined to be 0.32, 1.44 and 0.06 mM-1s-1, respectively, for the x=0.3, 0.6, and 0.8 samples. On the other hand, the T2 relaxivities were 45.3, 128.7, and 5.94 mM-1s-1, respectively, for the x=0.3, 0.6, and 0.8 samples. These data showed that the spherical particles are suitable for the T2 contrast agents in MRI. However, the relaxivities of the cube-shaped particles were too small compared with those of the spherical particles, and thus these particles are not suitable for the contrast agents. Consequently, we can conclude from these data that the spherical (x=0.3 and 0.6) particles can be applicable as T2 contrast agent in MRI, but the cubic particles did not show high T2 relaxivity suitable for the T2 contrast agent.
The heating effects of the particles were tested by using an induction heating system. The temperature of the aqueous solution of the particle in the external alternating magnetic field (constant field intensity of 4.4 kA/m at 260 kHz) was raised due to the heat generated by particles. The optimum particle concentrations in the solution to raise the saturation temperature of the aqueous solution up to 42°C for magnetic hyperthermia were determined to be 15, 10, 6.5 mg/mL, respectively, for the x=0.3, 0.6, and 0.8 samples. The corresponding SARs (specific absorption rate) were 47, 35, and 40 W/g, respectively, for the x=0.3, 0.6, and 0.8 samples. The field intensity dependence of the SAR was also tested with an aqueous solution of a fixed particle concentration. The dependence of the SAR on the square of the field intensity was confirmed. We can conclude in this study that both spherical (x=0.3 and 0.6) and cubic (x=0.8) particles are suitable for applying them as heat generators in magnetic hyperthermia.
The spherical- and cube-shaped Mn0.5Ni0.5Fe2O4 nanoparticles were synthesized to investigate the shape dependence of the physical properties. The surfaces of the particles were encapsulated with the TEG during the synthesis of the particles. The average diameter of the spherical particles was 5.2 nm while the average side of the cubic particles was 68.1 nm indicating that the spherical particles are much smaller than the cubic ones.
The T1 relaxivities were determined to be 0.89 and 0.32 mM-1s-1, respectively, for the spherical and cubic particles. On the other hand, the T2 relaxivities were 53 and 14.59 mM-1s-1, respectively, for the spherical and cubic particles. The particle sizes of the cube-shaped particles were much larger than those of the spherical ones. However, the values of the relaxivities for the cubic particles were less than one third those for the spherical ones. Nevertheless, the T2 relaxivity for the cubic particles is not that small for applying them as contrast agents.
The optimum particle concentration in the aqueous solution for the spherical particles as heat generators in magnetic hyperthermia were lower than 4 mg/mL. On the other hand, the optimum particle concentration for the cubic particles as heat generators in magnetic hyperthermia were 2 mg/mL. The SARs for these optimum particle concentration were 80 and 40 W/g, respectively, for the spherical and cubic particles. Thus, we can conclude that both spherical and cubic particles are suitable for applying them as heat generators in hyperthermia.
Thesis Advisor: Prof. Ilsu Rhee