Solution to the bioheat equation for hyperthermia with La(1-x)Ag(y)MnO(3-delta) nanoparticles: the effect of temperature autostabilization.

This work aimed to analyze the possibility and performance of the temperature controlled hyperthermia based on AC heating of magnetic nanoparticles with low Curie temperature. Temperature dependence of dynamic magnetic susceptibility has been studied experimentally on fine powders of La(0.8)Ag(0.15)MnO(2.95) in the frequency range of 0.5-2.0 MHz. Critical drop of the AC magnetic losses was found in the vicinity of the Curie point, T(C) = 42 degrees C. The obtained data was used in the numerical analysis of the bioheat equations under typical conditions of the hyperthermia treatment. The mathematical model includes a spherical tumor containing magnetic particles and surrounded by concentric healthy tissue, with account made for the blood perfusion. The calculations performed for various AC power, tumor sizes and doping geometries predict effective autostabilization of the temperature at T congruent with T(C) inside the tumor and steep temperature profile at the interface with the healthy tissue.

Ag-doped manganite nanoparticles: new materials for temperature-controlled medical hyperthermia.

The purpose of this study was to introduce newly synthesized nanomaterials as an alternative to superparamagnetic ironoxide based particles (SPIO) and thus to launch a new platform for highly controllable hyperthermia cancer therapy and imaging. The new material that forms the basis for this article is lanthanum manganite particles with silver ions inserted into the perovskite lattice: La(1-x)Ag(x)MnO(3+delta). Adjusting the silver doping level, it is possible to control the Curie temperature (T(c)) in the hyperthermia range of interest (41-44 degrees C). A new class of nanoparticles based on silver-doped manganites La(1-x)Ag(x)MnO(3+delta) is suggested. New nanoparticles are stable, and their properties were not affected by the typical ambient conditions in the living tissue. It is possible to monitor the particle uptake and retention by MRI. When these particles are placed into an alternating magnetic field, their temperature increases to the definite value near T(c) and then remains constant if the magnetic field is maintained. During the hyperthermia procedure, the temperature can be restricted, thereby preventing the necrosis of normal tissue. A new class of nanoparticles based on silver-doped manganites La(1-x)Ag(x)MnO(3+delta) was suggested. Ag-doped perovskite manganites particles clearly demonstrated the effect of adjustable Curie temperature necessary for highly controllable cellular hyperthermia. The magnetic relaxation properties of the particles are comparable with that of SPIO, and so we were able to monitor the particle movement and retention by MRI. Thus, the new material combines the MRI contrast enhancement capability with targeted hyperthermia treatment.

NMR and spin relaxation in systems with magnetic nanoparticles: effects of size and molecular motion.

To better understand the specifics of nuclear magnetic resonance and spin relaxation in systems with magnetic nanoparticles and test the limits of the outer sphere model for the diffusion-related relaxation, iron oxide nanoparticle suspensions are studied in dependence on the particle concentration and size (5-40 nm). The model is modified to account for aggregation of the particles into clusters with an enlarged effective radius. For liquid suspensions containing small particles or clusters, both the longitudinal and transverse spin relaxation rates, T(1)(-1) and T(2)(-1), correspond well to the theory, which predicts passing of T(1)(-1) through a maximum and monotonic increase in T(2)(-1) with increasing particle size. For the largest particle sizes, as well as in the case of strong aggregation, the relaxation rates are significantly lower than theoretical predictions. An abrupt change in both the relaxation rates is observed in a narrow temperature range around the melting point of paraffin wax doped with magnetic nanoparticles. The applicability of fast-motion and fast-diffusion approximations is discussed for large effective sizes and limiting molecular motion cases.

Magnetic resonance in nanoparticles: between ferro- and paramagnetism.

Magnetic nanoparticles of γ-Fe(2)O(3) coated with organic molecules and suspended in liquid and solid matrices, as well as non-diluted magnetic fluid, have been studied by electron magnetic resonance (EMR) at 77-380 K. Slightly asymmetric spectra observed at room temperature become much broader and symmetric, and shift to lower fields upon cooling. An additional narrow spectral component (with a line-width of 30 G) is found in diluted samples; its magnitude obeys the Arrhenius law with an activation temperature of about 850 K. The longitudinal spin-relaxation time, T(1)≈10 ns, is determined by a specially developed modulation method. The angular dependence of the EMR signal position in field-freezing samples points to substantial alignment, suggesting the formation of dipolar-coupled aggregates. The shift and broadening of the spectrum upon cooling are assigned to the effect of the surface-related anisotropy. To describe the overall spectral shape, the 'quantization' model is used which includes summation of resonance transitions over the whole energy spectrum of a nanoparticle considered as a giant exchange cluster. This approach, supplemented with some phenomenological assumptions, provides satisfactory agreement with the experimental data.

NMR and spin relaxation in systems with magnetic nanoparticles.

The ¹H NMR spectra and spin dynamics of the host systems have been studied in liquid and solid suspensions of γ-Fe2O3 nanoparticles. Significant broadening of ¹H NMR spectra and growing relaxation rates were observed with increased concentration of nanoparticles in the liquid systems, with the relation T1/T2 depending on the particular host. Solid systems demonstrate inhomogeneous broadening of the spectra and practically no dependence of T1 upon the nanoparticle concentration. We explain the experimental results taking into account the predomination of self-diffusion as a source of the relaxation in liquid suspensions, and estimate effective parameters of relaxation in the systems under study.

Mechanism of oxygen response in carbon-based sensors.

The mechanism of oxygen response in several newly synthesized oxygen-sensitive chars was studied with the use of EPR spectroscopy. The results suggest that the compounds contain two basic types of paramagnetic centers (PC). The change in oxygen concentration leads to a mutual and reversible transformation of PCs in chars, which is reflected in EPR parameters. The adsorbed molecular oxygen progressively disturbs the wave functions of the PCs and so breaks the Heisenberg exchange between them. At high oxygen concentration, the 2D dipole-dipole interaction between PCs at the surface comes into play and determines the EPR lineshape. A suggested model quantitatively describes the evolution of the basic EPR parameters of each PC as a function of oxygen concentration.