Linear and nonlinear magneto-optics of ferritin

Method for Determining Average Iron Content of Ferritin by Measuring its Optical Dispersion

We report a method where the refractive index increments of an iron storage protein, ferritin, and apoferritin (ferritin minus iron) were measured over the wavelength range of 450-678 nm to determine the average iron content of the protein. The protein used in this study had ∼3375 iron atoms per molecule. The measurement of optical dispersion over the broad wavelength range was enabled by the use of mesoporous leaky waveguides (LWs) made of chitosan. We present a facile approach for fabricating mesoporous chitosan waveguides for improving the measurement sensitivity of macromolecules such as ferritin. Mesoporous materials allow macromolecules to diffuse into the waveguide, maximizing their interaction with the optical mode and thus increasing sensitivity by a factor of ∼9 in comparison to nonporous waveguides. The sensitivity was further improved and selectivity toward ferritin was achieved by the incorporation of antibodies in the waveguide. The method presented in this work is a significant advance over the state of the art method, the enzyme linked immunosorbent assay (ELISA) used in clinics, because it allows determining the average content of ferritin in a single step. The average iron content of ferritin is an important marker for conditions such as injury, inflammation, and infection. Thus, the approach presented here of measuring optical dispersion to determine the average iron content of ferritin has a significant potential to improve the point of care analysis of the protein for disease diagnosis and screening.

Morphology and Magnetic Structure of the Ferritin Core during Iron Loading and Release by Magnetooptical and NMR Methods

Ferritins are proteins, which serve as a storage and transportation capsule for iron inside living organisms. Continuously charging the proteins with iron and releasing it from the ferritin is necessary to assure proper management of these important ions within the organism. On the other hand, synthetic ferritins have great potential for biomedical and technological applications. In this work, the behavior of ferritin during the processes of iron loading and release was examined using multiplicity of the experimental technique. The quality of the protein's shell was monitored using circular dichroism, whereas the average size and its distribution were estimated from dynamic light scattering and transmission electron microscopy images, respectively. Because of the magnetic behavior of the iron mineral, a number of magnetooptical methods were used to gain information on the iron core of the ferritin. Faraday rotation and magnetic linear birefringence studies provide evidence that the iron loading and the iron-release processes are not symmetrical. The spatial organization of the mineral within the protein's core changes depending on whether the iron was incorporated into or removed from the ferritin's shell. Magnetic optical rotatory dispersion spectra exclude the contribution of the Fe(II)-composed mineral, whereas joined magnetooptical and nuclear magnetic resonance results indicate that no mineral with high magnetization appear at any stage of the loading/release process. These findings suggest that the iron core of loaded/released ferritin consists of single-phase, that is, ferrihydrite. The presented results demonstrate the usefulness of emerging magnetooptical methods in biomedical research and applications.

Magnetic mapping of iron in rodent spleen

Evaluation of iron distribution and density in biological tissues is important to understand the pathogenesis of a variety of diseases and the fate of exogenously administered iron-based carriers and contrast agents. Iron distribution in tissues is typically characterized via histochemical (Perl's) stains or immunohistochemistry for ferritin, the major iron storage protein. A more accurate mapping of iron can be achieved via ultrastructural transmission electron microscopy (TEM) based techniques, which involve stringent sample preparation conditions. In this study, we elucidate the capability of magnetic force microscopy (MFM) as a label-free technique to map iron at the nanoscale level in rodent spleen tissue. We complemented and compared our MFM results with those obtained using Perl's staining and TEM. Our results show how MFM mapping corresponded to sizes of iron-rich lysosomes at a resolution comparable to that of TEM. In addition MFM is compatible with tissue sections commonly prepared for routine histology.

Magnetic properties of ferritin and akaganeite nanoparticles in aqueous suspension

We have studied the magnetically induced optical birefringence Δn of horse spleen ferritin (HSF) and aqueous suspensions of several different-sized iron oxyhydroxide nanoparticles coated with different polysaccharides mimicking ferritin. The structure and dimensions of the akaganeite mineral core were characterized by XRD and TEM, respectively. The stability of the suspensions in the measurement temperature range from 278 to 358 K was confirmed by UV-Vis absorption spectroscopy. The values of optical polarizability anisotropy Δα, magnetic susceptibility anisotropy Δχ, and permanent magnetic dipole moment μm of the akaganeite nanoparticles have been estimated on the basis of the temperature dependence of the Cotton-Mouton (C-M) constant. The magnetic birefringence of Fe-sucrose has been described tentatively by different types of Langevin function allowing another estimation of Δχ and μm. The obtained permanent magnetic dipole moment μm of the studied akaganeite nanoparticles proves small and comparable to that of HSF. The value of μm is found to increase with decreasing nanoparticle diameter. Observed in a range spanning more than five orders of magnitude, the linear relation between the C-M constant and the iron concentration provides a basis for possible analytical application of the C-M effect in biomedicine. The established relation between the C-M constant and the nanoparticle diameter confirms that the dominant contribution to the measured magnetic birefringence comes from the magnetic susceptibility anisotropy Δχ. A comparison of the C-M constants of the studied akaganeite nanoparticles with the data obtained for HSF provides evidence that the ferritin core behaves as a non-Euclidian solid.