Low-frequency low-field magnetic susceptibility of ferritin and hemosiderin

Non-Stokesian dynamics of magnetic helical nanoswimmers under confinement

Electromagnetically propelled helical nanoswimmers offer great potential for nanorobotic applications. Here, the effect of confinement on their propulsion is characterized using lattice-Boltzmann simulations. Two principal mechanisms give rise to their forward motion under confinement: (i) pure swimming and (ii) the thrust created by the differential pressure due to confinement. Under strong confinement, they face greater rotational drag but display a faster propulsion for fixed driving frequency in agreement with experimental findings. This is due to the increased differential pressure created by the boundary walls when they are sufficiently close to each other and the particle. We have proposed two analytical relations (i) for predicting the swimming speed of an unconfined particle as a function of its angular speed and geometrical properties, and (ii) an empirical expression to accurately predict the propulsion speed of a confined swimmer as a function of the degree of confinement and its unconfined swimming speed. At low driving frequencies and degrees of confinement, the systems retain the expected linear behavior consistent with the predictions of the Stokes equation. However, as the driving frequency and/or the degree of confinement increase, their impact on propulsion leads to increasing deviations from the Stokesian regime and emergence of nonlinear behavior.

Capillary Force-Driven Quantitative Plasma Separation Method for Application of Whole Blood Detection Microfluidic Chip

Separating plasma or serum from blood is essential for precise testing. However, extracting precise plasma quantities outside the laboratory poses challenges. A recent study has introduced a capillary force-driven membrane filtration technique to accurately separate small plasma volumes. This method efficiently isolates 100-200 μL of pure human whole blood with a 48% hematocrit, resulting in 5-30 μL of plasma with less than a 10% margin of error. The entire process is completed within 20 min, offering a simple and cost-effective approach to blood separation. This study has successfully addressed the bottleneck in self-service POCT, ensuring testing accuracy. This innovative method shows promise for clinical diagnostics and point-of-care testing.

A Review of the Current State of Magnetic Force Microscopy to Unravel the Magnetic Properties of Nanomaterials Applied in Biological Systems and Future Directions for Quantum Technologies

Magnetism plays a pivotal role in many biological systems. However, the intensity of the magnetic forces exerted between magnetic bodies is usually low, which demands the development of ultra-sensitivity tools for proper sensing. In this framework, magnetic force microscopy (MFM) offers excellent lateral resolution and the possibility of conducting single-molecule studies like other single-probe microscopy (SPM) techniques. This comprehensive review attempts to describe the paramount importance of magnetic forces for biological applications by highlighting MFM's main advantages but also intrinsic limitations. While the working principles are described in depth, the article also focuses on novel micro- and nanofabrication procedures for MFM tips, which enhance the magnetic response signal of tested biomaterials compared to commercial nanoprobes. This work also depicts some relevant examples where MFM can quantitatively assess the magnetic performance of nanomaterials involved in biological systems, including magnetotactic bacteria, cryptochrome flavoproteins, and magnetic nanoparticles that can interact with animal tissues. Additionally, the most promising perspectives in this field are highlighted to make the reader aware of upcoming challenges when aiming toward quantum technologies.

Effects of fixatives on histomagnetic evaluation of iron in rodent spleen

Characterizing the iron distribution in tissue sections is important for several pathologies. Iron content in excised tissue is typically analyzed via histochemical stains, which are dependent on sample preparation and staining protocols. In our recent studies, we examined how magnetic properties of iron can also be exploited to characterize iron distribution in tissue sections in a label free manner. To enable a histomagnetic characterization of iron in a wide variety of available tissues, it is important to extend it to samples routinely prepared for histochemical staining, which often involve use of chemical fixatives. In this study, we took a systematic approach to determine differences between unfixed and formalin-fixed murine spleen tissues in histomagnetic characterization of iron. Superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM) were used for macro- and micro-scale histomagnetic characterization. Perl's stain was used for histochemical characterization of ferric (Fe³⁺) iron on adjacent sections as that used for MFM analysis. While histochemical analysis revealed a substantial difference in the dispersion of the stain between fixed versus unfixed samples, histomagnetic characterization was not dependent on chemical fixation of tissue. The results from this study reveal that histomagnetic characterization of iron is free from staining artifacts which can be present in histochemical analysis.

Ultrahigh throughput beehive-like device for blood plasma separation

We report here a low-cost, rapid-prototyping, and beehive-like multilayer polymer microfluidic device for ultrahigh-throughput blood plasma separation. To understand the device physics and optimize the device structure, the effect of cross-sectional dimension and operational parameter on particle focusing behavior was explored using a single spiral microchannel device. Then, the blood plasma separation performance of the determined channel structure was validated using the blood samples with different hematocrits (HCTs). It was found that a high separation efficiency of 99% could be achieved using the blood sample with an HCT of 0.5% at a high throughput of 1 mL/min. Finally, a multilayer microfluidic device with a novel beehive-like multiplexing channel arrangement was developed for ultrahigh-throughput blood plasma separation. The prototype device could be fabricated within ∼1 hour utilizing the laser cutting and thermal lamination methods. The total processing throughput could reach up to 72 mL/min for 0.5% HCT sample with a plasma separation ratio close to 90%. Our device may hold potentials for the ultrahigh-throughput separation of blood plasma from large volume blood samples for downstream disease diagnosis.

Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics

The palette of tools for perturbation of neural activity is continually expanding. On the forefront of this expansion is magnetogenetics, where ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Initial reports on magnetogenetics have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. The criticism leveled against magnetogenetics as being physically implausible is based on the specific assumptions about the magnetic spin configurations of iron in ferritin. I consider here a wider range of possible spin configurations of iron in ferritin and the consequences these might have in magnetogenetics. I propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation that may clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.

Cerebral Micro-Bleeding Detection Based on Densely Connected Neural Network

Cerebral micro-bleedings (CMBs) are small chronic brain hemorrhages that have many side effects. For example, CMBs can result in long-term disability, neurologic dysfunction, cognitive impairment and side effects from other medications and treatment. Therefore, it is important and essential to detect CMBs timely and in an early stage for prompt treatment. In this research, because of the limited labeled samples, it is hard to train a classifier to achieve high accuracy. Therefore, we proposed employing Densely connected neural network (DenseNet) as the basic algorithm for transfer learning to detect CMBs. To generate the subsamples for training and test, we used a sliding window to cover the whole original images from left to right and from top to bottom. Based on the central pixel of the subsamples, we could decide the target value. Considering the data imbalance, the cost matrix was also employed. Then, based on the new model, we tested the classification accuracy, and it achieved 97.71%, which provided better performance than the state of art methods.

Elevated Brain Iron in Cocaine Use Disorder as Indexed by Magnetic Field Correlation Imaging

BACKGROUND

Iron homeostasis is a critical biological process that may be disrupted in cocaine use disorder (CUD). In the brain, iron is required for neural processes involved in addiction and can be lethal to cells if unbound, especially in excess. Moreover, recent studies have implicated elevated brain iron in conditions of prolonged psychostimulant exposure. Thus, the purpose of this study was to examine iron in basal ganglia reward regions of individuals with CUD using an advanced imaging method called magnetic field correlation (MFC) imaging.

METHODS

MFC imaging was acquired in 19 non-treatment-seeking individuals with CUD and 19 healthy control individuals (both male and female). Region-of-interest analyses for MFC group differences and within-group correlations with age and years of cocaine use were conducted in the globus pallidus internal segment (GPi), globus pallidus external segment, putamen, caudate nucleus, thalamus, and red nucleus.

RESULTS

Individuals with CUD had significantly elevated MFC compared with control individuals within the GPi. In control individuals, MFC significantly increased with age in the GPi, globus pallidus external segment, putamen, and caudate nucleus. Conversely, there were no significant MFC within-group correlations in the CUD group.

CONCLUSIONS

Individuals with CUD have excess iron in the GPi, as indexed by MFC, and lack the age-related gradual iron deposition seen in normal aging. Because the globus pallidus is critical for the transition of goal-directed behavior to compulsive behavior, significantly elevated iron in the GPi may contribute to the persistence of CUD. These findings implicate dysregulation of brain iron homeostasis in CUD and support pursuing this new line of research.

Proposal to use superparamagnetic nanoparticles to test the role of cryptochrome in magnetoreception

Evidence is accumulating to support the hypothesis that some animals use light-induced radical pairs to detect the direction of the Earth's magnetic field. Cryptochrome proteins seem to be involved in the sensory pathway but it is not yet clear if they are the magnetic sensors: they could, instead, play a non-magnetic role as signal transducers downstream of the primary sensor. Here we propose an experiment with the potential to distinguish these functions. The principle is to use superparamagnetic nanoparticles to disable any magnetic sensing role by enhancing the electron spin relaxation of the radicals so as to destroy their spin correlation. We use spin dynamics simulations to show that magnetoferritin, a synthetic, protein-based nanoparticle, has the required properties. If cryptochrome is the primary sensor, then it should be inactivated by a magnetoferritin particle placed 12-16 nm away. This would prevent a bird from using its magnetic compass in behavioural tests and abolish magnetically sensitive neuronal firing in the retina. The key advantage of such an experiment is that any signal transduction role should be completely unaffected by the tiny magnetic interactions (≪kBT) required to enhance the spin relaxation of the radical pair.

Possible role of iron containing proteins in physiological responses of soybean to static magnetic field

Iron is a component of many proteins that have crucial roles in plant growth and development, such as ferritin and catalase. Iron also, as a ferromagnetic element, is assumed to be influenced by a static magnetic field (SMF). In the present study, we examined the relationship between ferrous content and gene expression and activity of ferritin and catalase in soybean plants under the influence of 0, 20, and 30 mT SMF for 5 day, 5 h each. Exposure to 20 mT decreased gene expression of Fe transporter, ferrous and H2O2 contents and gene expression, content and activity of ferritin and catalase. Opposite responses were observed under 30 mT treatments. The results suggest that SMF triggered a signaling pathway that is mediated by iron. The structure and activity of purified ferritin and apoferritin from horse spleen, and catalase from bovine liver proteins under SMF were evaluated as well. Secondary structure of proteins were not influenced by SMF (evidenced by far-UV circular dichroism), whereas their tertiary structure, size, and activity were altered (shown by fluorescence spectroscopy and dynamic light-scattering). From these results, it is likely that the number of iron atoms is involved in the nature of influence of SMF on protein structure.

Iron imaging reveals tumor and metastasis macrophage hemosiderin deposits in breast cancer

Iron-deposition is a metabolic biomarker of macrophages in both normal and pathological situations, but the presence of iron in tumor and metastasis-associated macrophages is not known. Here we mapped and quantified hemosiderin-laden macrophage (HLM) deposits in murine models of metastatic breast cancer using iron and macrophage histology, and in vivo MRI. Iron MRI detected high-iron pixel clusters in mammary tumors, lung metastasis, and brain metastasis as well as liver and spleen tissue known to contain the HLMs. Iron histology showed these regions to contain clustered macrophages identified by their common iron status and tissue-intrinsic association with other phenotypic macrophage markers. The in vivo MRI and ex vivo histological images were further processed to determine the frequencies and sizes of the iron deposits, and measure the number of HLMs in each deposit to estimate the in vivo MRI sensitivity for these cells. Hemosiderin accumulation is a macrophage biomarker and intrinsic contrast source for cellular MRI associated with the innate function of macrophages in iron metabolism systemically, and in metastatic cancer.

Sensitive and non-invasive assessment of hepatocellular iron using a novel room-temperature susceptometer

BACKGROUND & AIMS

Liver iron accumulates in various chronic liver diseases where it is an independent factor for survival and carcinogenesis. We tested a novel room-temperature susceptometer (RTS) to non-invasively assess liver iron concentration (LIC).

METHODS

Two hundred and sixty-four patients with or without signs of iron overload or liver disease were prospectively enrolled. Thirty-five patients underwent liver biopsy with semiquantitative iron determination (Prussian Blue staining), atomic absorption spectroscopy (AAS, n=33), or magnetic resonance imaging (MRI, n=15).

RESULTS

In vitro studies demonstrated a highly linear (r²=0.998) association between RTS-signal and iron concentration, with a detection limit of 0.3mM. Using an optimized algorithm, accounting for the skin-to-liver capsule distance, valid measurements could be obtained in 84% of cases. LIC-RTS showed a significant correlation with LIC-AAS (r=0.74, p<0.001), LIC-MRI (r=0.64, p<0.001) and hepatocellular iron (r=0.58, p<0.01), but not with macrophage iron (r=0.32, p=0.30). Normal LIC-RTS was 1.4mg/g dry weight. Besides hereditary and transfusional iron overload, LIC-RTS was also significantly elevated in patients with alcoholic liver disease. The areas under the receiver operating characteristic curve (AUROC) for grade 1, 2 and 3 hepatocellular iron overload were 0.72, 0.89 and 0.97, respectively, with cut-off values of 2.0, 4.0 and 5.0mg/g dry weight. Notably, the positive and negative predictive values, sensitivity, specificity and accuracy of severe hepatic iron overload (HIO) (grade ≥2) detection, were equal to AAS and superior to all serum iron markers. Depletion of hepatic iron could be efficiently monitored upon phlebotomy.

CONCLUSIONS

RTS allows for the rapid and non-invasive measurement of LIC. In comparison to MRI, it could be a cost-effective bedside method for LIC screening. Lay summary: Novel room-temperature susceptometer (RTS) allows for the rapid, sensitive, and non-invasive measurement of liver iron concentration. In comparison to MRI, it could be a cost-effective bedside method for liver iron concentration screening.

Physiological origin of biogenic magnetic nanoparticles in health and disease: from bacteria to humans

The discovery of biogenic magnetic nanoparticles (BMNPs) in the human brain gives a strong impulse to study and understand their origin. Although knowledge of the subject is increasing continuously, much remains to be done for further development to help our society fight a number of pathologies related to BMNPs. This review provides an insight into the puzzle of the physiological origin of BMNPs in organisms of all three domains of life: prokaryotes, archaea, and eukaryotes, including humans. Predictions based on comparative genomic studies are presented along with experimental data obtained by physical methods. State-of-the-art understanding of the genetic control of biomineralization of BMNPs and their properties are discussed in detail. We present data on the differences in BMNP levels in health and disease (cancer, neurodegenerative disorders, and atherosclerosis), and discuss the existing hypotheses on the biological functions of BMNPs, with special attention paid to the role of the ferritin core and apoferritin.

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.

A USPIO doped gel phantom for R2* relaxometry

OBJECTIVE

This work describes a phantom containing regions of controlled R2* (1/T2*) values to provide a stable reference object for testing implementations of R2* relaxometry commonly used for liver and heart iron assessments.

MATERIALS AND METHODS

A carrageenan-strengthened gadolinium DTPA doped agarose gel was used to enclose nine gels additionally doped with ultra-small superparamagnetic iron oxide. R2* values were determined at 1.5 T using multi-echo GRE sequences and exponential regression of pixel values from a region of interest against echo time using non-linear regression algorithms. We measured R2*, R2 and R1 values and the inter-scan and inter-operator reproducibility.

RESULTS

The phantom reliably demonstrated R2* values in seven steps between 22.4 s^-1 (SE 1.98) and 441.9 s^-1 (SE 6.76), with an R2* relaxivity (r2*) of 792 (SE 5.6) mM^-1 s^-1. The doped gels displayed a concentration-dependent R2' component of R2* phantom, indicating superparamagnetic enhancement effects. We observed no significant change in relaxivity (r2*) over 12 months, and estimate a useful life of 3 years. Detailed descriptions of the production process and calculators are been provided as Online Resources.

CONCLUSION

The phantom provides a durable test object with controlled R2* relaxation behaviour, useful for a range of R2* relaxometry reference work.

Superparamagnetic [sic] nanofibers by electrospinning

Magnetically ultra-soft and anisotropic electrospun fibre mats.

Iron oxides in human spleen

Iron is an essential element for fundamental cell functions and a catalyst for chemical reactions. Three samples extracted from the human spleen were investigated by scanning (SEM) and transmission electron microscopy (TEM), Mössbauer spectrometry (MS), and SQUID magnetometry. The sample with diagnosis of hemosiderosis (H) differs from that referring to hereditary spherocytosis and the reference sample. SEM reveals iron-rich micrometer-sized aggregate of various structures-tiny fibrils in hereditary spherocytosis sample and no fibrils in hemochromatosis. Hematite and magnetite particles from 2 to 6 μm in TEM with diffraction in all samples were shown. The SQUID magnetometry shows different amount of diamagnetic, paramagnetic and ferrimagnetic structures in the tissues. The MS results indicate contribution of ferromagnetically split sextets for all investigated samples. Their occurrence indicates that at least part of the sample is magnetically ordered below the critical temperature. The iron accumulation process is different in hereditary spherocytosis and hemosiderosis. This fact may be the reason of different iron crystallization.

Splenic red pulp macrophages are intrinsically superparamagnetic and contaminate magnetic cell isolates

A main function of splenic red pulp macrophages is the degradation of damaged or aged erythrocytes. Here we show that these macrophages accumulate ferrimagnetic iron oxides that render them intrinsically superparamagnetic. Consequently, these cells routinely contaminate splenic cell isolates obtained with the use of MCS, a technique that has been widely used in immunological research for decades. These contaminations can profoundly alter experimental results. In mice deficient for the transcription factor SpiC, which lack red pulp macrophages, liver Kupffer cells take over the task of erythrocyte degradation and become superparamagnetic. We describe a simple additional magnetic separation step that avoids this problem and substantially improves purity of magnetic cell isolates from the spleen.

Distinguishing ferritin from apoferritin using magnetic force microscopy

Estimating the amount of iron-replete ferritin versus iron-deficient apoferritin proteins is important in biomedical and nanotechnology applications. This work introduces a simple and novel approach to quantify ferritin by using magnetic force microscopy (MFM). We demonstrate how high magnetic moment probes enhance the magnitude of MFM signal, thus enabling accurate quantitative estimation of ferritin content in ferritin/apoferritin mixtures in vitro. We envisage MFM could be adapted to accurately determine ferritin content in protein mixtures or in small aliquots of clinical samples.

Fat and iron quantification in the liver: past, present, and future

Liver fat, iron, and combined overload are common manifestations of diffuse liver disease and may cause lipotoxicity and iron toxicity via oxidative hepatocellular injury, leading to progressive fibrosis, cirrhosis, and eventually, liver failure. Intracellular fat and iron cause characteristic changes in the tissue magnetic properties in predictable dose-dependent manners. Using dedicated magnetic resonance pulse sequences and postprocessing algorithms, fat and iron can be objectively quantified on a continuous scale. In this article, we will describe the basic physical principles of magnetic resonance fat and iron quantification and review the imaging techniques of the "past, present, and future." Standardized radiological metrics of fat and iron are introduced for numerical reporting of overload severity, which can be used toward objective diagnosis, grading, and longitudinal disease monitoring. These noninvasive imaging techniques serve an alternative or complimentary role to invasive liver biopsy. Commercial solutions are increasingly available, and liver fat and iron quantitative imaging is now within reach for routine clinical use and may soon become standard of care.

Simultaneous field and R2 mapping to quantify liver iron content using autoregressive moving average modeling

PURPOSE

To investigate the use of a complex multigradient echo (mGRE) acquisition and an autoregressive moving average (ARMA) model for simultaneous susceptibility and R 2 measurements for the assessment of liver iron content (LIC) in patients with iron overload.

MATERIALS AND METHODS

Fifty magnetic resonance imaging (MRI) exams with magnitude and phase mGRE images were processed using the ARMA model, which provides fat-separated field maps, R 2 maps, and T(1) -W imaging. The LIC was calculated by measuring the susceptibility between the liver and the right transverse abdominal muscle from the field maps. The relationship between LIC derived from susceptibility measurements and LIC from R 2 measurements was determined using linear least-squares regression analysis.

RESULTS

LIC measured from R 2 is highly correlated to the LIC with the susceptibility method (mg/g dry = 8.99 ± 0.15 × [mg Fe/mL of wet liver] -2.38 ± 0.29, R(2) = 0.94). The field inhomogeneity in the liver is correlated with R 2 (R(2) = 0.85).

CONCLUSION

By using the ARMA model on complex mGRE images, both susceptibility and R 2-based LIC measurements can be made simultaneously. The susceptibility measurement can be used to help verify R 2 measurements in the assessment of iron overload.

Nanomagnetism reveals the intracellular clustering of iron oxide nanoparticles in the organism

There are very few methods to investigate how nanoparticles (NPs) are taken up and processed by cells in the organism in the short and long terms. We propose a nanomagnetism approach, in combination with electron microscopy, to document the magnetic outcome of iron oxide-based P904 NPs injected intravenously into mice. The NP superparamagnetic properties are shown to be modified by cell internalization, due to magnetic interactions between NPs sequestered within intracellular organelles. These modifications of magnetic behaviour are observed in vivo after NP uptake by resident macrophages in spleen and liver or by inflammatory macrophages in adipose tissue as well as in vitro in monocyte-derived macrophages. The dynamical magnetic response of cell-internalized NPs is theoretically and experimentally evidenced as a global signature of their local organization in the intracellular compartments. The clustering of NPs and their magnetism become dependent on the targeted organ, on the dose administrated and on the time elapsed since their injection. Nanomagnetism probes the intracellular clustering of iron-oxide NPs and sheds light on the impact of cellular metabolism on their magnetic responsivity.

Reduced transverse relaxation rate (RR2) for improved sensitivity in monitoring myocardial iron in thalassemia

PURPOSE

To evaluate the reduced transverse relaxation rate (RR2), a new relaxation index which has been shown recently to be primarily sensitive to intracellular ferritin iron, as a means of detecting short-term changes in myocardial storage iron produced by iron-chelating therapy in transfusion-dependent thalassemia patients.

MATERIALS AND METHODS

A single-breathhold multi-echo fast spin-echo sequence was implemented at 3 Tesla (T) to estimate RR2 by acquiring signal decays with interecho times of 5, 9 and 13 ms. Transfusion-dependent thalassemia patients (N = 8) were examined immediately before suspending iron-chelating therapy for 1 week (Day 0), after a 1-week suspension of chelation (Day 7), and after a 1-week resumption of chelation (Day 14).

RESULTS

The mean percent changes in RR2, R2, and R2* off chelation (between Day 0 and 7) were 11.9 ± 8.9%, 5.4 ± 7.7% and -4.4 ± 25.0%; and, after resuming chelation (between Day 7 and 14), -10.6 ± 13.9%, -8.9 ± 8.0% and -8.5 ± 24.3%, respectively. Significant differences in R2 and RR2 were observed between Day 0 and 7, and between Day 7 and 14, with the greatest proportional changes in RR2. No significant differences in R2* were found.

CONCLUSION

These initial results demonstrate that significant differences in RR2 are detectable after a single week of changes in iron-chelating therapy, likely as a result of superior sensitivity to soluble ferritin iron, which is in close equilibrium with the chelatable cytosolic iron pool. RR2 measurement may provide a new means of monitoring the short-term effectiveness of iron-chelating agents in patients with myocardial iron overload.

Long term in vivo biotransformation of iron oxide nanoparticles

The long term outcome of nanoparticles in the organism is one of the most important concerns raised by the development of nanotechnology and nanomedicine. Little is known on the way taken by cells to process and degrade nanoparticles over time. In this context, iron oxide superparamagnetic nanoparticles benefit from a privileged status, because they show a very good tolerance profile, allowing their clinical use for MRI diagnosis. It is generally assumed that the specialized metabolism which regulates iron in the organism can also handle iron oxide nanoparticles. However the biotransformation of iron oxide nanoparticles is still not elucidated. Here we propose a multiscale approach to study the fate of nanomagnets in the organism. Ferromagnetic resonance and SQUID magnetization measurements are used to quantify iron oxide nanoparticles and follow the evolution of their magnetic properties. A nanoscale structural analysis by electron microscopy complements the magnetic follow-up of nanoparticles injected to mice. We evidence the biotransformation of superparamagnetic maghemite nanoparticles into poorly-magnetic iron species probably stored into ferritin proteins over a period of three months. A putative mechanism is proposed for the biotransformation of iron-oxide nanoparticles.

Electromagnetic irradiation exposure and its bioindication--an overview

Man made electromagnetic irradiation and fields cover now the globe due to the recent extensive propagation of mobile telephony. The increased load affects animals and also plants. Especially birds have been studied. Humans are also sensitive. They are good bioindicators as epidemiological methods are available. Humans can also report symptoms which cannot be directly measured with presently available technologies. The nonionizing irradiation can as the ionizing one break the DNA, damage proteins, even increase the blood brain barrier permeability, disturb the night rest, cause fatigue and hormonal disturbances. An increase of the tumours of human head has been described in correlation with the long-term mobile phone use and on that side more exposed. The regulations covering mobile telephony are already about two decades old and need re-evaluation. The multitude of irradiation and the interaction of the different wavelength exposures, i.e., frequency sensitivity is poorly known at present. We should not forget the comparative studies of different species especially those which rely in their lives on electromagnetic orientation physiology. Some countries have issued warnings on the exposures of children. The producers of mobile technology have recently warned the users not to keep those devices in active stage in skin contact.

Magnetic resonance assessment of iron overload by separate measurement of tissue ferritin and hemosiderin iron

With transfusional iron overload, almost all the excess iron is sequestered intracellularly as rapidly mobilizable, dispersed, soluble ferritin iron, and as aggregated, insoluble hemosiderin iron for long-term storage. Established magnetic resonance imaging (MRI) indicators of tissue iron (R(2), R(2)*) are principally influenced by hemosiderin iron and change slowly, even with intensive iron chelation. Intracellular ferritin iron is evidently in equilibrium with the low-molecular-weight cytosolic iron pool that can change rapidly with iron chelation. We have developed a new MRI method to separately measure ferritin and hemosiderin iron, based on the non-monoexponential signal decay induced by aggregated iron in multiple-spin-echo sequences. We have initially validated the method in agarose phantoms and in human liver explants and shown the feasibility of its application in patients with thalassemia major. Measurement of tissue ferritin iron is a promising new means to rapidly evaluate the effectiveness of iron-chelating regimens.

Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteins

The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2 x 10(-6) m(3) kg(-1) and its Néel relaxation time at about 10(-10) s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30 microT at 1 MHz, as measured via Raman spectroscopy. After 2 h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale.

The Mössbauer and magnetic properties of ferritin cores

BACKGROUND

Mössbauer and magnetization measurements, singly or in combination, extract detailed information on the microscopic or internal magnetism of iron-based materials and their macroscopic or bulk magnetization. The combination of the two techniques affords a powerful investigatory probe into spin relaxation processes of nanosize magnetic systems. The ferritin core constitutes a paradigm of such nano-magnetic system where Mössbauer and magnetization studies have been broadly combined in order to elucidate its composition, the initial steps of iron nucleation and biomineralization, particle growth and core-size distribution. In vivo produced and in vitro reconstituted wild-type and variant ferritins have been extensively studied in order to elucidate structure/function correlations and ferritin's role in iron overloading or neurodegenerative disorders.

SCOPE OF REVIEW

Studies on the initial stages of iron biomineralization, biomimetic synthetic analogues and ferrous ion retention within the ferritin core are presented. The dynamical magnetic properties of ferritin by Mössbauer and magnetization measurements are critically reviewed. The focus is on experiments that reveal the internal magnetic structure of the ferritin core. Novel magnetic measurements on individual ferritin molecules via AFM and nanoSQUID investigations are also mentioned.

MAJOR CONCLUSIONS

A complex two-phase spin system is revealed due to finite-size effects and non-compensated spins at the surface of the anti-ferromagnetic ferritin core. Below the blocking temperature surface spins participate in relaxation processes much faster than those associated with collective magnetic excitations of interior spins.

GENERAL SIGNIFICANCE

The studies reviewed contribute uniquely to the elucidation of the spin-structure and spin-dynamics of anti-ferromagnetic nanolattices and their possible applications to nano/bio-technology.

Magneto-orientational behavior of a suspension of antiferromagnetic particles

A theory describing magneto-orientational properties of suspensions containing antiferromagnetic nanoparticles is developed. Due to their small size, these particles possess, apart from an anisotropic magnetic susceptibility pertinent to antiferromagnets, a spontaneous magnetic moment caused by sublattice decompensation. In a colloid subjected to a DC field of increasing strength an orientational crossover takes place: the particle magnetic moments, initially aligned along the field, turn to the transverse orientation. This behavior considerably changes the observable characteristics of the system: the spectrum of linear dynamic susceptibility and the integral time of magnetic relaxation under a pulse field.

The magnetic susceptibilities of iron deposits in thalassaemic spleen tissue

The iron-specific magnetic susceptibility of tissue iron deposits is used in the field of non-invasive measurement of tissue iron concentrations. It has generally been assumed to be a constant for all tissue and disease types. The iron-specific magnetic susceptibilities chi(Fe) for spleen tissue samples from 7 transfusion dependent beta-thalassaemia (beta-thal) patients and 11 non-transfusion dependent beta-thalassaemia/Haemoglobin E (beta/E) patients were measured at 37 degrees C. Both groups of patients were iron loaded with no significant difference in the distribution of spleen iron concentrations between the two groups. There was a significant difference between the mean chi(Fe) of the spleen tissue from each group. The non-transfusion dependent beta/E patients had a higher mean (+/-standard deviation) spleen chi(Fe) (1.55+/-0.23 x 10(-6) m(3)/kg Fe) than the transfusion dependent beta-thal patients (1.16+/-0.25 x 10(-6) m(3)/kg Fe). Correlations were observed between chi(Fe) of the spleen tissue and the fraction of magnetic hyperfine split sextet in the (57)Fe Mössbauer spectra of the tissues at 78 K (Spearman rank order correlation r=-0.54, p=0.03) and between chi(Fe) of the spleen tissue and the fraction of doublet in the spectra at 5 K (r=0.58, p=0.02) indicating that chi(Fe) of the spleen tissue is related to the chemical speciation of the iron deposits in the tissue.

Magnetic Langmuir-Blodgett films of ferritin with different iron contents

Magnetic Langmuir-Blodgett films of four ferritin derivatives with different iron contents containing 4220, 3062, 2200, and 1200 iron atoms, respectively, have been prepared by using the adsorption properties of a 6/1 mixed monolayer of methyl stearate (SME) and dioctadecyldimethylammonium bromide (DODA). The molecular organization of the mixed SME/DODA monolayer is strongly affected by the presence of the water-soluble protein in the subphase as shown by pi-A isotherms, BAM images, and imaging ellipsometry at the water-air interface. BAM images reveal the heterogeneity of this mixed monolayer at the air-water interface. We propose that the ferritin is located under the mixed matrix in those regions where the reflectivity is higher whereas the dark regions correspond to the matrix. Ellipsometric angle measurements performed in zones of different brightness of the mixed monolayer confirm such a heterogeneous distribution of the protein under the lipid matrix. Transfer of the monolayer onto different substrates allowed the preparation of multilayer LB films of ferritin. Both infrared and UV-vis spectroscopy indicate that ferritin molecules are incorporated within the LB films. AFM measurements show that the heterogeneous distribution of the ferritin at the water-air interface is maintained when it is transferred onto solid substrates. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, marked hysteresis loops of magnetization are obtained below 20 K with coercive fields that depend on the number of iron atoms of the ferritin derivative.

Methods for noninvasive measurement of tissue iron in Cooley's anemia

To examine the relationship between myocardial storage iron and body iron burden, as assessed by hepatic storage iron measurements, we studied 22 patients with transfusion-dependent thalassemia syndromes, all being treated with subcutaneous deferoxamine, and 6 healthy subjects. Study participants were examined with a Philips 1.5-T Intera scanner using three multiecho spin echo sequences with electrocardiographic triggering and respiratory navigator gating. Myocardial and hepatic storage iron concentrations were determined using a new magnetic resonance method that estimates total tissue iron stores by separately measuring the two principal forms of storage iron, ferritin and hemosiderin. In a subset of 10 patients with beta-thalassemia major, the hepatic storage iron concentration had been monitored repeatedly for 12-14 years by chemical analysis of tissue obtained by liver biopsy and by magnetic susceptometry. In this subset, we examine the relationship between hepatic iron concentration over time and our current magnetic resonance estimates of myocardial iron stores. No significant relationship was found between simultaneous estimates of myocardial and hepatic storage iron concentrations. By contrast, in the subset of 10 patients with beta-thalassemia major, the correlation between the 5-year average of hepatic iron concentration and the current myocardial storage iron was significant (R = .67, P = .03). In these patients, myocardial storage iron concentrations seem to reflect the control of body iron over a period of years. Magnetic resonance methods promise to provide more effective monitoring of iron deposition in vulnerable tissues, including the liver, heart, and endocrine organs, and could contribute to the development of iron-chelating regimens that more effectively prevent iron toxicity.

Bioinorganic transformations of liver iron deposits observed by tissue magnetic characterisation in a rat model

The magnetic properties and the ultrastructure, with special emphasis on the nanometric range, of liver tissues in an iron overload rat model have been investigated. The tissues of the animals, sacrificed at different times after a single iron dextran injection, have been characterised by magnetic AC susceptibility measurements together with transmission electron microscopy (TEM) and selected area electron diffraction (SAED) as helping techniques. It has been observed that few days after the iron administration the liver contains at least two iron species: (i) akaganéite nanoparticles, coming from iron dextran and (ii) ferrihydrite nanoparticles corresponding to ferritin. The magnetic susceptibility of the tissues depends not only on the elemental iron content but also on its distribution among chemical species, and varies in a remarkable regular manner as a function of the elapsed time since the iron administration. The results are of relevance with respect to non-invasive techniques for liver iron determination, directly or indirectly based on the magnetic susceptibility of the tissues, as biomagnetic liver susceptometry (BLS) and magnetic resonance (MRI) image treatment.

Magnetic characterisation of rat muscle tissues after subcutaneous iron dextran injection

Ex vivo freeze-dried rat muscle tissues, collected at different times t after a single dose of subcutaneously injected iron dextran, have been magnetically characterised. The AC susceptibility of the tissues shows an overall superparamagnetic behaviour and the dependence on t of, especially, the out-of-phase component is remarkably systematic despite the fact that each tissue originates in a different rat individual. The experiments show that the akaganéite (beta-FeOOH) nanoparticles contained in the injected drug are progressively degraded in the living tissue and, at times of the order of 1 month and for all the analysed rat individuals, converge to a magnetically well-defined species with much narrower magnetic activation energy distribution than iron dextran. Thorough transmission electron microscopy experiments of the same tissues indicate the presence of oxyhydroxide particles, whose size decreases for increasing t in agreement with the interpretation of the magnetic susceptibility. The conclusions drawn from the magnetic study do well correspond to the properties of the whole tissue since no biochemical extraction work has been done. The AC susceptibility appears to be a valuable and complementary tool in pharmacological studies of iron-containing drugs.

Characterization of iron compounds in tumour tissue from temporal lobe epilepsy patients using low temperature magnetic methods

Excess iron accumulation in the brain has been shown to be related to a variety of neurodegenerative diseases. However, identification and characterization of iron compounds in human tissue is difficult because concentrations are very low. For the first time, a combination of low temperature magnetic methods was used to characterize iron compounds in tumour tissue from patients with mesial temporal lobe epilepsy (MTLE). Induced magnetization as a function of temperature was measured between 2 and 140 K after cooling in zero-field and after cooling in a 50 mT field. These curves reveal an average blocking temperature for ferritin of 10 K and an anomaly due to magnetite at 48 K. Hysteresis measurements at 5 K show a high coercivity phase that is unsaturated at 7 T, which is typical for ferritin. Magnetite concentration was determined from the saturation remanent magnetization at 77 K. Hysteresis measurements at various temperatures were used to examine the magnetic blocking of magnetite and ferritin. Our results demonstrate that low temperature magnetic measurements provide a useful and sensitive tool for the characterisation of magnetic iron compounds in human tissue.

Study of the relationship of small variations of the molecular structure and the iron state in iron containing proteins by Mössbauer spectroscopy: biomedical approach

This review considers the results of experimental Mössbauer studies and theoretical calculations of the effect of small variations of protein molecular structure on the iron electronic structure and stereochemistry in order to understand the proteins structural heterogeneity and functional variety. Structural changes in iron containing proteins during various diseases are also considered. These results show the relationship of the small structural variations and Mössbauer parameters of iron containing proteins and demonstrate the possibilities of Mössbauer spectroscopy to obtain new information at the molecular level in biomedical research.

Biological tissue characterization by magnetic induction spectroscopy (MIS): requirements and limitations

Magnetic induction spectroscopy (MIS) aims at the contactless measurement of the passive electrical properties (PEP) sigma, epsilon, and mu of biological tissues via magnetic fields at multiple frequencies. Whereas previous publications focus on either the conductive or the magnetic aspect of inductive measurements, this article provides a synthesis of both concepts by discussing two different applications with the same measurement system: 1) monitoring of brain edema and 2) the estimation of hepatic iron stores in certain pathologies. We derived the equations to estimate the sensitivity of MIS as a function of the PEP of biological objects. The system requirements and possible systematic errors are analyzed for a MIS-channel using a planar gradiometer (PGRAD) as detector. We studied 4 important error sources: 1) moving conductors near the PGRAD; 2) thermal drifts of the PGRAD-parameters; 3) lateral displacements of the PGRAD; and 4) phase drifts in the receiver. All errors were compared with the desirable resolution. All errors affect the detected imaginary part (mainly related to sigma) of the measured complex field much less than the real part (mainly related to epsilon and mu). Hence, the presented technique renders possible the resolution of (patho-) physiological changes of the electrical conductivity when applying highly resolving hardware and elaborate signal processing. Changes of the magnetic permeability and permittivity in biological tissues are more complicated to deal with and may require chopping techniques, e.g., periodic movement of the object.

Theory of nonexponential NMR signal decay in liver with iron overload or superparamagnetic iron oxide particles

A quantitative theory is proposed for the nonexponential NMR proton signal decay observed in liver with iron overload or superparamagnetic iron oxide particles. This effect occurs for Carr-Purcell-Meiboom-Gill (CPMG) sequences and is argued to be a direct consequence of the strong magnetic field inhomogeneities generated by the iron, rather than being due to tissue compartments. An approximate mathematical form is given for the signal decay, which is fit to experimental data for samples of rat liver with iron oxide particles, for samples of marmoset liver with hemosiderosis, and for in vivo human liver with hereditary hemochromatosis. The fitting parameters obtained are consistent with the pattern of iron deposition determined from histology. For the case of hereditary hemochromatosis, a good correlation is found between a parameter characterizing the nonexponential decay and the iron concentration. Implications for practical MR quantification of hepatic iron are discussed.

Hyperfine interactions in the iron cores from various pharmaceutically important iron-dextran complexes and human ferritin: a comparative study by Mössbauer spectroscopy

Mössbauer spectroscopy has been used to study the hyperfine interactions in the iron cores of pharmaceutically important industrial and elaborated iron-dextran complexes (ferritin models) and human ferritin. Mössbauer spectra of frozen solutions and lyophilized samples of iron-dextran complexes at 87 K demonstrated magnetic, superparamagnetic and paramagnetic states of iron in various complexes. Mössbauer spectra of human ferritin in frozen solution and lyophilized form showed paramagnetic state of iron at 87 K. Small variations of Mössbauer hyperfine parameters were observed for different samples at 87 and 295 K, respectively, supposing the homogenous iron cores. The values of quadrupole splitting for iron-dextran complexes and ferritin in frozen solutions at 87 K varied from 0.639 to 0.744 mm/s while those of lyophilized samples at 87 K varied from 0.714 to 0.788 mm/s. The values of quadrupole splitting for iron-dextran complexes and ferritin in lyophilized form at 295 K varied from 0.687 to 0.741 mm/s. The values of hyperfine magnetic fields on the 57Fe nuclei in several iron-dextran complexes at 87 K varied from approximately 231 to approximately 485 kOe. These small variations of the hyperfine parameters were related to several types of the hydrous iron oxide microstructural modifications in the core and variations of the iron core size. The influence of lyophilization on the iron core structure was also assumed. In addition, Mössbauer spectra were evaluated in supposition of heterogeneous iron core in all samples.

Nanoscale biogenic iron oxides and neurodegenerative disease

One of the characteristics of many neurodegenerative diseases is the disruption of normal iron homeostasis in the brain. Recent experimental work indicates that nanoscale magnetic biominerals (primarily magnetite and maghemite) may be associated with senile plaques and tau filaments found in brain tissue affected by these diseases. These findings have important implications for our understanding of the role of iron in neurodegenerative disease as well as profound implications for their causes. In addition, the presence of biogenic magnetite in affected tissue should also provide improved mechanisms for early detection through the modification of MRI pulse sequences.