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A quick and easy method to detect the GDF-15 protein (Growth Differentiation Factor-15) has been developed, which utilize the magnetic response of magnetic nanoparticles by switching magnetic fields. The magnetic nanoparticles and GDF-15 are bound by an antigen-antibody reaction and aggregated into a spherical shape using a needle-shaped magnetic yoke. The density of GDF-15 changed as follows: 0, 1 ng/ml, 10 ng/ml, and 100 ng/ml. The increase of GDF-15 aggregated the magnetic nanoparticles and enhanced the signal-to-noise ratio. We also tried the sandwich-type bound method using a primary and secondary antibody with additional magnetic nanoparticles and obtained the enhancement of the magnetic signal in a lower concentration (under 10 ng/ml) of GDF-15. The cross-bridges between magnetic nanoparticle and the protein may strengthen the magnetic couplings of nanoparticles.

Dumbbell-shaped hybrid nanoparticles, consisting of gold and iron oxide (Au-Fe3O4 NPs), show promise for magnetic hyperthermia cancer therapy. However, conventional synthesis methods using toxic iron pentacarbonyl (Fe(CO)5) raise safety concerns. We propose a safer approach using triiron dodecacarbonyl (Fe3(CO)12) as a precursor. We synthesize these NPs by initially reducing gold (III) chloride trihydrate with a tert-butylamine-borane complex at room temperature, yielding Au NPs. These Au NPs are combined with a Fe3(CO)12 solution and heated to 300 °C for 1 hour, resulting in the desired dumbbell-shaped Au-Fe3O4 NPs. Characterization confirms their morphology, with average sizes of 5 nm for Au NPs and 15 nm for Fe3O4 NPs. Our systematic evaluation of hydrophilic-treated Au-Fe3O4 NPs (Ms=49.5 emu/g at 3T, 300K) demonstrates temperature increases beyond the therapeutic threshold of 45 °C (ΔT=8 °C) at higher field strengths (8.6–30.0 kA/m), highlighting their cancer treatment potential. Quantitative analysis reveals superb performance, with a specific absorption rate (SAR) of 60.0 W/g and intrinsic loss power (ILP) of 0.25 nHm2kg−1 at the maximum field strength. These findings emphasize the significant potential of our dumbbell-shaped Au–Fe3O4 NPs for magnetic hyperthermia.

We investigated the magnetization response and heat generation of magnetic particles exposed to high-speed pulsed magnetic fields (PMF) during magnetic hyperthermia cancer treatment. The magnetization measurements exhibited an asymmetric change in the shape of the hysteresis loop, attributable to the rapid and substantial changes in the short-duration PMF (75 mT/μs). We propose a novel parameter to evaluate heat efficiency. The parameter considered disparities in waveforms and served as a valuable metric for evaluating the effectiveness of heat production. Our findings affirmed a substantial enhancement in heat efficiency with the application of PMF. Furthermore, the heat generation stemming from the magnetic energy dissipation within the PMF exhibited direct proportionality to the square of the field amplitude. The heat efficiency is fourfold higher than that generated by conventional waveform.

We propose a novel method based on an inverse problem to design a single channel radio frequency (RF) receive coil for magnetic resonance imaging (MRI) with an optimized signal-to-noise ratio (SNR) for imaging the rat kidney. We identified a dedicated curved-surface coil design for use on the rat body surface utilizing inverse problem analysis using direct current calculation and quantitatively evaluated the indicators of coil performance using alternating current calculation. The proposed coil achieved increased SNR and signal intensity responses that were respectively 1.05- and 2-fold higher than those of conventional surface coils. In the future, we will fabricate a prototype coil and perform the MRI of the rat kidney to diagnose kidney diseases.

Ferromagnetic resonance (FMR) holds promise for heating magnetic nanoparticles (MNPs) in cancer therapy, especially for rapidly heating MNPs. This study aims to enhance the FMR-based heating efficiency of multifunctional hybrid gold and iron oxide nanoparticles (Au-Fe3O4 NPs) as theranostic agents. We experimentally investigate the FMR-based heating properties of newly developed dumbbell-like Au-Fe3O4 NPs, which feature ∼5 nm gold and 15 nm iron oxide components, in comparison to our previously developed Au-coated Fe3O4 NPs (Fe3O4 core ∼5.2 nm, Au shell thickness ∼0.5 nm). For comparison, we also synthesize pure Fe3O4 NPs (∼11 nm) under the same experimental conditions as the dumbbell-like Au-Fe3O4 NPs but without 5 nm Au seeds. Temperature measurements are taken at various DC fields (HDC = 0‒1600 Oe) under a radiofrequency (RF) field (fAC = 4 GHz, HAC = 1.265 Oe) for ∼13s. The results reveal a rapid temperature rise during RF field ON, followed by a decline upon RF field OFF. Remarkably, dumbbell-like Au-Fe3O4 NPs achieve a peak temperature increase of 23.4 °C, corresponding to a heating rate of 1.73 °C/s at HDC = 400 Oe, surpassing the combined values of ∼11 nm Fe3O4 NPs (11.0 °C, i.e., 0.83 °C/s at HDC = 1000 Oe) and ∼5 nm Au NPs (3.5 °C). Comparing these results to our previously developed Au-coated Fe3O4 NPs, which achieved a heating rate of 1.29 °C/s (temperature rise 16.9 °C) under HDC = 1200 Oe with an RF field at fAC = 4 GHz and a significantly higher HAC = 4 Oe (i.e. for HAC = 1.265 Oe, the estimated heating rate was 0.129 °C/s with a temperature rise of 1.69 °C), the dumbbell-shaped Au-Fe3O4 NPs demonstrate a substantially higher temperature increase by 13.4 times. These findings highlight the exceptional potential of dumbbell-shaped Au-Fe3O4 NPs for application in magnetic hyperthermia.

In this study, we prepared ultrasmall FeCo nanoparticles (NPs) with a high magnetic moment and examined their antigen-antibody reaction for biodetection applications. The FeCo NPs were collected from the FeCo-BaF2 nanogranular film with Fe:Co:Ba:F = 14:11:21:54 at.%, by dissolving the film in water since the BaF2 matrix was deliquescent. The size of FeCo NPs was ∼5 nm and the saturation magnetization was estimated to be ∼15.30 kG (149.0 emu/g). The Candida albicans antibodies (abcam ab53891)-conjugated FeCo NPs were collected by using an ultracentrifugal separation (110 000 rpm, 90 min), they were then reacted with Candida albicans. The obtained result indicates that Candida albicans were absorbed successfully onto FeCo NPs, and the number of Candida albicans bound to FeCo NPs counted from the micrographs of the aggregates of FeCo NPs and Candida albicans increased significantly by adding sonication treatment of the film in water before binding them to the antibodies. The success of antigen-antibody reaction of ultrasmall NPs with high magnetic moment improves detection sensitivity as well as offers potential detection for smaller biomolecules.

Alternating magnetic fields can deliver magnetic energy deeper inside the body for magnetic hyperthermia cancer therapy by using magnetic nanoparticles (MNPs). In this study, we proposed a highly effective heat generation method for the MNPs by the application of an ultra-short pulse wave. We numerically evaluated the heating power with a variety of parameters, such as pulse width, field amplitude, and frequency. The hysteresis curve and magnetization dynamics clearly indicate larger energy dissipation. Hysteresis loss and the input energy increase with increasing field strength and duty ratio and there is a large efficiency power condition. To evaluate the effective heat generation and practical temperature increment, a larger imaginary part of magnetic susceptibility (χ″ > 30) and specific loss power (SLP > 105 W/kg) are required. In addition, larger intrinsic loss power (100 nHm2/kg) is achieved. The results indicate that the contribution of magnetic harmonics signals on the ultra-short pulse wave significantly enhances the heat generation of MNPs for cancer therapy.

Virus detection methods based on nonlinear magnetic response of magnetic nanoparticles have been investigated, and magnetic detection methods using the third harmonic are widely applied, owing to their high sensitivity and short measurement time. This paper proposes a virus detection method based on the second harmonic because of its larger signal component. We found that the second harmonic signal is superior to the third harmonic signal for small nanobeads and a large change of the second harmonic signal in the signal-to-noise ratio (SNR) with nanobeads concentration. In addition, a virus detection limit of 100 pg/ml is achieved. Therefore, the proposed method can potentially be utilized for rapid screening of viruses.

Magnetic hyperthermia with magnetic nanoparticles (MNPs) has been introduced to selective treatment of tumor and the MNPs also has demonstrated diagnosis. For non-invasive treatment, a therapeutic platform with temperature monitoring that can avoid overheating in normal tissues is of vital importance. In this study, we have developed a wireless temperature monitoring system by utilizing the combination of magnetic harmonic signals of the MNPs for magnetic hyperthermia treatment in laboratory experiments. We achieved an accurate measurement with an error of 0.18 °C. For practical use on breast/oral cancer, a detectable distance of at least 10 mm is required. To demonstrate the feasibility toward future biomedical applications, we investigated the dependency on the amount of Resovist® and the error is less than 0.5 °C in a 10 mm distance. Our system can measure the correct temperature regardless of Resovist amount. The results indicate that our system can apply for monitoring temperature on magnetic hyperthermia treatment.

We have proposed coplanar line type thin-film magnetic field sensor with narrow slits. The slit is employed to flow more carrier current on the signal line by improving the impedance matching. Several sensors having 6, 10, 26, 36, and 50 μm slit widths were fabricated and evaluated from the phase and the amplitude of the transmission coefficient (S21) and reflection coefficient (S11) measured by the network analyzer. The amplitude of S21 with slit was improved about five times larger than the sensor without one at around 2 GHz. The appropriate slit width was evaluated as around 10 μm for the coplanar line type thin film magnetic field sensor and the sensitivity will enhance more than 10 times higher than the sensor without slits.

A novel method for measuring the complex magnetic susceptibility of magnetic nanoparticles (MNPs) has been developed by a broadband microstrip line-type probe with a frequency range of up to 50 GHz. Two external orthogonal DC fields, Hhard and Heasy, were applied to change the susceptibility of MNPs (Streptavidin coated, 200 nmϕ, number of MNPs about 1010) based on magnetization switching theory. The susceptibility of MNPs in the liquid, solid state, and after biotin-avidin reaction with polymer beads (2 μmϕ, number of polymer beads about 108) was evaluated. A clear FMR frequency of MNPs and the same FMR frequency shift trend as Hhard changed was observed around 2–10 GHz in both liquid and solid states. The susceptibility of MNPs reached maximum when Hhard was 0.1 T which is approximately equal to Heasy (0.135 T). The maximum values of real and imaginary parts increased by a factor of 3.39 and 1.66 compared to when Hhard was 0. The obtained results indicate that the magnetic anisotropy was successfully controlled in the liquid and solid states of MNPs aggregate. Furthermore, after the biotin-avidin reaction of MNPs with polymer beads, the imaginary part of susceptibility showed a decreasing trend regardless of the increase in Hhard, and its half-width expanded by 35.1% at maximum when Hhard was 0.15 T.

In this study, we aim to develop gold-coated Fe3O4 nanoparticles (Fe3O4@Au NPs) as theranostic agents for magnetic hyperthermia and CT imaging applications. The Fe3O4 NPs were synthesized via thermal decomposition method, and the gold was then deposited onto the surface of Fe3O4 NPs by reducing gold acetate at 190 °C. The average sizes of Fe3O4 and Fe3O4@Au NPs were 5.2 nm and 6.1 nm, respectively, which are effectively removed by the kidneys. The magnetization of Fe3O4@Au NPs (9.7 emu/g-Fe3O4) at 300 K was much smaller than that of Fe3O4 NPs (52.4 emu/g-Fe3O4). The heating efficiency of Fe3O4@Au NPs in water was sufficient to treat the tumor at 43–45 °C, and their high CT value of 851 HU was obtained. The synthesized ultrasmall Fe3O4@Au NPs showed great promise as a potential theranostic agent for magnetic hyperthermia and CT imaging applications.

We propose a novel method based on the inverse problem approach to optimize the shape of a magnet generates high uniformity of magnetic fields in a magnetometer with diamond nitrogen-vacancy (NV) centers. Our original method can determine the combination of magnetic moments required to design a unique magnet shape. We obtained a unique shape of the small magnet (optimized model, 15 × 15 × 25 mm3 and 25 × 25 × 15 mm3) for integrated magnetometry system and improved the magnetic uniformity from 83.6% to 99.0% in the diamond NV centers area (X = −1–1 mm, Y = −1–1 mm, Z = 5–6 mm). The results indicate a highly sensitive magnetometer with a diamond NV center for future biomedical applications.

Abstract We have fabricated a high quality magnetic Ni0.5Zn0.5Fe2O4 ferrite powder/polymer composite sheet consisting of common and environmentally friendly elements only. The sheet was then tested for its dynamic permeability by irradiating with electromagnetic waves with frequencies up to 50 GHz. Two different originally developed methods were used for the high-frequency permeability measurements, a short-circuited microstrip line method and a microstrip line-probe method. It is challenging to measure the dynamic permeability of magnetic thin films/sheets beyond 10 GHz because of the low response signal from these materials. However, the two methods produced essentially equivalent results. In the frequency dependent permeability profile, the maximum position of the profile, $$\mu ^{\prime \prime }_{max}$$ μ max ″ , shifted towards higher frequencies upon increasing an applied (strong) static external magnetic field, $$H_{dc}$$ H dc . A linear relationship between $$\mu^ {\prime \prime }_{max}$$ μ max ″ and $$H_{dc}$$ H dc for the entire range of $$H_{dc}$$ H dc was observed even at small $$H_{dc}$$ H dc . In general, the spinel-structured Ni-based ferrites exhibit low magnetic anisotropy, but the present sample showed a uniaxial-anisotropic behavior in the parallel direction of the sheet. Our Ni0.5Zn0.5Fe2O4 powder/polymer composite sheet thus exhibits high performance at GHz frequencies, and should be applicable e.g. as an anisotropic electromagnetic wave-interference material.

Hyperthermia using magnetic particles is a very promising cancer therapy. In previous studies, we developed a mixture of magnetic micro/nanoparticles with high heating efficiency for tumor treatment and considerable change in permeability around therapeutic temperature for monitoring its temperature and position during heating. In this study, we examined experimentally the effect of applied magnetic field on the heating and permeability properties of the proposed mixture by manipulating the amplitude and frequency (H = 1.8–7.1 kA/m, f = 500 kHz, and H = 4.8 kA/m, f = 200–1000 kHz). It was found that the specific absorption rate (SAR) of the mixture increased with the amplitude and frequency (SAR α H1.68×f). Its intensity of magnetization (μ0M) at 20°C changed linearly with the amplitude, whereas it remained almost unchanged with the frequency. The results obtained here may enable us to find the optimal conditions of the applied magnetic field and the amount of magnetic particles required to treat a tumor of a given size.

This study describes a user-friendly and rapid detection system of oral bacteria in the liquid phase for point of care testing based on magnetic immunoassay. We focused on the dependence of the strength of external magnetic field required to switch the magnetic moments of nanoparticles bound to bacteria on the bacteria concentration. The results obtained indicate that the required field strength increases linearly as a function of log concentration of Porphyromonas gingivalis cultured in the range of 103–109 CFU/mL. Similarly, the required field strengths for Streptococcus mutans and Pseudomonas aeruginosa increase monotonically when their concentrations increase, whereas the required field strength for Escherichia coli decreases monotonically when its concentration increases. We then measured the concentration of Porphyromonas gingivalis in the saliva collected from elderly people in a geriatric health services facility and the results using the developed system had a correlation with those using a commercial bacteria counter.

An interesting behavior of thin-film magnetoimpedance elements in the relatively low megahertz (MHz) region is found experimentally when the width of the element is narrow and the thickness of elements is several micrometers. The impedance peaks and inductance shows a rapid drop at around 10 MHz when a bias field is applied to such elements. The impedance profiles of the elements were analyzed on the basis of a domain wall motion equation and bias susceptibility theory. Calculation of the domain wall motion equation when accounting for domain resonance explains the impedance behavior in the low MHz region. The rapid drop in inductance and peak in impedance can be attributed to the domain wall resonance. At a relatively higher frequency, above 100 MHz, the calculation of bias susceptibility while considering ferromagnetic resonance thoroughly explains the experimental behavior.

We fabricated thin-film magnetoimpedance elements in which an impedance of each 100 μm section of element can be examined, to investigate impedance changes of each section subjected to a DC magnetic field. The field strength where the impedance peaks shows a larger value at the edge and it decreases toward the center of the element, while the sensitivity is small at the end of the elements and increases toward the center of the element. The obtained results can be explained on a basis of magnetic field simulation and simple impedance model taking into account a distribution of demagnetizing field. A uniformity of demagnetizing field is significant to obtain a higher sensitivity, and intensity of the demagnetizing field strongly affects a magnetic field strength when the impedance peaks. We also clarified an ellipsoidal shape uniform the distribution of demagnetizing field within the element, which contributes to improve the sensitivity of the MI sensor, especially near edge part.