Concentration Of Magnetic Nanoparticles Research Articles

Amoeba-Inspired Soft Robot for Integrated Tumor/Infection Therapy and Painless Postoperative Drainage.

Tumor recurrence and wound infection are devastating complications of wide excision surgery for melanoma, and deep postoperative wound drainage typically increases pain. An amoeba-inspired magnetic soft robot (ASR) with switchable dormant and active phases is developed to address the aforementioned challenges. The dormant ASR supports wounds through its solid-like elasticity and regulates reactive oxygen species (ROS) levels bidirectionally, promoting healing in infected wounds and eliminating residual tumors. It solves the challenge caused by the contradictory need for ROS scavenging in wound healing and ROS amplification in tumor/infection management. The active ASR removes absorbed wound exudate by crawling out from irregular wounds; interestingly, this crawling motion prevents damage to fragile tissues and alleviates wound pain via "non-direct friction." More importantly, ASR switches different states in response to an alternating magnetic field owing to its magnetothermal properties, and this process also exerts synergistic antitumor and bacteriostatic effects. Due to the appropriate mechanical structure (cohesive force) of ASR, the content of magnetic nanoparticles required to drive the ASR is ten-fold lower than that of conventional magnetic soft robots, enabling in vivo degradation. These outcomes highlight the vantage of the ASR for treating post-tumor excision wounds and underscore their potential for clinical application.

Sensitivity study of heat transfer in a Jeffrey ferro-hybrid nanofluid bioconvective squeezing flow with inclined MHD and higher-order chemical reaction: entropy analysis

Abstract The present investigation concentrates on analyzing heat transfer and entropy formation in a time-reliant bioconvective flow of a blood-based Jeffrey hybrid nanofluid via a squeezing channel that is suctioned or injected at the lower plate. Cu nanoparticles and Fe3O4 ferro-nanoparticles are suspended in base-fluid blood. Adding ferro-nanoparticles to a flow process allows for better control of the external magnetic field and improved heat transmission. Noble integration of an aligned magnetic field, Joule's heating, thermal radiation, and higher-order chemical reactions is taken into account in the flow in a porous media. An appropriate choice of similarity variables leads to the non-dimensionalization of the governing equations, that are subsequently solved by the homotopy analysis method (HAM), yielding a semi-analytical solution. An innovative feature of this research is the optimization of heat transfer by the application of the response surface methodology (RSM) technique. Additionally, sensitivity analysis was carried out to identify the most influential parameter. The study's findings indicate that increased suction reduces both velocity and temperature distributions in both the nanofluid and hybrid nanofluid models. In terms of thermal performance, the Blood/Fe3O4 - Cu hybrid nanofluid surpasses the Blood/Fe3O4 nanofluid. The rate of thermal energy transfer is highly sensitive to variations in the Eckert number, while thermal radiation has a relatively lesser impact. Moreover, elevated levels of the magnetic parameter, Eckert number, and nanoparticle concentration lead to augmented entropy formation. This mathematical model is effective for analyzing drug transport mechanisms throughout the human body and presents extensive potential applications in the fields of biology and healthcare.

Simulation study on magneto-acoustic concentration tomography of magnetic nanoparticles based on vectorial acoustic source and BICGSTAB method

Abstract To overcome the vulnerability to noise of the reconstructed image and simplify the cumbersome iteration process of algorithm in the magneto-acoustic concentration tomography with magnetic induction (MACT-MI) for magnetic nanoparticles (MNPs), we established the matrix relationship between the concentration of MNPs and the first-order derivative of sound pressure based on the reconstruction method of vectorial acoustic source, and proposed the application of BICGSTAB method in solving the concentration distribution. Firstly, a simulation model was established in COMSOL Multiphysics. Secondly, the obtained data were substituted into the derived formula for imaging reconstruction. Finally, the quality of the reconstructed image was analyzed. The effects of MNP radius, shape, asymptotic concentration, and SNR on the reconstruction results were studied. Simulation results show that under the same noise condition, compared with the reconstruction method based on the LSQR-trapezoidal method, the average correlation coefficient increased by 32.9%, the average relative error decreased by 48.5%, the average structural similarity increased by 48.2%, and the average iterations decreased by 58.5%. The proposed method shows superior imaging quality and noise immunity. The research provides a theoretical basis for subsequent experimental research.

Ranking Magnetic Colloid Performance for Magnetic Particle Imaging and Magnetic Particle Hyperthermia

AbstractMagnetic particle imaging (MPI) is an emerging modality that can address longstanding technological challenges encountered with magnetic particle hyperthermia (MPH) cancer therapy. MPI is a tracer technology compatible with MPH for which magnetic nanoparticles (MNPs) provide signal for MPI and heat for MPH. Identifying whether a specific MNP formulation is suitable for both modalities is essential for clinical implementation. Current models predict that functional requirements of each modality impose conflicting demands on nanoparticle magnetic properties. This objective here is to develop a measurement and ranking scheme based on end‐use performance to streamline evaluation of candidate MNP formulations. The measured MPI point‐spread function (PSF) and specific loss power (SLP) is combined to generate a single numerical value for comparison on a relative ranking scale, or figure of merit (FoM). 12 aqueous iron‐containing formulations are evaluated, including FDA‐approved (parenteral) iron‐containing colloids. MNPs with high (Synomag‐D70: 123.4), medium (Synomag‐D50: 63.2), and low (NanoXact: 0.147) FoM values are selected for in vivo validation of the selection scheme in subcutaneous 4T1 tumors. Results demonstrate that the proposed ranking accurately assessed the relative performance of MNPs for MPI and MPH. Data demonstrated that image quality and tumor temperature rise increased with FoM ranking, validating predictions. It isshown that the MPI signal correlated with MNP concentration in tissue. Computational heat transfer models anchored on tumor MPI data harmonized with experimental results to within an average of 2 °C when MNP content estimated from MPI data is included. Computational studies emphasized the importance of post‐injection MNP quantitation and MPI spatial resolution.

3D-printed polycaprolactone-magnetic nanoparticles composite multifunctional scaffolds for bone tissue regeneration and hyperthermia treatment

Cancer management after tumor resection is characterized by two critical needs: (i) rehabilitation of the resected tissue and (ii) preventing post-surgical tumor recurrence by destroying any residual tumors. The state of the art in literature is limited because it tackles these two major priorities individually, it achieves tissue regeneration via autologous grafting and prevents tumor recurrence through chemotherapy. In this paper, extrusion 3D printing has been employed to manufacture composite multi-functional scaffolds with polycaprolactone (PCL) as a polymeric matrix and magnetic nanoparticles (MNPs) in a 0 to 50 wt% ratio, that would aid in bone regeneration and cancer management via magnetic hyperthermia treatment. The fabricated scaffolds were evaluated for their mechanical, magnetic and thermal characteristics. The Young’s modulus of the scaffolds increased multi-fold with increasing concentration of MNPs added to PCL (26.88±9.02 MPa for pure PCL to 229.06±37.05 MPa for PCL/50 wt% MNP scaffolds). PCL/MNP scaffolds displayed a directly proportional correlation between MNP concentration and saturation magnetization. While the in vitro tests showed a statistically significant cell growth of human Mesenchymal Stem Cells (hMSCs) over 7 days for all MNP concentrations, only the 50% MNP scaffold showed an increase in temperature over 41oC when subjected to an alternating magnetic field making it suitable for the hyperthermia treatment. On application of alternating magnetic fields to PCL and PCL/50 wt% MNP scaffolds, there was an increase in hMSCs proliferation and decrease in Bone cancer cells proliferation, thus proving the potential to be used as a multi-functional scaffold for post-surgical bone cancer management.  

In Silico Approach to Model Heat Distribution of Magnetic Hyperthermia in the Tumoral and Healthy Vascular Network Using Tumor-on-a-Chip to Evaluate Effective Therapy.

Glioblastoma multiforme (GBM) is the most severe form of brain cancer in adults, characterized by its complex vascular network that contributes to resistance to conventional therapies. Thermal therapies, such as magnetic hyperthermia (MHT), emerge as promising alternatives, using heat to selectively target tumor cells while minimizing damage to healthy tissues. The organ-on-a-chip can replicate this complex vascular network of GBM, allowing for detailed investigations of heat dissipation in MHT, while computational simulations refine treatment parameters. In this in silico study, tumor-on-a-chip models were used to optimize MHT therapy by comparing heat dissipation in normal and abnormal vascular networks, considering geometries, flow rates, and concentrations of magnetic nanoparticles (MNPs). In the high vascular complexity model, the maximum velocity was 19 times lower than in the normal vasculature model and 4 times lower than in the low-complexity tumor model, highlighting the influence of vascular complexity on velocity and temperature distribution. The MHT simulation showed greater heat intensity in the central region, with a flow rate of 1 µL/min and 0.5 mg/mL of MNPs being the best conditions to achieve the therapeutic temperature. The complex vasculature model had the lowest heat dissipation, reaching 44.15 °C, compared to 42.01 °C in the low-complexity model and 37.80 °C in the normal model. These results show that greater vascular complexity improves heat retention, making it essential to consider this heterogeneity to optimize MHT treatment. Therefore, for an efficient MHT process, it is necessary to simulate ideal blood flow and MNP conditions to ensure heat retention at the tumor site, considering its irregular vascularization and heat dissipation for effective destruction.

Tunable electrical/thermal output performance of the PV/T system with magnetic nanofluid based spectral beam filter

The photovoltaic/thermal systems with magnetic nanofluid based spectral beam filter would achieve thermal decoupling and utilize the full spectrum to minimize energy loss. The prepared Fe3O4 magnetic nanofluid was introduced into this system as selective absorbing fluid filter. An external magnetic field was added to manipulate the distribution behavior of nanoparticles that affect the optical characteristics of magnetic nanofluids could meet the various application requirements for electrical/thermal output of the photovoltaic/thermal system. The optical properties of magnetic nanofluid with various nanoparticle distribution behaviors under the varying magnetic field were tested by UV–visible spectrophotometric and Finite-Difference Time-Domain simulated respectively. Furthermore, the effect of magnetic nanoparticle concentration and magnetic field strength on the electrical/thermal output performance of the photovoltaic/thermal system was studied. The results show the higher nanoparticle concentration enhances the thermal output of the system but reduces the electrical output, accompanied by a significant reduction in the surface temperature of the cell. Both photothermal and photovoltaic conversion efficiencies are increased below 100mT magnetic field due to the transmission in the response spectrum of monocrystalline silicon cell increase under the formation of chain structure of the nanoparticles. It is concluded that the photothermal, photovoltaic, and total solar energy conversion efficiencies are respectively 59.82%, 13.98%, and 73.75% at 0.0025 wt% concentration under 100 mT magnetic fields, and its function of merit value was increased by 109% compared to the system without spectral beam filter.

Magneto-Enzymatic Microgels for Precise Hydrogel Sculpturing.

The inclusion of hollow channels in tissue-engineered hydrogels is crucial for mimicking the natural physiological conditions and facilitating the delivery of nutrients and oxygen to cells. Although bio-fabrication techniques provide diverse strategies to create these channels, many require sophisticated equipment and time-consuming protocols. Herein, collagenase, a degrading agent for methacrylated gelatin hydrogels, and magnetic nanoparticles (MNPs) are combined and processed into enzymatically active spherical structures using a straightforward oil bath emulsion methodology. The generated microgels are then used to microfabricate channels within biomimetic hydrogels via a novel sculpturing approach that relied on the precise coupling of protein-enzyme pairs (for controlled local degradation) and magnetic actuation (for directional control). Results show that the sculpting velocity can be tailored by adjusting the magnetic field intensity or concentration of MNPs within the microgels. Additionally, varying the magnetic field position or microgel size generated diverse trajectories and channels of different widths. This innovative technology improves the viability of encapsulated cells through enhanced medium transport, outperforming non-sculpted hydrogels and offering new perspectives for hydrogel vascularization and drug/biomolecule administration. Ultimately, this novel concept can help design fully controlled channels in hydrogels or soft materials, even those with complex tortuosity, in a single wireless top-down biocompatible step.

A Novel Local Magnetic Fluid Hyperthermia Based on High Gradient Field Guided by Magnetic Particle Imaging.

Magnetic Particle Imaging (MPI)-guided Magnetic Fluid Hyperthermia (MFH) has the potential for widespread utilization, as it allows for the prediction of magnetothermal dosage, real-time visualization of the thermal therapy process, and precise localization of the lesion area. However, the existing MPI-guided MFH (MPI-MFH) method is insensitive to concentration gradients of magnetic nanoparticles (MNPs) and is susceptible to causing damage to normal tissues with high MNP concentrations during MFH treatment, while inadequately heating tumor tissues with lower MNP concentrations. In this work, we established a relationship between MNP concentration and heating efficiency through simulations and phantom measurements, enabling the optimal selection of MFH parameters guided by MPI. Based on these findings, we developed a high-gradient field MPI-MFH method using a field-free point (FFP) approach to achieve precise local heating. Phantom experiments and in vivo glioma model experiments were conducted to validate this proposed method. The results demonstrated that the proposed method of MPI-MFH can improve the MNP concentration gradient sensitivity to ±1 mg/ml, thereby enabling more effective lesion-site heating without damaging normal tissues. This method not only reduced glioma size effectively but also holds promise for application in various other types of cancers.

In Vitro Superparamagnetic Hyperthermia Employing Magnetite Gamma-Cyclodextrin Nanobioconjugates for Human Squamous Skin Carcinoma Therapy.

In vitro alternative therapy of human epidermoid squamous carcinoma (A431) by superparamagnetic hyperthermia (SPMHT) using Fe3O4 (magnetite) superparamagnetic nanoparticles (SPIONs) with an average diameter of 15.8 nm, bioconjugated with hydroxypropyl gamma-cyclodextrins (HP-γ-CDs) by means of polyacrylic acid (PAA) biopolymer, is presented in this paper. The therapy was carried out at a temperature of 43 °C for 30 min using the concentrations of Fe3O4 ferrimagnetic nanoparticles from nanobioconjugates of 1, 5, and 10 mg/mL nanoparticles in cell suspension, which were previously found by us to be non-toxic for healthy cells (cell viabilities close to 100%), according to ISO standards (cell viability must be greater than 70%). The temperature for the in vitro therapy was obtained by the safe application (without exceeding the biological limit and cellular damage) of an alternating magnetic field with a frequency of 312.4 kHz and amplitudes of 168, 208, and 370 G, depending on the concentration of the magnetic nanoparticles. The optimal concentration of magnetic nanoparticles in suspension was found experimentally. The results obtained after the treatment show its high effectiveness in destroying the A431 tumor cells, up to 83%, with the possibility of increasing even more, which demonstrates the viability of the SPMHT method with Fe3O4-PAA-(HP-γ-CDs) nanobioconjugates for human squamous cancer therapy.

3D Simulation-Driven Design of a Microfluidic Immunosensor for Real-Time Monitoring of Sweat Biomarkers.

This study presents the design and comprehensive 3D multiphysics simulation of a novel microfluidic immunosensor for non-invasive, real-time detection of pro-inflammatory biomarkers in human sweat. The patch-like device integrates magnetofluidic manipulation of antibody-functionalized magnetic nanoparticles (MNPs) with direct-field capacitive sensing (DF-CS). This unique combination enhances sensitivity, reduces parasitic capacitance, and enables a more compact design compared to traditional fringing-field approaches. A comprehensive 3D multiphysics simulation of the device, performed using COMSOL Multiphysics, demonstrates its operating principle by analyzing the sensor's response to changes in the dielectric properties of the medium due to the presence of magnetic nanoparticles. The simulation reveals a sensitivity of 42.48% at 85% MNP occupancy within the detection zone, highlighting the sensor's ability to detect variations in MNP concentration, and thus indirectly infer biomarker levels, with high precision. This innovative integration of magnetofluidic manipulation and DF-CS offers a promising new paradigm for continuous, non-invasive health monitoring, with potential applications in point-of-care diagnostics, personalized medicine, and preventive healthcare.

Spatially Confined Assembly and Immobilization of Hierarchical Nanoparticle Architectures inside Microdroplets in Magnetic Fields.

Magnetic field-directed colloidal interactions offer facile tools for assembly of structures that range from linear chains to multidimensional hierarchical architectures. While the field-driven assembly of colloidal particles has commonly been investigated in unbounded media, a knowledge gap remains concerning such assembly in confined microenvironments. Here, we investigate how confinement of ferromagnetic nanoparticles in microspheres directs their magnetic assembly into hierarchical architectures. Microdroplets from polydimethylsiloxane (PDMS) liquid precursor containing dispersed iron oxide magnetic nanoparticles (MNPs) were placed in a static magnetic field leading to the formation of organized assemblies inside the host droplets. By changing the MNP concentrations, we revealed a sequence of microstructures inside the droplets, ranging from linear chains at a low MNP loading, transitioning to a combination of chains and networked bundles, to solely 3D bundles at high MNP loading. These experimental results were analyzed with the aid of COMSOL simulations where we calculated the potential energy to identify the preferred assembly conformations. The chains at high MNP loading minimized their energy by aggregating laterally to form bundles with their MNP dipoles being out-of-registry. We cured these PDMS droplets to immobilize the assemblies by forming soft microbeads. These microbeads constitute an "interaction toolbox" with different magnetic macroscale responses, which are governed by the structuring of the MNPs and their magnetic polarizability. We show that thanks to their ability to rotate by field-induced torque under a rotating field, these microbeads can be employed in applications such as optical modulators and microrollers.

Formulation and Characterization of Ferrogels Based on Agar Gum and Octenyl Succinic Anhydride (OSA) Starch

AbstractPhysicochemical and rheological analyses are carried out on ferrogels based on Agar gum in combination with octenyl succinic anhydride (OSA) starch in the presence of magnetic nanoparticles (MNPs) coated with a stabilizing agent (PNiPAAm). The objective of this work is to prepare nanocapsules of MNPs coated with OSA starch present in a rigid network of Agar to obtain a nanocomposite gel (ferrogel). It is found that the effect of MNPs on the properties of ferrogels has a direct relationship with PNiPAAm/OSA starch interactions. The results obtained show that the ferrogels have stable thermal properties and a high melting point (99.7 °C) for high concentrations of MNPs (0.1%). The rheological properties show that this concentration (0.1%) has a negative effect on the crosslinking of Agar, therefore a drop in viscosity. In addition, it is shown that each pore comprises three populations of MNPs (primary: 3–4 nm, secondary: 6–9 nm, and clusters: ≥12 nm). Moreover, it is found that MNPs are coated with OSA starch. In addition, the prepared materials possess at low concentration of MNPs an interesting stiffness and uniform surface morphology with a minimum of clusters leading to stable systems that can be used as biomaterials in nanomedecine.

Experimental and statistical investigation on the dielectric breakdown of magneto nanofluids for power applications

The insulating oil serves the dual purpose of providing insulation and cooling within transformers. This investigation aims to explore the impact of various nanoparticles on the dielectric breakdown voltage (BDV) of dielectric oils. The study examines the effect of the concentration of magnetic nanoparticles on the dielectric breakdown voltage of insulating oils. Nanoparticles such as iron (II, III) oxide (Fe3O4), cobalt (II, III) oxide (CO3O4), and ferrous phosphide (Fe3P) were utilized to create nanofluids with carrier mediums consisting of mineral oil and synthetic ester oil. BDV determination was conducted using a VDE and S–S electrode system according to IEC 60156 standards. Nanofluid were prepared using a two-step method, and their concentrations ranged from 0.01 g/L, 0.02 g/L, and 0.04 g/L in base oils. Twelve iterations were conducted for each prepared nanofluid, and breakdown voltage measurements were recorded. The results indicate a noteworthy enhancement in the breakdown voltage of nanofluids. The statistical analysis was performed on the dielectric property of nanofluid samples for better breakdown accuracy. The maximum enhancement at specific nanoparticle concentrations was shown by each nanofluid. The results show that under the S–S electrode configuration, the greatest overall enhancement was observed for Fe3P in mineral oil, with an enhancement of 70.05%, and Fe3O4 in synthetic ester oil, with an enhancement of 46.29%.

Effects of magnetic fields and nanoparticle concentration on hydro-thermal performance of a surface enhanced microchannel

This article numerically investigates fluid flow and heat transfer in plain wall (PWMC) and oblique fin (OFMC) microchannels under varying magnetic fields using water- Al2O3 nanofluid as a working fluid. Effects of magnetic flux (Hartmann number, Ha = 0–30), fluid velocity (Reynolds number, Re = 100–500), and nanoparticle volume fraction (ϕ = 0%–2%) on the overall thermo-fluid performance are analyzed. Magnetic fields can significantly improve the heat transfer in OFMC in a higher rate compared to the PWMC. Also, there is a less increment on the pressure drop in the OFMC in comparison to PWMC. In addition, individual, as well as combined effect of Joule and viscous heating on the thermo-fluid performance is investigated. Due to the combined effect of Joule and viscous heating, the Performance Evaluation Criterion (PEC) in OFMC can be improved by 21%. However, the PEC in OFMC can be enhanced by 55% without considering the combined effect. The detailed characteristics flow and heat transfer are also studied by analyzing the velocity contours, isotherms, streamlines, friction factors, and Nusselt numbers. The present study concludes the importance of consideration of Joule and viscous heating for an accurate modeling, where the viscous heating plays the dominant role. The present findings can be instrumental in enhancing the performance of micro heat sinks to optimize hydrothermal performance in high powered motors, nuclear fusion reactors etc., where magnetic field is present.

Optimizing the magnetic field strength and concentration of silica coated cobalt ferrite nanoparticles for magnetic hyperthermia

A therapeutic breakthrough in cancer treatment has recently been made by using magnetic nanoparticles (MNPs) for heating in hyperthermia therapy. Unapproachable tumors are being effectively destroyed by focused heat produced by MNPs. The major challenges regarding practical application of this therapy include the control and improvement of induction heating ability of MNPs and hyperthermia temperature range between 42–47 °C, for secure treatment at targeted area. Here, in this study, we have reported the synthesis and characterization of core–shell structured silica-coated cobalt ferrite nanoparticles (SiO2 coated CoFe2O4 MNPs), which are potential candidates for use as heat source in magnetic hyperthermia therapy. The SiO2 coated CoFe2O4 MNPs were synthesized using the reverse micelle method, with the SiO2 coating performed simultaneously during MNP synthesis. Various analytical tools were utilized for the characterization. The structural measurements were probed by X-ray diffraction (XRD). Monodisperse MNPs with nearly spherical core–shell structure was revealed by Transmission electron microscopy (TEM) results. The average diameter of MNPs obtained from TEM analysis was 15 nm. The surface coating of cobalt ferrite MNPs with silica was verified by Fourier transform infrared spectrometry (FTIR). The saturation magnetization values obtained using vibrating sample magnetometer (VSM) measurements were 45.74 emu/g, revealing the superparamagnetic nature of the nanoparticles. The heating efficiency of different concentrations of synthesized nanoparticles was evaluated in an aqueous solution under an alternating magnetic field of strength 5.5 kA/m at a frequency of 260 kHz. A saturation temperature of 42 °C was attained at an optimum concentration of 1.7 mg/mL, while a magnetic field strength of 3.9 kA/m achieved 42 °C at a fixed concentration of 3.5 mg/ml. The obtained specific absorption rate (SAR) values for all the samples were between 56.23 to 100.1 W/g. The correlation between SAR values, MNP concentration, and applied magnetic field strength was also examined. The high saturation magnetization, efficient heating rates, and high SAR values make our synthesized silica-coated cobalt ferrite nanoparticles promising candidates for magnetic hyperthermia treatments, potentially improving therapeutic outcomes for cancer patients.

Investigating the effect of magnetic field and nanoparticles characteristics in the treatment of glioblastoma by magnetic hyperthermia method: An in silico study

This study investigated the use of magnetic fluid hyperthermia (MFH) for treating glioblastoma multiforme (GBM), a deadly and treatment-resistant tumor. It considers the effects of magnetic nanoparticle (MNP) (different sizes and materials), alternating magnetic field (AMF) characteristics (frequency and strength magnetic field), MFH duration, and injection number, using a realistic brain phantom, considering its blood circulation system, tumor, and healthy tissue properties. Results demonstrated that MFH is more sensitive to frequency, increasing frequency causing greater temperature and thermoablation than increasing strength magnetic field. The magnetic field strength can be increased at a fixed frequency to control temperature increase in mild hyperthermia treatment more reliably. The size of MNP significantly impacts temperature when exceeding 15.8 nm, while smaller particles do not significantly affect the temperature obtained. Also, the tumor's MNP concentration increases and uniformly disperses as the number of injection sites increases. The study examined the duration of hyperthermia treatment (30–60 min), it is important to optimize the duration to prevent irreparable damage in cases of temperature increase from 46 °C. In conclusion, to effectively manage the temperature generated and destruction of malignant tissue while minimizing damage to healthy tissue, multiple hyperthermia-related parameters must be adjusted simultaneously.

Research on Spatial Magnetic Field Distribution of Magnetic Fluids Based on Microstructure.

This study focuses on the spatial magnetic field distribution of magnetic fluids, an extraordinary class of fluids composed of magnetic nanoparticles (MNPs), employing the Monte Carlo method to simulate the microstructure of magnetic fluids under an external magnetic field. On that basis, a model was established through magnetic dipole theory to delve into the spatial magnetic field distribution of magnetic fluids. The findings reveal that the application of a magnetic field leads to the formation of chain-like structures within the magnetic fluids, resulting in inhomogeneous spatial magnetic field distribution. The size and concentration of MNPs are crucial determinants that significantly affect the microstructure of magnetic fluid and its spatial magnetic field distribution. Furthermore, environmental conditions such as external magnetic field strength or temperature can also regulate the positions of MNPs within magnetic fluids and the spatial magnetic field distribution of the magnetic fluids. These observations enrich the comprehension of the fundamental mechanisms of magnetic fluids and their response to diverse factors, advancing the growing comprehension on the characteristics and applications of these remarkable magnetic fluids.

Improvements of magnetic nanoparticle assays for SARS-CoV-2 detection using a mimic virus approach

Immunoassays with magnetic nanoparticles (MNPs) as markers are a promising approach for the fast and sensitive virus detection. Upon binding of antibody-functionalized MNP on virus proteins, the hydrodynamic diameter increases and a change in the Brownian relaxation time can be measured. In this study, we detect the whole SARS-CoV-2 by mimicking it with streptavidin-coated polystyrene beads with biotinylated spike proteins. Changes of the MNP dynamics are measured by alternating current susceptometry and magnetic particle spectroscopy. Due to the multiple binding sites of MNP and virus, crosslinking enlarges the change of the hydrodynamic diameter. In order to improve the sensitivity and the limit of detection of the assay, the ratio of the virus to the MNP amount RMV/MNP is investigated in detail. High RMV/MNP ratios lead to a saturation of the MNPs with viruses, so that the cluster size and therefore the sensitivity decrease again. Additionally, it is found that the smallest virus concentrations can be detected for small MNP concentrations. It is also shown that the RMV/MNP range that can be used for an unambiguous detection of viruses depends on the virus/MNP concentration; it shifts with increasing MNP concentration to smaller RMV/MNP values. For very small virus concentrations, an increase of the Brownian relaxation time is detected implying a decrease of the hydrodynamic diameter. Furthermore, the optimal antibody concentration for MNP functionalization was determined. It is also found that a washing process with a centrifuge improves the sensitivity by reliably removing unbound antibodies and eliminating small MNPs with improper functionalization.

Electric partial discharges in biodegradable oil-based ferrofluids: A study on effects of magnetic field and nanoparticle concentration

This paper presents an experimental study of partial discharge activity in ferrofluids based on biodegradable transformer oil and iron oxide nanoparticles. Three ferrofluid samples with low, medium and high nanoparticle concentrations are employed in the research. The basic ferrofluid characterization is followed by a partial discharge experiment exposing the ferrofluids to a high voltage in a needle-plate electrode configuration. The analysis confirms that the apparent charge and number of discharges decrease with increasing nanoparticle concentration. These findings are interpreted with reference to the well-recognised electro-hydrodynamic streamer model. The charge trapping by nanoparticles hinders the ionization and discharge development. The study also focuses on the partial discharge activity in the ferrofluids under the action of a static magnetic field acting perpendicularly to the electric field. A decreasing trend in the number of discharges due to the magnetic field is revealed. A qualitative explanation is provided based on the field-induced cluster formation and charge mobility reduction. The presented experiment and the discussed findings may be valuable for practical application of the ferrofluid in high voltage equipment with a special need for partial discharge suppression.