Magnetic Nanoparticles In Solution Research Articles

Evaluation of a Balloon Implant for Simultaneous Magnetic Nanoparticle Hyperthermia and High-Dose-Rate Brachytherapy of Brain Tumor Resection Cavities

Previous work has reported the design of a novel thermobrachytherapy (TBT) balloon implant to deliver magnetic nanoparticle (MNP) hyperthermia and high-dose-rate (HDR) brachytherapy simultaneously after brain tumor resection, thereby maximizing their synergistic effect. This paper presents an evaluation of the robustness of the balloon device, compatibility of its heat and radiation delivery components, as well as thermal and radiation dosimetry of the TBT balloon. TBT balloon devices with 1 and 3 cm diameter were evaluated when placed in an external magnetic field with a maximal strength of 8.1 kA/m at 133 kHz. The MNP solution (nanofluid) in the balloon absorbs energy, thereby generating heat, while an HDR source travels to the center of the balloon via a catheter to deliver the radiation dose. A 3D-printed human skull model was filled with brain-tissue-equivalent gel for in-phantom heating and radiation measurements around four 3 cm balloons. For the in vivo experiments, a 1 cm diameter balloon was surgically implanted in the brains of three living pigs (40–50 kg). The durability and robustness of TBT balloon implants, as well as the compatibility of their heat and radiation delivery components, were demonstrated in laboratory studies. The presence of the nanofluid, magnetic field, and heating up to 77 °C did not affect the radiation dose significantly. Thermal mapping and 2D infrared images demonstrated spherically symmetric heating in phantom as well as in brain tissue. In vivo pig experiments showed the ability to heat well-perfused brain tissue to hyperthermic levels (≥40 °C) at a 5 mm distance from the 60 °C balloon surface.

3,4-Dihydroxiphenylacetic Acid-Based Universal Coating Technique for Magnetic Nanoparticles Stabilization for Biomedical Applications.

Magnetic nanoparticles based on iron oxide attract researchers' attention due to a wide range of possible applications in biomedicine. As synthesized, most of the magnetic nanoparticles do not form the stable colloidal solutions that are required for the evaluation of their interactions with cells or their efficacy on animal models. For further application in biomedicine, magnetic nanoparticles must be further modified with biocompatible coating. Both the size and shape of magnetic nanoparticles and the chemical composition of the coating have an effect on magnetic nanoparticles' interactions with living objects. Thus, a universal method for magnetic nanoparticles' stabilization in water solutions is needed, regardless of how magnetic nanoparticles were initially synthesized. In this paper, we propose the versatile and highly reproducible ligand exchange technique of coating with 3,4-dihydroxiphenylacetic acid (DOPAC), based on the formation of Fe-O bonds with hydroxyl groups of DOPAC leading to the hydrophilization of the magnetic nanoparticles' surfaces following phase transfer from organic solutions to water. The proposed technique allows for obtaining stable water-colloidal solutions of magnetic nanoparticles with sizes from 21 to 307 nm synthesized by thermal decomposition or coprecipitation techniques. Those stabilized by DOPAC nanoparticles were shown to be efficient in the magnetomechanical actuation of DNA duplexes, drug delivery of doxorubicin to cancer cells, and targeted delivery by conjugation with antibodies. Moreover, the diversity of possible biomedical applications of the resulting nanoparticles was presented. This finding is important in terms of nanoparticle design for various biomedical applications and will reduce nanomedicines manufacturing time, along with difficulties related to comparative studies of magnetic nanoparticles with different magnetic core characteristics.

PEROXIDASE-LIKE ACTIVITY OF MAGNETIC NANOPARTICLES IN THE PRESENCE OF BLOOD PROTEINS

The generation of hydroxyl radicals from hydrogen peroxide in aqueous solutions containing magnetic nanoparticles (MNPs), hemoglobin (Hb), immunoglobulin G (IgG), and human serum albumin (HSA) has been determined. The dependence of the rate of formation of the oxidized product of o-phenylenediamine (o-PDA) on the concentration of MNPs in solution, as well as on the concentration of proteins, was obtained. The peroxidase-like activity of MNPs was shown to decrease in the presence of HSA and IgG, while the addition of Hb to the reaction mixture was leading to its decrease and increase depending on protein concentration. The obtained effects can be used in the development of systems based on MNPs for theranostics, in particular, for suppression of tumor growth, and in predicting the ability of particles to catalyze the generation of reactive oxygen species (ROS) in vivo.

Development of Positively Charged Poly-L-Lysine Magnetic Nanoparticles as Potential MRI Contrast Agent.

A colloidal solution of magnetic nanoparticles (MNPs) modified with biocompatible positively charged poly-L-lysine (PLL) with an oleate (OL) layer employed as an initial coating was produced as a potential MRI contrast agent. The effect of various PLL/MNPs' mass ratios on the samples' hydrodynamic diameter, zeta potential, and isoelectric point (IEP) was studied by the dynamic light-scattering method. The optimal mass ratio for MNPs' surface coating was 0.5 (sample PLL0.5-OL-MNPs). The average hydrodynamic particle size in the sample of PLL0.5-OL-MNPs was 124.4 ± 1.4 nm, and in the PLL-unmodified nanoparticles, it was 60.9 ± 0.2 nm, indicating that the OL-MNPs' surface became covered by PLL. Next, the typical characteristics of the superparamagnetic behavior were observed in all samples. In addition, the decrease in saturation magnetizations from 66.9 Am2/kg for MNPs to 35.9 and 31.6 Am2/kg for sample OL-MNPs and PLL0.5-OL-MNPs also confirmed successful PLL adsorption. Moreover, we show that both OL-MNPs and PLL0.5-OL-MNPs exhibit excellent MRI relaxivity properties and a very high r2(*)/r1 ratio, which is very desirable in biomedical applications with required MRI contrast enhancement. The PLL coating itself appears to be the crucial factor in enhancing the relaxivity of MNPs in MRI relaxometry.

Magnetic relaxation switch sensor based on aptamer-modified poly-L-lysine-ferroferric oxide magnetic nanoparticles and graphene oxide for the determination of insecticides in vegetables.

A simple and effective graphene oxide-magnetic relaxation switch (GO-MRS) sensor that combines graphene oxide (GO) and aptamer-modified poly-L-lysine(PLL)-Fe3O4 nanoparticles (Fe3O4@PLL-Apt NPs) was designed for the detection of acetamiprid (ACE). In this sensor, Fe3O4@PLL-Apt NPs acted as a relaxation signal probe and GO facilitated the generation of relaxation signal changes (dispersion/aggregation shift), while the aptamer is a molecular component that recognizes ACE. This GO-assisted magnetic signal probe improves the stability of magnetic nanoparticles in solution and enhances their sensitivity to small molecules while avoiding cross-reactions. Under optimal conditions, the sensor exhibits a wide working range (10-80nM) and low detection limit (8.43nM). The spiked recoveries ranged from 96.54 to 103.17%, with a relative standard deviation (RSD) of less than 2.3%. In addition, the performance of the GO-MRS sensor matched that of the standard method (liquid chromatography-mass spectrometry (LC-MS)), indicating that the GO-MRS sensor is suitable for the detection of ACE in vegetables.

Characterization of dextran-coated magnetic nanoparticles (Fe3O4) conjugated with monoclonal antibody through low gradient magnet and centrifugation-based buffer separation processes

Conjugation of magnetic nanoparticles (MNPs) with biomolecules can be achieved through covalent or non-covalent bonding and chemisorption. By glutaraldehyde cross-linking, we successfully conjugated mouse monoclonal antibody (Ab) with amine-functionalized dextran-coated MNPs of diameter 50 nm. We aim to characterize the antibody-conjugated MNPs (Ab-MNPs) after buffer separation through low-gradient magnet and centrifugation. The magnetic separation/washing was achieved throughout the conjugation process by attaching the MNPs solution to a natural magnet for about 12 h. The centrifugation-based separation steps were done at 15,000×g for 30 min. The transmission electron microscope (TEM) data showed the flower-shaped core MNPs and their increased diameter after conjugation with Abs. The nanoparticle tracking analysis (NTA) also revealed the size distribution and drift velocities in MNPs and Ab-MNPs. The size distribution and concentration data showed an increased size and a lower value after conjugation, respectively. The drift velocities of Ab-MNPs prepared by the centrifugation method were significantly reduced than magnetic separation and standard MNPs.

Fe<sub>3</sub>O<sub>4</sub> Nanoparticles Prepared by Coprecipitations Method for Hyperthermia Therapy

Magnetic nanoparticles (Fe3O4) have considerable attention in various biomedical applications such as biosensors, drug delivery systems in the body, magnetic resonance imaging (MRI), and hyperthermia therapy. Hyperthermia therapy uses heat controlled by applied AC (Alternating Current) magnetic to kill cancer cells. This research aims to determine the effect of changes in temperature caused by the AC magnetic field on the varied magnetic nanoparticle solution. The Synthesize of Fe3O4 used the coprecipitation method to produce Fe3O4 nanoparticles. Mass of Fe3O4 nanoparticles varied of 95 mg and 125 mg. Nanoparticles physical properties were characterized using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), and vibrating sample magnetometer (VSM). XRD profiles indicated that magnetic (Fe3O4) nanoparticles were successfully synthesized with a crystal size of 7.76 nm. SEM characterization of Fe3O4 nanoparticles was carried out at a magnification of 150.000 times and the average diameter of Fe3O4 powder nanoparticles was 20 nm. The temperature change measurement was performed using an AC magnetic field of 2.8 mT and frequency of 343 Hz, and time recorded changes temperature in 660 seconds. The temperature changes for solution concentrations of 95 mg and 125 mg were 7.7°C and 9.8°C, respectively. the concentration of solutions affects the value of the Specific Absorption Rate (SAR). The SAR values of each concentration of Fe3O4 solution were 0,0069 W/g and 0.0096 W/g. It proves that Fe3O3 prepared by coprecipitation method has potential for hyperthermia therapy application.

PHSOR03 Presentation Time: 12:40 PM: Radiation Dosimetry of a Dual-Modality Balloon Implant for Simultaneous HDR Brachytherapy and Magnetic Nanoparticle Hyperthermia to Treat Brain Tumor Resection Cavities

<h3>Purpose</h3> Glioblastoma multiforme (GBM) is an aggressive brain tumor that generally recurs locally and has a dismal median survival of less than 18 months<i>. In vivo</i> studies have shown that simultaneous hyperthermia and radiation can enhance the radiation response by a factor of up to 5. Our group developed a novel dual-modality thermobrachytherapy (TBT) balloon device to accomplish this goal. The balloon will combine magnetic fluid hyperthermia and HDR brachytherapy, which will be delivered right after brain tumor resection, so that the at-risk tissue adjacent to the tumor resection cavity will conform to the balloon shape and receive uniform radiation and thermal dose. This abstract focuses on the possible effects of hyperthermia on radiation dosimetry as well as the effects of balloon shape. <h3>Methods</h3> The current version of our TBT balloon device consists of a balloon filled with magnetic nanoparticle solution (nanofluid) and a flexible sheath with three ports to insert the HDR catheter and fiber-optic thermal probe and inject the nanofluid. We tested the balloon in air and activated the nanofluid using an external magnetic field induced by a 133 kHz induction coil. Two balloon designs were tested: a spherical one with 4 cm diameter, and a teardrop-shaped balloon with an axial diameter of 3 cm and measuring 3.7 cm along the shaft. We used Gafchromic film and RIT imaging software to analyze the in-air dose distribution of an HDR source dwell in both types of balloons, filled with distilled water and then nanofluid, as well as without and with simultaneous hyperthermia, where the coil power was escalated until reaching intra-balloon temperatures greater than 55°C. Experimental setup and radiation dose profiles can be found in Figure 1. <h3>Results</h3> The presence of the nanofluid, magnetic field and heat up to 66°C did not affect radiation dose distribution significantly in the spherical balloon (less than 10% difference). However, the teardrop-shaped balloon dose profiles showed a notable difference (about 20%) in dose magnitude with the presence of nanofluid and/or heat. Nonetheless dose distributions looked symmetrical in all cases. <h3>Conclusions</h3> The current device design is still in progress, but this study illustrated that a spherical balloon shape may be preferential for simultaneous hyperthermia and HDR brachytherapy. Furthermore, this radiation dosimetry study demonstrated compatibility and robustness of the prototype balloon components and desirable symmetrical dose distribution.

Low-gradient magnetic separation of magnetic nanoparticles under continuous flow: Experimental study, transport mechanism and mathematical modelling.

Low-gradient magnetic separation (LGMS) of magnetic nanoparticles (MNPs) has been proven as one of the techniques with great potential for biomedical and environmental applications. Recently, the underlying principle of particle capture by LGMS, through a process known as magnetophoresis, under the influence of hydrodynamic effect has been widely studied and illustrated. Even though the hydrodynamic effect is very substantial for batch processes, its impact on LGMS operated at continuous flow (CF) condition remained largely unknown. Hence, in this study, the dynamical behaviour of LGMS process operated under CF was being studied. First, the LGMS experiments using poly(sodium 4-styrenesulfonate)-functionalized-MNP as modelled particle system were performed through batchwise (BW) and CF modes at different operating conditions. Here BW operation was used as a comparative study to elucidate the transport mechanism of MNP under the similar environment of CF-LGMS process, and it was found out that the convection induced by magnetophoresis (timescale effective is ∼1200s) is only significant at far-from-magnet region. Hence, it can be deduced that forced convection is more dominant on influencing the transport behaviour of CF-LGMS (with resident time ≤240s). Moreover, we found that the separation efficiency of CF-LGMS process can be boosted by the higher number of magnets, the higher MNP concentration and the lower flowrate of MNP solution. To better illustrate the underlying dynamical behaviour of LGMS process, a mathematical model was developed to predict its kinetic profile and separation efficiency (with average error of ∼2.6% compared to the experimental results).

Catalytic activity of magnetite and its magnetic heating properties

Magnetite (Fe3O4) nanoparticles have been successfully synthesized using cetyltrimethylammonium bromide (CTAB). The stabilizing agent CTAB reduces agglomeration of magnetic nanoparticles in solution. The formation of Fe3O4 nanoparticles was confirmed by X-ray diffractometry, IR spectroscopy and Mössbauer spectroscopy. The average crystallite size of magnetite nanoparticles was found to be 14.41 nm. The catalytic activity of the obtained magnetite have been tested in a batch reactor. Due to favourable redox properties and low crystallite size, magnetite nanoparticles have high catalytic activity in the decomposition of H2O2. The degree of H2O2 decomposition was 77.41% in 120 min. The induction heating of synthesized Fe3O4 nanoparticles have been investigated. At magnetite concentration of 40 mg/ml, the specific absorption rate is equal 14.57 W/g.

Capture efficiency of magnetic nanoparticles through the compaction effect of a microparticles column.

When a magnetic nanoparticle solution flows through a porous medium formed by iron microparticles packed in a microfluidic channel, the nanoparticles get trapped within the column in the presence of a magnet. A complex interplay between magnetic and fluid forces within the magnetized porous medium governs the trapping of nanoparticles. However, how does the packing state of the microparticles affect the trapping of nanoparticles? Will more nanoparticles be trapped on a loose or a tight packing? In this work, we present experiments that show that the capture of nanoparticles is determined by the total volume occupied by the column, independent of its packing density. We present a simple analytical model based on the competition of drag and magnetic forces that shows that our system can be useful to develop and test more complete and accurate models. We also developed a technique to measure the columns' minute mass and its packing density, which consists of injecting polydimethylsiloxane into the acrylic microfluidic device. Our work can help with the optimization of environmental and biomedical applications based on high-gradient magnetic nanoparticle separation.

Enzymatic Delivery of Magnetic Nanoparticles into Mitochondria of Live Cells.

Delivering magnetic nanoparticles (MNPs) into mitochondria provide a facile approach to manipulate cell life because mitochondria play essential roles in cell survival and death. Here we report the use of enzyme-responsive peptide assemblies to deliver MNPs into mitochondria of live cells. The mitochondria-targeting peptide (Mito-Flag), as the substrate of enterokinase (ENTK), assembles with MNPs in solution. The MNPs that are encapsulated by Mito-Flag peptides selectively accumulate to the mitochondria of cancer cells, rather than normal cells. The mitochondrial localization of MNPs reduces the viability of the cancer cells, but hardly affects the survival of the normal cell. This work demonstrates a new and facile strategy to specifically transport MNPs to the mitochondria in cancer cells for exploring the applications of MNPs as the targeted drug for biomedicine and cancer therapy.

Laser Synthesis of Magnetic Nanoparticles in Liquids and Application in the Fabrication of Polymer–Nanoparticle Composites

The method of synthesis of nanoparticles in solution by laser ablation of a bulk target material immersed in a liquid does not require the use of any reducible chemical precursors or colloidal stabilizing agents. The resulting colloids are ultrapure, and in certain cases, the synthesized nanoparticles are surface-ligand-free (have “bare” surfaces). Furthermore, laser irradiation of micro/nanomaterials suspended in a liquid can lead to the synthesis of nanoparticles in solution with unique physicochemical properties. Interest in the application of the method for the synthesis of magnetic nanoparticles usually originates from the following facts: (i) Magnetic oxide or carbide nanoparticles can be directly synthesized by laser ablating the corresponding elemental target material in the appropriate liquid, (ii) magnetoplasmonic bimetallic alloy nanoparticles (e.g., FeAu), even composed of elements that are immiscible at any temperature in the solid or liquid phase (e.g., FeAg, CoAg), can be synthesized by ablating nonalloyed bimetallic targets, (iii) under the application of an external magnetic field, nanoparticle chains and strands can be fabricated that are characterized by a high packing density of the nanoparticles that together with their “bare” surfaces result in the strands having both a high aspect ratio and electrical conductivity, (iv) magnetic nanostructures that consist of nanoparticles and nanomaterials with different morphologies or properties can be fabricated, and (v) nanoparticles of intrinsically nonmagnetic oxides exhibiting the so-called d0 ferromagnetism can be synthesized. By using laser-synthesized-in-liquid magnetic nanoparticles in the fabrication of polymer–nanoparticle composites (magnetic nanocomposites), the presence of any chemical reaction byproducts in the nanocomposite is avoided. The nanoparticles form direct chemical bonds with the polymer matrix. Nanoparticle strands formed in the nanocomposite provide it with a high electrical conductivity while preserving its optical transparency. This Review is focused on the synthesis of magnetic nanoparticles in solution by laser ablation of a bulk target material immersed in a liquid or laser irradiation of micro/nanoparticles or micro/nanomaterials suspended in a liquid and the fabrication of magnetic nanocomposites using these nanoparticles.

Development of an in-line magnetometer for flow chemistry and its demonstration for magnetic nanoparticle synthesis.

Despite the wide usage of magnetic nanoparticles, it remains challenging to synthesise particles with properties that exploit each application's full potential. Time consuming experimental procedures and particle analysis hinder process development, which is commonly constrained to a handful of experiments without considering particle formation kinetics, reproducibility and scalability. Flow reactors are known for their potential of large-scale production and high-throughput screening of process parameters. These advantages, however, have not been utilised for magnetic nanoparticle synthesis where particle characterisation is performed, with a few exceptions, post-synthesis. To overcome this bottleneck, we developed a highly sensitive magnetometer for flow reactors to characterise magnetic nanoparticles in solution in-line and in real-time using alternating current susceptometry. This flow magnetometer enriches the flow-chemistry toolbox by facilitating continuous quality control and high-throughput screening of magnetic nanoparticle syntheses. The sensitivity required to monitor magnetic nanoparticle syntheses at the typically low concentrations (<100 mM of Fe) was achieved by comparing the signals induced in the sample and reference cell, each of which contained near-identical pairs of induction and pick-up coils. The reference cell was filled only with air, whereas the sample cell was a flow cell allowing sample solution to pass through. Balancing the flow and reference cell impedance with a newly developed electronic circuit was pivotal for the magnetometer's sensitivity. To showcase its potential, the flow magnetometer was used to monitor two iron oxide nanoparticle syntheses with well-known particle formation kinetics, i.e., co-precipitation syntheses with sodium carbonate and sodium hydroxide as base, which have been previously studied via synchrotron X-ray diffraction. The flow magnetometer facilitated batch (on-line) and flow (in-line) synthesis monitoring, providing new insights into the particle formation kinetics as well as, effect of temperature and pH. The compact lab-scale flow device presented here, opens up new possibilities for magnetic nanoparticle synthesis and manufacturing, including 1) early stage reaction characterisation 2) process monitoring and control and 3) high-throughput screening in combination with flow reactors.

Imaging of Magnetic Nanoparticles Using Small TMR Sensor With an Excitation-Compensation Scheme

Magnetic nanoparticle imaging (MPI) is an emerging non-invasive technique with potential applications in bio-medical diagnostic and material science. In this paper, we propose a new method for MPI using tunnel magnetoresistance (TMR) sensor with an area of dimensions 0.45 mm*0.45 mm. The small size of the sensor promotes high level of integration and fine spatial resolution for magnetic field measurements. A solenoid excitation coil carrying alternating current is used to magnetize the magnetic nanoparticles (MNPs). We used commercial MNPs solution named synomag ®-D with iron concentration 10 mg/ml as sample. The response of the MNPs is measured by the TMR sensor during a 2D raster scan resulting in a magnetic image. In order to eliminate the negative effect of the strong background field from the excitation coil, a compensation coil which is located close to the TMR sensor is utilized to subtract the background signal in situ during measurements. Comparing the experimental results with and without the compensation scheme shows that the setup with the compensation coil cancels 95% of the background signal and increases the signal to noise ratio (SNR) from 7 dB to 10 dB. Mainly considering the tradeoff of 1/${f}$ noise and the MNPs response to the excitation frequency, the operating frequencies of 135 Hz, 235 Hz and 335 Hz were investigated in this study. Experimental results show that the system is capable of imaging $5~\mu \text{L}$ MNPs solution with a 5 mm lift-off from the sensor to the top surface of the MNPs sample. Furthermore, an `L' shape formed by 6 holes with $1~\mu \text{L}$ MNPs solution in each is imaged by the system. In comparison, it is very challenging for conventional MPI with coils as pickup sensors to image $10~\mu \text{g}$ irons in $1~\mu \text{L}$ MNPs solution at the low operating frequency. This is because TMR sensor has much better sensitivity than coils in the low frequency range. This work demonstrates the feasibility of using small TMR sensor with an excitation-compensation scheme for MPI. The advantages of high sensitivity, fine spatial resolution and low cost of the probe make it a promising alternative for future bio-medical research to measure the 3-D location and concentration of magnetic nanoparticles.

Thermal tissue damage analysis for magnetothermal neuromodulation and lesion size minimization

The study of temperature profiles within the central nervous system (CNS) when exposed to an alternating magnetic field (AMF) as a plausible therapy for neuropsychiatric disorders is crucial. This new procedure can be a better alternative for conventional permanent implanted electrodes treatment for CNS diseases such as Parkinson's disease (PD). Hyperthermic treatments are highly dependent on biomaterial thermophysical properties, magnetic nanoparticle (MNP) solution and magnetic field characteristics. This manuscript aims to ascertain the optimum conditions for magnetothermal neuromodulation. Hence, we employ a comprehensive modeling and utilize finite element method (FEM) for simulations to obtain the temperature distribution across the exposed tissue by which the lesion size is evaluated. The results are compared against experimental data in the literature. Local temperature distribution demonstrates an elevated temperature of 57 °C particularly, at the center of the injected solution after exposure. It is shown that a high fraction of the tissue around the injected magnetic nanoparticle solution is damaged mainly due to crossing the safe temperature domain (43 °C < Ttissue < 50 °C). In this investigation, we advance an optimized approach to a theoretical model of neuromodulation, based on Pennes’ equation, that includes a novel stimulation constraint. We establish several new results with this technique; in particular, we demonstrate: the method can be utilized to compute optimized parameter values. Consequently, the minimum necessary activation temperature for magnetothermal stimulation is achieved. Meanwhile, the underlying biomaterial is maintained at low levels of thermal-induced damage. Statement of SignificanceThe invasiveness of conventional therapy for neurodegenerative diseases has prompted neuroscientists to discover a new treatment with the least side effects. Magnetothermal stimulation as a great potential alternative, utilizes nano-transducers to convert magnetic field energy to heat and activate targeted neurons. This technique has exhibited promising test results that ameliorates the symptoms. This manuscript by employing an optimization method and damage analysis, establishes the methodology to diminish the adverse impacts of magnetothermal stimulation. The optimum stimulation was established which satisfies the neuron activation requirement while causing the least damage on the targeted brain tissue.

Broadband optical measurement of AC magnetic susceptibility of magnetite nanoparticles

Characterization of magnetic nanoparticles in solution is challenging due to the interplay between magnetic relaxation and agglomeration. The AC magnetic susceptibility of magnetite nanoparticles in water has been studied using magneto-optical methods in the frequency range of 10 Hz–250 kHz. The Faraday effect is detected simultaneously with changes in the fluid configuration. It is shown that the relative sensitivity to the magnetic and structural response can be adjusted by varying the wavelength, paving the way toward spatially resolved studies at the micro-scale.

Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction**Project supported by the National Natural Science Foundation of China (Grant Nos. 11934009, 11974187, and 11604156).

Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles (MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses (2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction (MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.

Laser monitoring of dynamic behavior of magnetic nanoparticles in magnetic field gradient

Manipulation of magnetic nanoparticles (MNP) by an external magnetic field has been widely studied in the fields of biotechnology and medicine for collecting and/or reacting biomaterials in the solutions. Here, dynamic behaviors of MNP in solution under changing gradient magnetic field were investigated using our newly developed laser transmission system (LTS) with a variable magnetic field manipulator. The manipulator consists of a moving permanent magnet placed beside the optical cell filled with MNP solution. A laser beam was focused on the cell and the transmitted laser beam was detected by a silicon photodiode, so that the localized concentration of the MNP at the focused area could be evaluated by the intensity of transmitted laser beam. In this study, the LTS was applied to evaluate dynamic behaviors of MNP in serum solution. Dispersion and aggregation of MNP in the solution were evaluated. While time evolution of dispersion depends on the serum concentration, the behavior during aggregation by the magnetic field was independent of the serum concentration. A series of measurements for zeta-potentials, distributions of particle size, and magnetization distributions was carried out to understand this difference in the behavior. The results indicated that a Brownian motion was main force to distribute the MNP in the solution; on the other hand, the magnetic force to the MNP mainly affected the behavior during aggregation of the MNP in the solution.

Reversible rearrangement of magnetic nanoparticles in solution studied using time-resolved SAXS method.

Superparamagnetic nanoparticles have broad applications in biology and medicines. Quantitative measurements of magnetic beads in solution are essential in gaining comprehensive understanding of their dynamics and developing applications. Here, using synchrotron X-ray sources combined with well controlled magnetic fields, the results from small-angle X-ray scattering (SAXS) experiments on superparamagnetic particles in solution under the influence of external magnetic fields are reported. The particles mostly remain in monodispersed states and the linear aggregates tend to be aligned with the external magnetic field. After removing the magnetic fields, the superparamagnetic nanoparticles quickly recover to their original states indicating high reversibility of the rearrangement under the control of a magnetic field. The external magnetic field instrument composed of paired permanent magnets is integrated into the SAXS beamline at the Shanghai Synchrotron Radiation Facility providing a platform for studying time-resolved dynamics induced by magnetic fields.