Aggregation Of Magnetic Nanoparticles Research Articles

Effect of flowrate on the size segregation of magnetic nanoparticles by using continuous flow magnetic separator

Magnetic Nanoparticles (MNPs) possess significant potential across various sectors due to their versatility. However, specific MNP sizes are crucial for effective utilization. Traditional methods for synthesizing monodispersed MNPs are often expensive, complex, or environmentally harmful. This study proposes the effect of flow rate on the size segregation of MNPs using a continuous flow low gradient magnetic separator (CFLGMS). To produce MNPs that are monodispersed, firstly, MNPs undergo functionalization with the polyelectrolyte, poly (sodium 4-styrene sulfonate) (PSS), to enhance colloidal stability. Employing PSS molecules as splicing agents effectively inhibits MNP aggregation. To further enhance the monodispersity of MNPs, continuous flow is facilitated by configuring three separator columns in series, with permanent magnets (NdFeB) attached to the sides. As larger MNPs exhibit stronger magnetic field attraction, resulting in their capture by magnets first, followed by smaller MNPs, and finally the smallest ones. Consequently, MNPs captured in Column 1 possess the largest size, while those in Column 3 have the smallest size. Additionally, this paper investigates the impact of solution flowrate on size segregation efficiency. By varying the solution flow rate (10 mL/min, 15 mL/min, and 20 mL/min), it is found that the performance of the size segregation system is higher under the lower solution flowrate.

Aggregates of magnetic nanoparticles with fractal-like structure: nucleation and magnetic response

Aggregates of magnetic nanoparticles with fractal-like structure: nucleation and magnetic response

Magnetic Nanoparticle Aggregation and Complete De-encapsulation of Such Aggregates from a Liquid Drop Interior.

Magnetic nanoparticles (MNPs) have been extensively used for drug delivery, on-demand material deposition, etc. In this study, we demonstrate the capability to extract such MNPs on-demand from a magnetic nanoparticle-laden drop (MNLD) (i.e., a drop of a stable aqueous dispersion of MNPs), suspended inside a highly viscous polymer (poly(dimethylsiloxane) or PDMS) medium in the presence of an externally applied magnetic field. The phenomena involve the aggregation of the MNPs inside the drop and the consequent extraction of the MNP aggregate out of the drop, with the drop retaining its original shape after the MNP aggregate extraction. We define this latter phenomenon as de-encapsulation. This is the first study that, to the best of our knowledge, demonstrates such precise, controlled, and on-demand removal of the NPs from the interior of a drop (where the NPs, which were originally inside the drop, breach the drop interface and get completely separated from the drop as an aggregate) without any permanent deformation of the drop. We quantify the effect of the changes in the MNP concentration and the drop volume in determining the de-encapsulation distance, which refers to the distance between the drop and the location of the magnet at the time instant when the MNP aggregate leaves the drop. We further identify the volume of the aggregates extracted from the drop and the mechanisms causing such de-encapsulation. We propose a theory to describe the process, and our theoretical predictions capture the experimental trends well. In addition, we also demonstrate multiple, back-to-back MNP aggregate extractions from a single MNLD at different sites, indicating the possibility that the MNLD can be used as an on-demand carrier and depositor of materials. Overall, our results, in addition to demonstrating the first-of-its-kind de-encapsulation of NPs (in the form of an aggregate) from the drop interior, demonstrate a method to control the dynamics, extraction, and targeted deposition of the MNPs.

Magnetic-field-controllable elasticity of helical spring magnets composed of magnetic-particle-polymer composites

Abstract We experimentally demonstrated the ability to control the spring constant of helical mechanical springs using a magnetic field. These springs were composed of magnetic nanoparticles embedded within an elastic polymer matrix. The composite material, in its gel form, was injected into a 3D-printed mold featuring a helical-spring-shaped cavity. An external magnetic field applied perpendicular to the coil axis of the spring allows the aligmment of the magnetic nanoparticle assemblies (chain axis) in the field direction. This alignment process determines the preferred magnetization orientation of the particle assembly chain, thereby balancing the magnetic force between the magnetic anisotropy field and the Zeeman field under a given external field. When the spring is subjected to compression or stretching loads under an externally applied magnetic field, these two magnetic fields modify the effective spring constant of the magnetic helical spring by ~ 31 %, incresing it from 8.7 N/m (under no field) to 11.5 N/m at 300 mT. Analytical modeling using a simplified rod geometry aptly explains the experimental results, demonstrating that the spring constant linearly increases with the field strength up to 300 mT. Such composite magnetic helical springs could be utilized as active vibration absorbers or isolators due to their field-controllable elasticity.

Heat Generation and Diffusion in an Assembly of Magnetic Nanoparticles: Application to Magnetic Hyperthermia

We investigate the thermal generation and transport properties of an assembly of magnetic nanoparticles embedded in a solid or fluid matrix, subjected to an AC magnetic field. For this purpose, we first build the heat equation for the assembly using the effective thermal transport coefficients obtained within the effective medium approach. In the present calculation, the SAR is obtained from the (linear) dynamic response of the assembly to the AC magnetic field. We numerically solve the extended heat equation and, as a preliminary study, we obtain the space-time profile of the temperature and total power absorbed by the system.

Photothermal conversion of CO2 with high activity and stability over Ni-based composite nanochains

Solar-driven CO2 conversion to valuable products is a promising way to realize a carbon-neutral economy. Great progress has been made on photothermal catalysts with high selectivity and activity, but improved materials via a more efficient and cost-effective synthetic strategy are needed. Herein, we present a one-pot synthetic strategy of nickel/metal oxide nanostructured chains for the photothermal conversion of CO2 into methane. Nickel ions were in-situ reduced in a growth solution in the presence of alumina nanocrystals, where the formation and assembly of magnetic nickel nanoparticles decorated with Al2O3 nanocrystals simultaneously proceeded. The obtained composite nanochains exhibited a stable production rate of CH4 as high as 128 mmol·gcat−1·h−1 with ∼ 99% selectivity in continuous cycling test. The structure analysis of the Ni/Al2O3 composite indicates that a small amount of Al2O3 nanocrystals introduced in the nanocomposites not only ensures sufficient active site exposure to reactive molecules but also prevents the nickel nanoparticles from drastically sintering at high temperatures. The flexibility of this rapid synthesis strategy is also verified by using titania for the synthesis of Ni/TiO2 nanocatalysts, and stable catalytic performance has been achieved, suggesting its potential for practical solar-driven CO2 hydrogenation to valuable fuels.

Dynamically reconfigurable complex liquid crystal emulsions

ABSTRACT Complex emulsions, containing liquid crystals (LCs) and immiscible oils such as fluorocarbon or silicone oils, present innovative functionalities in soft materials. These emulsions exhibit dynamic reconfiguration in droplet morphology and internal LC organisation, expanding applications in optics, sensing, and active matter. This review highlights the evolution and potential of LC-containing complex emulsions. Emphasis is placed on emulsions featuring dynamic and reversible morphological transformations and LC reorganisation, underpinning their suitability for tunable micro-lenses, chemical sensing, and biosensing. Nematic LCs within complex emulsions allow for topological defect-driven functionalization, attaching antibodies to induce substantial changes in the LC director field upon interfacial recognition events. This feature may facilitate the development of ultrasensitive chemical and biological sensors. Moreover, cholesteric LCs, through their selective reflection, enable the rapid and sensitive detection of foodborne pathogens. The controlled assembly of magnetic nanoparticles at interfaces illustrates advancements towards magnetic field-responsive and active colloids. Future perspectives include exploiting these properties for intelligent colloidal systems capable of autonomous behaviour, and furthering applications in dynamic photonic devices, high-security identification tags, and responsive lens systems.

Experimental Thermal Conductivity Studies of Agar-Based Aqueous Suspensions with Lignin Magnetic Nanocomposites

Nanoparticle additives increase the thermal conductivity of conventional heat transfer fluids at low concentrations, which leads to improved heat transfer fluids and processes. This study investigates lignin-coated magnetic nanocomposites (lignin@Fe3O4) as a novel bio-based magnetic nanoparticle additive to enhance the thermal conductivity of aqueous-based fluids. Kraft lignin was used to encapsulate the Fe3O4 nanoparticles to prevent agglomeration and oxidation of the magnetic nanoparticles. Lignin@Fe3O4 nanoparticles were prepared using a pH-driven co-precipitation method with a 3:1 lignin to magnetite ratio and characterized by X-ray diffraction, FT-IR, thermogravimetric analysis, and transmission electron microscopy. The magnetic properties were characterized using a vibrating sample magnetometer. Once fully characterized, lignin@Fe3O4 nanoparticles were dispersed in aqueous 0.1% w/v agar–water solutions at five different concentrations, from 0.001% w/v to 0.005% w/v. Thermal conductivity measurements were performed using the transient line heat source method at various temperatures. A maximum enhancement of 10% in thermal conductivity was achieved after adding 0.005% w/v lignin@Fe3O4 to the agar-based aqueous suspension at 45 °C. At room temperature (25 °C), the thermal conductivity of lignin@Fe3O4 and uncoated Fe3O4 agar-based suspensions was characterized at varying magnetic fields from 0 to 0.04 T, which were generated using a permanent magnet. For this analysis, the thermal conductivity of lignin magnetic nanosuspensions initially increased, showing a 5% maximum peak increase after applying a 0.02 T magnetic field, followed by a decreasing thermal conductivity at higher magnetic fields up to 0.04 T. This result is attributed to induced magnetic nanoparticle aggregation under external applied magnetic fields. Overall, this work demonstrates that lignin-coated Fe3O4 nanosuspension at low concentrations slightly increases the thermal conductivity of agar aqueous-based solutions, using a simple permanent magnet at room temperature or by adjusting temperature without any externally applied magnetic field.

One-dimensional assemblies of magnetic iron-oxide nanoparticles

Abstract Although high-aspect-ratio iron-oxide nanoparticles (IONPs) are known to have higher heating efficiency than spherical and cubic IONPs and focused in cancer treatment areas, their synthesis methods require high temperatures, vacuum, reduction conditions, and substantial time. In this study, we proposed and established a facile manufacturing method for one-dimensional assemblies of IONPs, expected to increase heating efficiency similar to high-aspect-ratio IONPs. We investigated how the fabrication conditions affect the length of the assemblies and found that the average length of the one-dimensional assemblies increased with the extension of magnetic-field-application time. This result demonstrates that the length could be controlled by adjusting the duration of the magnetic field application.

Magnetic nanoparticles and possible synergies with cold atmospheric plasma for cancer treatment.

The biomedical applications of magnetic nanoparticles (MNPs) have gained increasing attention due to their unique biological, chemical, and magnetic properties such as biocompatibility, chemical stability, and high magnetic susceptibility. However, several critical issues still remain that have significantly halted the clinical translation of these nanomaterials such as the relatively low therapeutic efficacy, hyperthermia resistance, and biosafety concerns. To identify innovative approaches possibly creating synergies with MNPs to resolve or mitigate these problems, we delineated the anti-cancer properties of MNPs and their existing onco-therapeutic portfolios, based on which we proposed cold atmospheric plasma (CAP) to be a possible synergizer of MNPs by enhancing free radical generation, reducing hyperthermia resistance, preventing MNP aggregation, and functioning as an innovative magnetic and light source for magnetothermal- and photo-therapies. Our insights on the possible facilitating role of CAP in translating MNPs for biomedical use may inspire fresh research directions that, once actualized, gain mutual benefits from both.

Ferromagnetic Enhancement of Microcrystalline Cellulose via Chemical Reduction Method

Iron oxide nanoparticles (NPs) have potential in biological, biomedical, and environmental applications because of their magnetic susceptibility, stability, and biocompatibility characteristics. However, it also has limitations, such as the aggregation of magnetic NP. Thus, the outer surface of the particles should be modified by coating materials. This paper focused on synthesizing iron oxide by chemical reduction method and coating it with Fe(III) nitrate, PVP, and hydrazine. The coating solution at two different concentrations was prepared to determine effective and economical usage conditions. The effect of coating iron oxide with microcrystalline cellulose (MCC) was conducted at different concentrations of iron oxide on the nanomaterials with respect to morphological, thermal, and magnetic susceptibility. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated good morphology images of FeNp-MCC. Energy dispersive X-ray (EDX) spectra reveal the presence of carbon, oxygen, and iron in the synthesized microparticles.TGA analysis showed iron material was succesfully formed into the surface of microcrystalline cellulose. Lastly,the magnetism results proved that cellulose is strongly interacting with magnetite nanoparticles.

AND-Logic Cascade Rolling Circle Amplification for Optomagnetic Detection of Dual Target SARS-CoV-2 Sequences.

DNA logic operations are accurate and specific molecular strategies that are appreciated in target multiplexing and intelligent diagnostics. However, most of the reported DNA logic operation-based assays lack amplifiers prior to logic operation, resulting in detection limits at the subpicomolar to nanomolar level. Herein, a homogeneous and isothermal AND-logic cascade amplification strategy is demonstrated for optomagnetic biosensing of two different DNA inputs corresponding to a variant of concern sequence (containing spike L452R) and a highly conserved sequence from SARS-CoV-2. With an "amplifiers-before-operator" configuration, two input sequences are recognized by different padlock probes for amplification reactions, which generate amplicons used, respectively, as primers and templates for secondary amplification, achieving the AND-logic operation. Cascade amplification products can hybridize with detection probes grafted onto magnetic nanoparticles (MNPs), leading to hydrodynamic size increases and/or aggregation of MNPs. Real-time optomagnetic MNP analysis offers a detection limit of 8.6 fM with a dynamic detection range spanning more than 3 orders of magnitude. The accuracy, stability, and specificity of the system are validated by testing samples containing serum, salmon sperm, a single-nucleotide variant, and biases of the inputs. Clinical samples are tested with both quantitative reverse transcription-PCR and our approach, showing highly consistent measurement results.

On-Particle Hyperbranched Rolling Circle Amplification-Scaffolded Magnetic Nanoactuator Assembly for Ferromagnetic Resonance Detection of MicroRNA.

Inspired by natural molecular machines, scientists are devoted to designing nanomachines that can navigate in aqueous solutions, sense their microenvironment, actuate, and respond. Among different strategies, magnetically driven nanoactuators can easily be operated remotely in liquids and thus are valuable in biosensing. Here we report a magnetic nanoactuator swarm with rotating-magnetic-field-controlled conformational changes for reaction acceleration and target quantification. By grafting nucleic acid amplification primers, magnetic nanoparticle (MNP) actuators can assemble and be fixed with a flexible DNA scaffold generated by surface-localized hyperbranched rolling circle amplification in response to the presence of a target microRNA, osa-miR156. Net magnetic anisotropy changes of the system induced by the MNP assembly can be measured by ferromagnetic resonance spectroscopy as shifts in the resonance field. With a total assay time of ca. 120 min, the proposed biosensor offers a limit of detection of 6 fM with a dynamic detection range spanning 5 orders of magnitude. The specificity of the system is validated by testing different microRNAs and salmon sperm DNA. Endogenous microRNAs extracted from Oryza sativa leaves are tested with both quantitative reverse transcription-PCR and our approach, showing comparable performances with a Pearson correlation coefficient >0.9 (n = 20).

Multienzymatic disintegration of DNA-scaffolded magnetic nanoparticle assembly for malarial mitochondrial DNA detection

Early diagnosis of malaria can prevent the spread of disease and save lives, which, however, remains challenging in remote and less developed regions. Here we report a portable and low-cost optomagnetic biosensor for rapid amplification and detection of malarial mitochondrial DNA. Bioresponsive magnetic nanoparticle assemblies are constructed by using nucleic acid scaffolds containing endonucleolytic DNAzymes and their substrates, which can be activated by the presence of target DNA and self-disintegrated to release magnetic nanoparticles for optomagnetic quantification. Specifically, target molecules can induce padlock probe ligation and subsequent one-pot homogeneous cascade reactions consisting of nicking-enhanced rolling circle amplification, DNAzyme-assisted nucleic acid recycling, and strand-displacement-driven disintegration of the magnetic assembly. With an optimized magnetic actuation process for reaction acceleration, a detection limit of 1 fM can be achieved by the proposed biosensor with a total assay time of ca. 90 min and a dynamic detection range spanning 3 orders of magnitude. The robustness of the system was validated by testing target molecules spiked in 5% serum samples. Clinical sample validation was conducted by testing malaria-positive clinical blood specimens, obtaining quantitative results concordant with qPCR measurements.

A simulation study of magnetic nanoparticle clustering in a fluid flow

The assembly of magnetic nanoparticles has been promisingly used in biomedical applications. Several computational studies have addressed the study of cluster formation in the colloidal regime. However, these studies did not mention the formation of clusters in nonequilibrium conditions, such as fluid flow. To fill this gap, we develop computational models of magnetohydrodynamic systems to study their behavior within a flow in terms of cluster shape formation. All simulations were performed by Verlet integration through LAMMPS, a molecular dynamics framework. Through simulations, we discover that the fluid flow promotes formation of non-linear clusters, and linear clusters tend to orient toward the direction of the flow. These phenomena are investigated by using the equilibrium of magnetic torque and fluid torque. The analysis shows that the formation of non-linear clusters are mainly assisted by a bias-orientation of the unstable linear clusters, while the bias-orientation is originated from the torque cancellation in the direction of the flow.

Dynamically Tunable Assemblies of Superparamagnetic Nanoparticles Stabilized with Liquid Crystal-like Ligands in Organic Thin Films.

The process of arranging magnetic nanoparticles (MNPs) into long-range structures that can be dynamically and reversibly controlled is challenging, although interesting for emerging spintronic applications. Here, we report composites of MNPs in excess of LC-like ligands as promising materials for MNP-based technologies. The organic part ensures the assembly of MNP into long-range ordered phases as well as precise and temperature-reversible control over the arrangement. The dynamic changes are fully reversible, which we confirm using X-ray diffraction (XRD). This methodology allows for the precise control of the nanomaterial's structure in a thin film at different temperatures, translating to variable unit cell parameters. The composition of the materials (XPS, TGA), their structure (XRD), and magnetic properties (SQUID) were performed. Overall, this study confirms that LC-like materials provide the ability to dynamically control the magnetic nanoparticles in thin films, particularly the reversible control of their self-organization.

A Simple and Versatile Strategy for Oriented Immobilization of His-Tagged Proteins on Magnetic Nanoparticles.

Oriented and covalent immobilization of proteins on magnetic nanoparticles (MNPs) is particularly challenging as it requires both the functionality of the protein and the colloidal stability of the MNPs to be preserved. Here, we describe a simple, straightforward, and efficient strategy for MNP functionalization with proteins using metal affinity binding. Our method involves a single-step process where MNPs are functionalized using a preformed, ready-to-use nitrilotriacetic acid-divalent metal cation (NTA-M2+) complex and polyethylene glycol (PEG) molecules. As a proof-of-concept, we demonstrate the oriented immobilization of a recombinant cadherin fragment engineered with a hexahistidine tag (6His-tag) onto the MNPs. Our developed methodology is simple and direct, enabling the oriented bioconjugation of His-tagged cadherins to MNPs while preserving protein functionality and the colloidal stability of the MNPs, and could be extended to other proteins expressing a polyhistidine tag. When compared to the traditional method where NTA is first conjugated to the MNPs and afterward free metal ions are added to form the complex, this novel strategy results in a higher functionalization efficiency while avoiding MNP aggregation. Additionally, our method allows for covalent bonding of the cadherin fragments to the MNP surface while preserving functionality, making it highly versatile. Finally, our strategy not only ensures the correct orientation of the protein fragments on the MNPs but also allows for the precise control of their density. This feature enables the selective targeting of E-cadherin-expressing cells only when MNPs are decorated with a high density of cadherin fragments.

Realizing optimized interfacial polarization and impedance matching with CNT-confined Co nanoparticles in hollow carbon microspheres for enhanced microwave absorption

The hollow porous structure with exceptional interfacial effect and customizable internal environment shows significant potential for application as electromagnetic shielding and absorption materials. However, designing hollow porous electromagnetic absorbers with both desirable impedance matching and high loss capability remains a challenge. Herein, 3D hollow porous electromagnetic microspheres were constructed by assembling 0D Co magnetic nanoparticles, 1D carbon nanotubes, and 2D carbon nanosheets. Due to the sufficient sites for Co2+ riveting, the high loading of magnetic carbon nanotubes (CoNC) and porous carbon spheres formed high-density interfaces, enhancing the interfacial polarization. Furthermore, high-density CoNC were grown in situ on the hollow porous carbon (HPC) microsphere, forming a highly dispersed 3D magnetic network that inhibited the aggregation of magnetic nanoparticles and enhanced magnetic coupling. Therefore, the as-prepared CoNC/HPC microspheres exhibited excellent microwave absorption (MA) performance, with a minimum reflection loss of -33.2 dB and an effective bandwidth of 5.5 GHz at a thickness of only 1.8 mm. The interfacial polarization mechanism for enhanced MA performance was demonstrated by electron holography and density functional theory calculations. Magnetic holography and micromagnetic simulations also revealed magnetic confinement and coupling mechanism. This work provides a new approach for designing electromagnetic absorbers with optimized impedance matching and loss capability.

Effect of dipolar interaction on magnetic properties of magnetite nanoparticles system: a simulation study

Superparamagnetic iron oxide nanoparticles are a potential candidate for novel research. The inter-particle interactions play a significant role in determining the overall magnetic behavior of a magnetic nanoparticle assembly, especially in dipolar interaction. In this paper, we have synthesized a practical sample and then applied an atomistic spin model simulation study with input parameters obtained from experimental measurements to investigate the influence of the dipolar interaction on the magnetic properties of Fe3O4 magnetite nanoparticles.

Probing magnetization dynamics of iron oxide nanoparticles using a point-probe magneto-optical method

Magnetic nanoparticles (MNPs) are promising as local heat generators for magnetic hyperthermia under AC magnetic fields. The heating efficacy of MNPs is determined by the AC hysteresis loop area, which in turn is affected by the dynamic magnetic properties of the nanoparticles. Whilst inductive-based AC magnetometers can measure the average magnetic behavior of samples, the use of the magneto-optical Faraday effect with a focused laser spot allows point-probe measurements to be made, and without some of the magnetic field limitations imposed by inductive methods. In this work, the AC magnetic properties of different sized iron oxide MNPs in suspension were measured by AC magnetometry and AC susceptibility techniques. AC hysteresis loops measured by magneto-optical magnetometry were validated using a commercial inductive AC magnetometer, and compared to the magnetization relaxation behavior revealed by fitting the AC susceptibility data. The spatial sensitivity of the point-probe magneto-optical method is also demonstrated by measuring the AC hysteresis loop from large (>1 μm) MNP aggregates dried onto glass slides. These aggregated particles are found to be magnetically softer than in their suspension form, suggesting interparticle coupling mechanisms could occur when the nanoparticles form dense aggregates.