Magnetic Nanoparticle Clusters Research Articles

Abstract B026: Rotational magnetic drug targeting for leptomeningeal metastases

Abstract Background: Magnetic nanoparticles (MNPs) have potential for enhancing the delivery of therapeutic molecules to cancer cells and micronodules, including non-obstructing metastases within cerebrospinal fluid (CSF) pathways. Rotational magnetic drug targeting (rMDT) takes advantage of the surface-walking capability of clusters of MNPs, which can be activated remotely. Here, we present data related to 1) the creation, characterization, and in vitro testing of a variety of MNPs utilized with bound or unbound chemotherapeutic agents, and 2) the design and construction of four different magnetomotive systems used to propel MNPs at clinically-relevant distances. The goal was to create an in vitro model mimicking conditions found in patients with leptomeningeal metastases. Methods: Gold-iron alloy nanoparticles were combined with biotinylated etoposide via the streptavidin-biotin interaction. Unbound MNPs were tested with etoposide and doxorubicin. MNPs were characterized by techniques including electron microscopy, Zeta potential analysis, and dynamic light scattering. 3D-printed and acrylic trays were used as conduits for measuring translational motion over distances up to 30 cm through saline, culture media, and artifical CSF. MNP velocities were determined by videography. For propelling the MNPs, one electromagnetic system used a Helmholtz pair of coils on each side of an underlying perpendicular coil. The second electromagnetic system utilized 2 angled coils. Two rotating permanent magnet systems used neodymium-boron-iron magnets of different sizes and rotational speeds. Cultured cells included fibroblasts, lung cancer, glioblastoma, and medulloblastoma cell lines. Light microscopy and cytotoxicty assays (by MTT and trypan blue exclusion) were used to assess preservation of tumoricidal activity. Results: In unbound MNP studies, both etoposide and doxorubin could be dispersed over physiologic distances through saline and artificial CSF at velocities exceeding 1 cm/sec - much faster than by diffusion alone. Drugs conveyed in this manner could be transported at 37°C across cell surfaces and retain tumoricidal effect on cultured cells. With rotating magnets, MNPs could be moved against a saline flow rate of 1 cm/sec. In bound MNP studies, true rMDT was possible - all four magnetomotive systems could be shut off, depositing the MNP-drug conjugate at the desired location. Rotating permanent magnets were found to be advantageous for unilateral device design; electromagnetic devices, however, are more likely to be compatible with concurrent magnetic particle imaging (currently under development). Conclusions: These in vitro findings indicate that rMDT within CSF pathways is feasible and should advance to animal studies. Bound MNPs may prove to be more useful for intrathecal use (administered via lumbar puncture or Ommaya reservoir), considering dilutional effects and CSF flow. An improved ability to direct therapeutic agents within CSF would represent a major step forward in the treatment of patients with leptomeningeal metastases. Citation Format: Herbert Engelhard, Alexander Willis, Tolou Shokuhfar, Lamar Mair. Rotational magnetic drug targeting for leptomeningeal metastases [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr B026.

Resonance-Based Sensing of Magnetic Nanoparticles Using Microfluidic Devices with Ferromagnetic Antidot Nanostructures.

We demonstrated resonance-based detection of magnetic nanoparticles employing novel designs based upon planar (on-chip) microresonators that may serve as alternatives to conventional magnetoresistive magnetic nanoparticle detectors. We detected 130 nm sized magnetic nanoparticle clusters immobilized on sensor surfaces after flowing through PDMS microfluidic channels molded using a 3D printed mold. Two detection schemes were investigated: (i) indirect detection incorporating ferromagnetic antidot nanostructures within microresonators, and (ii) direct detection of nanoparticles without an antidot lattice. Using scheme (i), magnetic nanoparticles noticeably downshifted the resonance fields of an antidot nanostructure by up to 207 G. In a similar antidot device in which nanoparticles were introduced via droplets rather than a microfluidic channel, the largest shift was only 44 G with a sensitivity of 7.57 G/ng. This indicated that introduction of the nanoparticles via microfluidics results in stronger responses from the ferromagnetic resonances. The results for both devices demonstrated that ferromagnetic antidot nanostructures incorporated within planar microresonators can detect nanoparticles captured from dispersions. Using detection scheme (ii), without the antidot array, we observed a strong resonance within the nanoparticles. The resonance's strength suggests that direct detection is more sensitive to magnetic nanoparticles than indirect detection using a nanostructure, in addition to being much simpler.

Estimation of biomolecule amount by analyzing magnetic nanoparticle cluster distributions from alternating current magnetization spectra for magnetic biosensing

The hydrodynamic size distribution of magnetic nanoparticle (MNP) clusters is crucial for determining the amounts of biomolecules by analyzing the distributions of the Brownian relaxation time in the corresponding alternating current (AC) magnetization spectra. This study proposes a method for estimating the distribution of MNP clusters from recorded AC magnetization spectra using an experimental-based model. The proposed model is used to form a matrix equation that comprises the distribution and AC magnetization spectra of MNP clusters, and the MNP–biomolecule cluster distribution is obtained by solving an inverse problem. The results show that the variations in the MNP clusters distribution estimated from the model correspond to those measured by dynamic light scattering. The MNP cluster distributions estimated using the experimental model were used to estimate streptavidin concentrations in the range of 0.19–3.38 μM. The estimated values agree accurately with the true values, demonstrating the feasibility of the proposed method for biosensing.

Synthesis of a magneto-chromatic tunable Fe3O4-HPAM colloid

Colloids of soft magnetic (Fe3O4) submicrometer particles, formed by magnetic nanoparticle clusters, coated with a polyelectrolyte (hydrolyzed polyacrylamide; HPAM) were fabricated successfully in situ with a highly controllable chemical approach. The formation mechanism of submicron particles was analyzed under the amounts of HPAM, urea, citrate, and metallic precursors. This mechanism was followed by SEM. The results showed that the physicochemical properties of the HPAM favored physical interactions with the reactants, promoting the formation of dense-packed magnetic micrometer clusters in one-step synthesis. The results showed that the physicochemical properties of the HPAM favored physical interactions with the reactants, promoting the formation of dense-packed magnetic micrometer clusters in one-step synthesis. The different estimated radii of these particles in solution (hydrodynamic and gyration) and dried (internal radius) decrease when the HPAM amount increases. Moreover, the particles exhibited a superparamagnetic behavior with a magnetization of 48.2 emu/g, 50.3 emu/g, and 54.3 emu/g when the amounts were 0.5 g, 1 g, and 2g of HPAM, respectively. Consequently, the optical response of the colloids to the application of a rotating magnetic field (RMF) parallel to the horizontal plane where they were located exhibited a behavior similar to photonic structures since their reflection spectrum showed a periodic diffraction color that closely matches the frequency of the RMF.

Focusing and rotating magnetic nanoparticle clusters for fast ablation of thrombus

Focusing and rotating magnetic nanoparticle clusters for fast ablation of thrombus

Analyte‐Driven Clustering of Bio‐Conjugated Magnetic Nanoparticles

AbstractThe dynamics of bio‐conjugated magnetic nanoparticles suspended in buffer‐saline solutions containing target proteins (i.e., analytes) is investigated numerically on a mesoscopic level. To simulate the dispersion of magnetic nanoparticles the dissipative particle dynamics is employed, which allows to study rather large systems, while still retaining important microscopic nanoparticle properties. In addition, the method is coupled to the Landau–Lifshitz–Gilbert equation, describing the dynamics of the magnetic nanocrystals within the macrospin approximation. The binding of multivalent analytes to the recognition ligands of the nanoparticles leads to the formation of clusters of magnetic nanoparticles, which in turn drastically changes the macroscopic magnetic response of the solution. Such colloidal changes are experimentally observable, allowing to explore new approaches to quantify the analyte amount. The ratio of the concentrations between the analytes (biomarkers) and the recognition ligands on the nanoparticles is found to play an important role in the formation and hydrodynamic size of the clusters. The proposed computational framework has great potential to be integrated with experimental efforts to advance the development of nanoparticle‐based biosensors for disease diagnostics and other biomedical applications.

Specific absorption rate in quasispherical and elongated aggregates of magnetite nanoparticles: Experimental characterization and numerical simulation

Assemblies of magnetite nanoparticles created by the ultrasonic mechanocavitation in a viscous liquid have been obtained for use in magnetic hyperthermia. The magnetite nanoparticles inherit the perfect crystal structure of the original coarse-grained magnetite powder, with characteristic sizes of 0.2–8 μm, and have a high saturation magnetization, Ms = 92 emu/g, close to the value of pure magnetite. Measurements of the specific absorption rate (SAR) of assemblies in an alternating (ac) magnetic field showed a significant dependence of SAR on the nanoparticle concentration, as well as on the shape of particle macroaggregates. A 4-fold increase in the SAR of elongated clusters of particles oriented parallel to the action of ac magnetic field was found in comparison with an assembly of quasi-spherical clusters. In addition a sharp dependence of the SAR of an assembly of elongated clusters on the ac magnetic field direction with respect to the cluster orientation axis was revealed. The results obtained are in qualitative agreement with the results of numerical simulation of dense clusters of magnetic nanoparticles based on the solution of the stochastic Landau-Lifshitz equation.

Tubulins show susceptibility to magnetic nanoparticle interaction.

Low piconewton forces can induce axonal specification and outgrowth in neurons. However, the secondary mechanism underlying force-mediated axon specification is poorly understood. Within the axon shaft, microtubules, composed of α and β tubulin dimers, are stabilized by the protein Tau. These microtubules polymerize toward the axonal tip, where actin provides a tensile force against the membrane to maintain or extend the structure of the tip. We hypothesize that exogenous forces manipulate one or more of these structural proteins, which could induce axonal lineage. Our previous work has shown that hTau40, the brain's most ubiquitous isoform of Tau, can be directly dragged by internalized magnetic nanoparticles (MNPs) within primary neurons. Here, we sought to establish whether this direct relationship between the nanoparticles and Tau applied to other axonal structural proteins. We transduced (BacMam) dissociated primary cortical neurons (rat, E18) at the day in vitro two (DIV 2) with one of three vectors containing a gene for a fluorescently labeled structural protein: α-tubulin-mCherry, β-tubulin-GFP, or β-actin-GFP. At DIV 4, the neurons were incubated for 24 h with starch-NH2-coated, far-red fluorescent magnetic nanoparticles (d: 100 nm) at 10 µg/mL. Cells were then washed and imaged using a Leica DMi8 inverted fluorescent microscope to determine whether there was high colocalization, indicating direct interaction, between the MNPs and the fluorescent proteins. Compared to the high-intensity protein spots, α-tubulin-mCherry showed the greatest percentage of correlated MNP clusters (45.7 ± 6.8 %, n = 11 cells), followed by β-tubulin-GFP, with 36.9 ± 11.7 % (n = 6) of high protein spots correlated to MNP clusters. Only 8.27 ± 5.32% (n = 7) of β-actin-GFP spots correlating to MNP clusters. These preliminary data suggest tubulins may be more susceptible to direct nanomagnetic force manipulation (mean ± SEM).

Poly(vinyl alcohol)/sodium alginate/magnetite composites: magnetic force microscopy for tracking magnetic domains.

Hydrogels of poly(vinyl alcohol) (PVA)/sodium alginate (SA), and magnetic nanoparticles (MNPs) were prepared by solvent casting in the absence and in the presence of magnets, in order to obtain MNPs distributed randomly (PVA/SA-rMNP) and magnetically oriented MNPs (PVA/SA-gMNP) in the polymer matrix. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques were used to evaluate the topography and to map the distribution of magnetic domains in the polymer matrix, respectively. The tip-surface distance (lift distance) of 50 nm during the MFM analyses facilitated the mapping of magnetic domains because the van der Waals forces were minimized. The magnetic signal stemming from clusters of MNPs were more easily identified than that from isolated MNPs. PVA and SA, PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings with surface roughness (Ra) values of 3.8 nm, 28.7 nm, and 49.8 nm, respectively, were tested for the proliferation of mouse hippocampal HT-22 cells. While PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings preserved cell viability >70% in comparison to the control (plastic plate) over 48 h, cell proliferation tended to decrease on surfaces with higher Ra values (PVA/SA-gMNP). These findings showed that the orientation of magnetic domains led to an increase of surface roughness, which decreased the viability of HT-22 cells. Thus, these results might be interesting for situations, where the control of cell proliferation is necessary.

Monitoring magnetic nanoparticle clustering and immobilization with thermal noise magnetometry using optically pumped magnetometers.

Thermal noise magnetometry (TNM) is a recently developed magnetic characterization technique where thermally induced fluctuations in magnetization are measured to gain insight into nanomagnetic structures like magnetic nanoparticles (MNPs). Due to the stochastic nature of the method, its signal amplitude scales with the square of the volume of the individual fluctuators, which makes the method therefore extra attractive to study MNP clustering and aggregation processes. Until now, TNM signals have exclusively been detected by using a superconducting quantum interference device (SQUID) sensor. In contrast, we present here a tabletop setup using optically pumped magnetometers (OPMs) in a compact magnetic shield, as a flexible alternative. The agreement between results obtained with both measurement systems is shown for different commercially available MNP samples. We argue that the OPM setup with low complexity complements the SQUID setup with high sensitivity and bandwidth. Furthermore, the OPM tabletop setup is well suited to monitor aggregation processes because of its excellent sensitivity in lower frequencies. As a proof of concept, we show the changes in the noise spectrum for three different MNP immobilization and clustering processes. From our results, we conclude that the tabletop setup offers a flexible and widely adoptable measurement unit to monitor the immobilization, aggregation, and clustering of MNPs for different applications, including interactions of the particles with biological systems and the long-term stability of magnetic samples.

A novel magnetic cluster modified palladium-cellulose nanocrystal hybrids as recyclable catalyst for 4-nitrophenol reduction

The development of noble metal catalysts with high catalytic performance and low metal loading has attracted a lot of interest. However, the separation of the used nanoscale catalyst from the process is challenging. Most of the separation system, such as resin or membrane leads to a sacrifice of high surface area as well as catalytic efficiency. Herein, two series of recyclable catalysts were synthesized by loading palladium (Pd) particles onto melamine formaldehyde (MF) modified cellulose nanocrystals (CNC) and dopamine (DA) coated CNC. In situ co-precipitation of magnetic nanoparticle (MNP) clusters were used to impart magnetic characteristic to the catalysts. This magnetic cluster successfully achieved high magnetization without aggregation. The amount of palladium precursor added to the catalytic systems was optimized, where 10-Pd-PDC yielded 10.83 ± 2.43 nm discrete Pd loaded hybrids. The catalytic performance was assessed by the reduction of 4-nitrophenol (4-NP) in the presence of sodium borohydrides (NaBH 4 ). The 4-NP reduction mechanisms were analyzed using the Langmuir-Hinshelwood model and the apparent rate constant k (s -1 ), turnover frequency (TOF, h -1 ) and activity factors (s -1 g -1 ) were determined to be 2.142 × 10 -3 , 305.82 and 535.5 using MNP2-Pd-MC respectively. An induction time was observed for MNP4 or 5-Pd-PDC, where was attributed to the unignitable diffusion time for reagents to cross the thick PDA and MNP layer. The separation efficiency of the magnetic catalysts was evaluated by monitoring the absorbance at 400 nm as a function of separation time, and the MNP2-Pd-MC could be recycled 7 times without severe loss. Pd-MF-CNC displayed excellent catalytic performance for the reduction of 4-NP, while Pd-PDA-CNC possessed an inferior catalytic reactivity due to the reduced catalytic surface area. The developed templated MNP could be extended to other systems allowing for the recycling and reuse of the catalysts.

Multifunctional Core@Satellite Magnetic Particles for Magnetoresistive Biosensors.

Magnetoresistive (MR) biosensors combine distinctive features such as small size, low cost, good sensitivity, and propensity to be arrayed to perform multiplexed analysis. Magnetic nanoparticles (MNPs) are the ideal target for this platform, especially if modified not only to overcome their intrinsic tendency to aggregate and lack of stability but also to realize an interacting surface suitable for biofunctionalization without strongly losing their magnetic response. Here, we describe an MR biosensor in which commercial MNP clusters were coated with gold nanoparticles (AuNPs) and used to detect human IgG in water using an MR biochip that comprises six sensing regions, each one containing five U-shaped spin valve sensors. The isolated AuNPs (satellites) were stuck onto an aggregate of individual iron oxide crystals (core) so that the resulting core@satellite magnetic particles (CSMPs) could be functionalized by the photochemical immobilization technique—an easy procedure that leads to oriented antibodies immobilized upright onto gold. The morphological, optical, hydrodynamic, magnetic, and surface charge properties of CSMPs were compared with those exhibited by the commercial MNP clusters showing that the proposed coating procedure endows the MNP clusters with stability and ductility without being detrimental to magnetic properties. Eventually, the high-performance MR biosensor allowed us to detect human IgG in water with a detection limit of 13 pM (2 ng mL–1). Given its portability, the biosensor described in this paper lends itself to a point-of-care device; moreover, the features of the MR biochip also make it suitable for multiplexed analysis.

Parallel Multichannel Assessment of Rotationally Manipulated Magnetic Nanoparticles.

BackgroundRotational manipulation of chains or clusters of magnetic nanoparticles (MNPs) offers a means for directed translation and payload delivery that should be explored for clinical use. Multiple MNP types are available, yet few studies have performed side-by-side comparisons to evaluate characteristics such as velocity, movement at a distance, and capacity for drug conveyance or dispersion.PurposeOur goal was to design, build, and study an electric device allowing simultaneous, multichannel testing (e.g., racing) of MNPs in response to a rotating magnetic field. We would then select the “best” MNP and use it with optimized device settings, to transport an unbound therapeutic agent.MethodsA magnetomotive system was constructed, with a Helmholtz pair of coils on either side of a single perpendicular coil, on top of which was placed an acrylic tray having multiple parallel lanes. Five different MNPs were tested: graphene-coated cobalt MNPs (TurboBeads™), nickel nanorods, gold-iron alloy MNPs, gold-coated Fe3O4 MNPs, and uncoated Fe3O4 MNPs. Velocities were determined in response to varying magnetic field frequencies (5–200 Hz) and heights (0–18 cm). Velocities were normalized to account for minor lane differences. Doxorubicin was chosen as the therapeutic agent, assayed using a CLARIOstar Plus microplate reader.ResultsThe MMS generated a maximal MNP velocity of 0.9 cm/s. All MNPs encountered a “critical” frequency at 20–30 Hz. Nickel nanorods had the optimal response based on tray height and were then shown to enable unbound doxorubicin dispersion along 10.5 cm in <30 sec.ConclusionA rotating magnetic field can be conveniently generated using a three-coil electromagnetic device, and used to induce rotational and translational movement of MNP aggregates over mesoscale distances. The responses of various MNPs can be compared side-by-side using multichannel acrylic trays to assess suitability for drug delivery, highlighting their potential for further in vivo applications.

Hierarchical iron oxide nanocomposite: Bundle-like morphology, magnetic properties and potential biomedical application

Controlled spatial arrangements of superparamagnetic iron oxide nanoparticles (SPIONs) in complex nanostructures determine fine tuning of physico-chemical properties which, in turn, may lead to new practical applications. We report here on newly observed properties of hierarchical SPIONs nanostructure with bundle-like morphology, also known as nanobundles. Colloidal chemical processes and sol-gel synthesis were used for the synthesis of nanobundles, i.e. i) self-assembly of SPIONs into magnetic nanoparticle clusters, ii) their magnetic assembly to the nanochains, and finally iii) formation of bundle-like hierarchical nanostructure. An XRPD measurements show spinel crystal structure of maghemite/magnetite nanoparticles, EDS analysis reveals Fe, Si and O as main elements whereas SEM/TEM analysis show silica-coated magnetic nanoclusters (∼100 nm) and their hierarchical assemblies with bundle-like morphology of ∼8 μm length and ∼1 μm width. TEM analysis revealed core-shell nature of iron oxide nanoparticle clusters with their size of around 80 nm that were coated by an amorphous silica shell with thickness of ∼15 nm. The nanoclusters in the core are constructed of maghemite/magnetite nanoparticle assembly with primary iron oxide nanoparticle size about 10 nm. The magnetization M data as a function of an applied external magnetic field H were successfully fitted by the Langevin function, whence the magnetic moment μp = 19256 μB, and the diameter d = 9.6 nm of nanoparticles were determined. Microsized bundle-like particles are superparamagnetic, magnetically guidable and possess high transverse relaxivity of r2 = 397.8 mM−1s−1. Magnetic properties and such high value of transverse relaxivity holds promise for nanobundles application in MRI imaging (MRI contrast agent), as nanobundles may enhance the magnetic field in their surroundings and enhance proton relaxation processes. Our nanobundles can open new opportunities in the biomedical applications, magnetic separation, photonic crystals and magnetic liquid manipulation and can be inspiration for synthesizing novel self-assembled nanoparticle structures.

The construct of triple responsive nanocomposite and its antibacterial effect

The current serious mismatch between the increasing severity of bacterial infections and antibiotic production capacity urgently requires the emergence of novel antimicrobial materials. In this paper, dopamine methacrylamide (DMA) and N-isopropylacrylamide (NIPAM) were polymerized as the monomers into a block copolymer poly(dopamine methacrylamide-block-N-isopropylacrylamide) (P(DA-NIP)) and then encapsulated with polydopamine-coated magnetic nanoparticle clusters (MNC) to produce an antibacterial nanocomposite (MNC@P(DA-NIP)). This nanocomposite has triple responses respectively to light, heat and magnetism, which endow MNC@P(DA-NIP) with the abilities to kill bacteria effectively and capture/release bacteria conveniently. Under near-infrared (NIR) light irradiation, MNC@P(DA-NIP) could significantly elevate the temperature through photothermal conversion. The increased temperature favored both the capture of bacteria on MNC@P(DA-NIP), and the damage of bacterial cells, causing bacterial death almost completely. While low temperatures could promote the release of dead bacteria from the nanocomposites, might through the recovery of the hydrophilic state of the outlayer PNIPAM. Moreover, thanks to the magnetic responsibility, MNC@P(DA-NIP) could be easily separated from the bacterial cells and perform better biofilm penetration. The results showed that the antibacterial effect of MNC@P(DA-NIP) was 3.5 times higher than that of MNC, and the recycling capacity of MNC@P(DA-NIP) was better than MNC@PDA. What’s more, MNC@P(DA-NIP) possessed the excellent anti-biofilm properties under magnetic field (MF) and NIR. The most important features of the triple-responsive nanocomposites are excellent antibacterial effect, good recyclability and easy preparation, which provide the nanocomposites with great potential in eliminating harmful bacterial cells.

Controlling local relaxation in small clusters of magnetic nanoparticles

We investigate the local (particle level) and averaged magnetic relaxation characteristics in linear chain-like agglomerates of k magnetic nanoparticles (MNPs) or k-mers using computer simulations. The local relaxation behaviour is dictated by the corresponding dipolar field acting on the nanoparticle, irrespective of k-mer size. There is a wide variation in local relaxation characteristics as a function of nanoparticle position in a small nanocluster. On the other hand, there is more uniformity in the local relaxation response with a larger k-mer, except for MNPs at the boundary. Interestingly, there is a smooth decay of magnetization with small hd, independent of cluster size. In contrast, the magnetization ceases to relax in the presence of substantial dipolar interaction strength. Remarkably, the local Néel relaxation time τNi is directly proportional to the corresponding dipolar field. Likewise, the averaged Néel relaxation time τN also depends strongly on the k-mer size and hd.

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stiffness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiments and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.

Tailoring Local Hysteresis in Small Clusters of Dipolar Interacting Magnetic Nanoparticles

Using first-principle calculations and kinetic Monte Carlo simulation, we study the local and averaged hysteresis in tiny clusters of [Formula: see text] magnetic nanoparticles (MNPs) or [Formula: see text]-mers. We also analyze the variation of local dipolar field acting on the constituent nanoparticles as a function of the external magnetic field. The dipolar interaction is found to promote chain-like arrangement in such a cluster. Irrespective of cluster size, the local hysteresis response depends strongly on the corresponding dipolar field acting on a nanoparticle. In a small [Formula: see text]-mer, there is a wide variation in local hysteresis as a function of nanoparticle position. On the other hand, the local hysteresis is more uniform for larger [Formula: see text]-mer, except for MNPs at the boundary. In the case of superparamagnetic nanoparticle and weak dipolar interaction, the local hysteresis loop area [Formula: see text] is minimal and depends weakly on the [Formula: see text]-mer size. While for ferromagnetic counterpart, [Formula: see text] is considerably large even for weakly interacting MNPs. The value of [Formula: see text] is found to be directly proportional to the dipolar field acting on the nanoparticle. The dipolar interaction and [Formula: see text]-mer size also enhance the coercivity and remanence. There is always an increase in [Formula: see text] with cluster size and dipolar interaction strength. Similarly, the averaged hysteresis loop area [Formula: see text] also depends strongly on the [Formula: see text]-mer size, particle size and dipolar interaction strength. [Formula: see text] and [Formula: see text] always increase with [Formula: see text]-mer size and dipolar interaction strength. Interestingly, the value of [Formula: see text] saturates for [Formula: see text] and considerable dipolar interaction irrespective of particle size. We believe that this work would help understand the intricate role of dipolar interaction on hysteresis and the organizational structure of MNPs and their usage in drug delivery and hyperthermia applications.

Biocompatible Superparamagnetic Europium-Doped Iron Oxide Nanoparticle Clusters as Multifunctional Nanoprobes for Multimodal In Vivo Imaging.

Magnetic nanoparticle clusters composed of primary magnetic nanoparticles can not only significantly enhance the magnetic properties of the assembly but also retain the superparamagnetic properties of the individual primary nanoparticle, which is of great significance for promoting the development of multifunctional advanced materials. Herein, water-soluble biocompatible and superparamagnetic europium-doped iron oxide nanoparticle clusters (EuIO NCs) were directly synthesized by a simple one-pot method. The obtained EuIO NCs have excellent water solubility, colloidal stability, and biocompatibility. Europium doping significantly improved the contrast enhancement effect of EuIO NCs in T1-weighted MR imaging. In addition, EuIO NCs can be functionalized by active molecules, and the rhodamine123-functionalized EuIO NCs have long circulation time and excellent fluorescence imaging performance in vivo. This study provides a simple strategy for the design and construction of a novel multifunctional magnetic nanoplatform and provides solutions for the development of multimodal imaging probes and the diagnosis of disease.

Zwitterion-Coated Colloidal Magnetic Nanoparticle Clusters for Reduced Nonspecific Adsorption of Biomolecules.

This paper demonstrates fabrication of silica-shell-coated magnetic nanoparticle clusters (SMNCs) and subsequent surface engineering of SMNCs to produce surface-modified SMNCs that have zwitterionic and primary amine ligands (SMNC-ZW/Am). SMNC-ZW/Am was passivated by zwitterionic ligands for improved colloidal stability and reduced nonspecific adsorption and by primary amine ligands for facilitated conjugation with biomolecules. Hydrodynamic (HD) size and zeta potential of SMNC-ZW/Am could be flexibly tuned by controlling the relative amounts of zwitterionic and primary amine ligands. SMNC-ZW/Am had higher colloidal stability in high salt concentration and broad pH range than did bare SMNC. Nonspecific adsorption with biomolecules onto SMNC-ZW/Am surface was significantly suppressed by the zwitterionic ligands. The facile bioconjugation capability of SWNC-ZW/Am enabled conjugation of biotin and antibody to the SWNC-ZW/Am surface. Biomolecule-conjugated SMNC-ZW/Am showed specific binding affinity to streptavidin and Salmonella bacteria, with reduced nonspecific adsorption; therefore, SWMC-ZW/Am has potential use as an antifouling nanosubstrate for separation and bioanalysis.