Nanomaterials

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3 pages, 173 KiB

Open AccessEditorial

Applications and Properties of Magnetic Nanoparticles

by Paolo Arosio

Nanomaterials 2021, 11(5), 1297; https://doi.org/10.3390/nano11051297 - 14 May 2021

Cited by 6 | Viewed by 2707

Abstract

In the last few decades, magnetic nanoconstructs have attracted increasing attention due to, among others, their specific magnetic properties and huge number of applications in completely different fields [...] Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

Research

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16 pages, 2230 KiB

Open AccessArticle

Comparative Modeling of Frequency Mixing Measurements of Magnetic Nanoparticles Using Micromagnetic Simulations and Langevin Theory

by Ulrich M. Engelmann, Ahmed Shalaby, Carolyn Shasha, Kannan M. Krishnan and Hans-Joachim Krause

Nanomaterials 2021, 11(5), 1257; https://doi.org/10.3390/nano11051257 - 11 May 2021

Cited by 10 | Viewed by 3432

Abstract

Dual frequency magnetic excitation of magnetic nanoparticles (MNP) enables enhanced biosensing applications. This was studied from an experimental and theoretical perspective: nonlinear sum-frequency components of MNP exposed to dual-frequency magnetic excitation were measured as a function of static magnetic offset field. The Langevin [...] Read more.

Dual frequency magnetic excitation of magnetic nanoparticles (MNP) enables enhanced biosensing applications. This was studied from an experimental and theoretical perspective: nonlinear sum-frequency components of MNP exposed to dual-frequency magnetic excitation were measured as a function of static magnetic offset field. The Langevin model in thermodynamic equilibrium was fitted to the experimental data to derive parameters of the lognormal core size distribution. These parameters were subsequently used as inputs for micromagnetic Monte-Carlo (MC)-simulations. From the hysteresis loops obtained from MC-simulations, sum-frequency components were numerically demodulated and compared with both experiment and Langevin model predictions. From the latter, we derived that approximately 90% of the frequency mixing magnetic response signal is generated by the largest 10% of MNP. We therefore suggest that small particles do not contribute to the frequency mixing signal, which is supported by MC-simulation results. Both theoretical approaches describe the experimental signal shapes well, but with notable differences between experiment and micromagnetic simulations. These deviations could result from Brownian relaxations which are, albeit experimentally inhibited, included in MC-simulation, or (yet unconsidered) cluster-effects of MNP, or inaccurately derived input for MC-simulations, because the largest particles dominate the experimental signal but concurrently do not fulfill the precondition of thermodynamic equilibrium required by Langevin theory. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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12 pages, 3000 KiB

Open AccessArticle

Highly Sensitive Fluorescent Detection of Acetylcholine Based on the Enhanced Peroxidase-Like Activity of Histidine Coated Magnetic Nanoparticles

by Hong Jae Cheon, Quynh Huong Nguyen and Moon Il Kim

Nanomaterials 2021, 11(5), 1207; https://doi.org/10.3390/nano11051207 - 1 May 2021

Cited by 9 | Viewed by 3490

Abstract

Inspired by the active site structure of natural horseradish peroxidase having iron as a pivotal element with coordinated histidine residues, we have developed histidine coated magnetic nanoparticles (His@MNPs) with relatively uniform and small sizes (less than 10 nm) through one-pot heat treatment. In [...] Read more.

Inspired by the active site structure of natural horseradish peroxidase having iron as a pivotal element with coordinated histidine residues, we have developed histidine coated magnetic nanoparticles (His@MNPs) with relatively uniform and small sizes (less than 10 nm) through one-pot heat treatment. In comparison to pristine MNPs and other amino acid coated MNPs, His@MNPs exhibited a considerably enhanced peroxidase-imitating activity, approaching 10-fold higher in catalytic reactions. With the high activity, His@MNPs then were exploited to detect the important neurotransmitter acetylcholine. By coupling choline oxidase and acetylcholine esterase with His@MNPs as peroxidase mimics, target choline and acetylcholine were successfully detected via fluorescent mode with high specificity and sensitivity with the limits of detection down to 200 and 100 nM, respectively. The diagnostic capability of the method is demonstrated by analyzing acetylcholine in human blood serum. This study thus demonstrates the potential of utilizing His@MNPs as peroxidase-mimicking nanozymes for detecting important biological and clinical targets with high sensitivity and reliability. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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22 pages, 4314 KiB

Open AccessArticle

Boosting Magnetoelectric Effect in Polymer-Based Nanocomposites

by Alexander Omelyanchik, Valentina Antipova, Christina Gritsenko, Valeria Kolesnikova, Dmitry Murzin, Yilin Han, Andrei V. Turutin, Ilya V. Kubasov, Alexander M. Kislyuk, Tatiana S. Ilina, Dmitry A. Kiselev, Marina I. Voronova, Mikhail D. Malinkovich, Yuriy N. Parkhomenko, Maxim Silibin, Elena N. Kozlova, Davide Peddis, Kateryna Levada, Liudmila Makarova, Abdulkarim Amirov and Valeria Rodionova Show full author list Hide full author list

Nanomaterials 2021, 11(5), 1154; https://doi.org/10.3390/nano11051154 - 28 Apr 2021

Cited by 37 | Viewed by 6143

Abstract

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In [...] Read more.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (α_ME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO₃ particles. Developed strategies allow us to increase the α_ME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe₂O₄ nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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13 pages, 2913 KiB

Open AccessArticle

The Heating Efficiency and Imaging Performance of Magnesium Iron Oxide@tetramethyl Ammonium Hydroxide Nanoparticles for Biomedical Applications

by Mohamed S. A. Darwish, Hohyeon Kim, Minh Phu Bui, Tuan-Anh Le, Hwangjae Lee, Chiseon Ryu, Jae Young Lee and Jungwon Yoon

Nanomaterials 2021, 11(5), 1096; https://doi.org/10.3390/nano11051096 - 23 Apr 2021

Cited by 13 | Viewed by 3119

Abstract

Multifunctional magnetic nanomaterials displaying high specific loss power (SLP) and high imaging sensitivity with good spatial resolution are highly desired in image-guided cancer therapy. Currently, commercial nanoparticles do not sufficiently provide such multifunctionality. For example, Resovist^® has good image resolution but with [...] Read more.

Multifunctional magnetic nanomaterials displaying high specific loss power (SLP) and high imaging sensitivity with good spatial resolution are highly desired in image-guided cancer therapy. Currently, commercial nanoparticles do not sufficiently provide such multifunctionality. For example, Resovist^® has good image resolution but with a low SLP, whereas BNF^® has a high SLP value with very low image resolution. In this study, hydrophilic magnesium iron oxide@tetramethyl ammonium hydroxide nanoparticles were prepared in two steps. First, hydrophobic magnesium iron oxide nanoparticles were fabricated using a thermal decomposition technique, followed by coating with tetramethyl ammonium hydroxide. The synthesized nanoparticles were characterized using XRD, DLS, TEM, zeta potential, UV-Vis spectroscopy, and VSM. The hyperthermia and imaging properties of the prepared nanoparticles were investigated and compared to the commercial nanoparticles. One-dimensional magnetic particle imaging indicated the good imaging resolution of our nanoparticles. Under the application of a magnetic field of frequency 614.4 kHz and strength 9.5 kA/m, nanoparticles generated heat with an SLP of 216.18 W/g, which is much higher than that of BNF (14 W/g). Thus, the prepared nanoparticles show promise as a novel dual-functional magnetic nanomaterial, enabling both high performance for hyperthermia and imaging functionality for diagnostic and therapeutic processes. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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17 pages, 2519 KiB

Open AccessArticle

Evaluation of Physicochemical Properties of Amphiphilic 1,4-Dihydropyridines and Preparation of Magnetoliposomes

by Oksana Petrichenko, Aiva Plotniece, Karlis Pajuste, Martins Rucins, Pavels Dimitrijevs, Arkadij Sobolev, Einars Sprugis and Andrejs Cēbers

Nanomaterials 2021, 11(3), 593; https://doi.org/10.3390/nano11030593 - 27 Feb 2021

Cited by 6 | Viewed by 2440

Abstract

This study was focused on the estimation of the targeted modification of 1,4-DHP core with (1) different alkyl chain lengths at 3,5-ester moieties of 1,4-DHP (C₁₂, C₁₄ and C₁₆); (2) N-substituent at position 1 of 1,4-DHP (N-H or [...] Read more.

This study was focused on the estimation of the targeted modification of 1,4-DHP core with (1) different alkyl chain lengths at 3,5-ester moieties of 1,4-DHP (C₁₂, C₁₄ and C₁₆); (2) N-substituent at position 1 of 1,4-DHP (N-H or N-CH₃); (3) substituents of pyridinium moieties at positions 2 and 6 of 1,4-DHP (H, 4-CN and 3-Ph); (4) substituent at position 4 of 1,4-DHP (phenyl and napthyl) on physicochemical properties of the entire molecules and on the characteristics of the obtained magnetoliposomes formed by them. It was shown that thermal behavior of the tested 1,4-DHP amphiphiles was related to the alkyl chains length, the elongation of which decreased their transition temperatures. The properties of 1,4-DHP amphiphile monolayers and their polar head areas were determined. The packing parameters of amphiphiles were in the 0.43–0.55 range. It was demonstrated that the structure of 1,4-DHPs affected the physicochemical properties of compounds. “Empty” liposomes and magnetoliposomes were prepared from selected 1,4-DHP amphiphiles. It was shown that the variation of alkyl chains length or the change of substituents at positions 4 of 1,4-DHP did not show a significant influence on properties of liposomes. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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14 pages, 4602 KiB

Open AccessArticle

Inactivation of Bacteria Using Bioactive Nanoparticles and Alternating Magnetic Fields

by Vitalij Novickij, Ramunė Stanevičienė, Rūta Gruškienė, Kazimieras Badokas, Juliana Lukša, Jolanta Sereikaitė, Kęstutis Mažeika, Nikolaj Višniakov, Jurij Novickij and Elena Servienė

Nanomaterials 2021, 11(2), 342; https://doi.org/10.3390/nano11020342 - 29 Jan 2021

Cited by 6 | Viewed by 2878

Abstract

Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefore, food safety and processing remain a priority to control and minimize these risks. In this work, nisin-loaded magnetic nanoparticles were used and activated by alternating 10 and 125 mT (peak [...] Read more.

Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefore, food safety and processing remain a priority to control and minimize these risks. In this work, nisin-loaded magnetic nanoparticles were used and activated by alternating 10 and 125 mT (peak to peak) magnetic fields (AMFs) for biocontrol of bacteria Listeria innocua, a suitable model to study the inactivation of common foodborne pathogen L. monocytogenes. It was shown that L. innocua features high resistance to nisin-based bioactive nanoparticles, however, application of AMFs (15 and 30 min exposure) significantly potentiates the treatment resulting in considerable log reduction of viable cells. The morphological changes and the resulting cellular damage, which was induced by the synergistic treatment, was confirmed using scanning electron microscopy. The thermal effects were also estimated in the study. The results are useful for the development of new methods for treatment of the drug-resistant foodborne pathogens to minimize the risks of invasive infections. The proposed methodology is a contactless alternative to the currently established pulsed-electric field-based treatment in food processing. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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13 pages, 4477 KiB

Open AccessArticle

Deviation of Trypsin Activity Using Peptide Conformational Imprints

by Kiran Reddy Kanubaddi, Pei-Yu Huang, Ya-Lin Chang, Cheng Hsin Wu, Wei Li, Ranjith Kumar Kankala, Dar-Fu Tai and Chia-Hung Lee

Nanomaterials 2021, 11(2), 334; https://doi.org/10.3390/nano11020334 - 27 Jan 2021

Cited by 4 | Viewed by 2900

Abstract

In this study, a methodology utilizing peptide conformational imprints (PCIs) as a tool to specifically immobilize porcine pancreatic alpha-trypsin (PPT) at a targeted position is demonstrated. Owing to the fabrication of segment-mediated PCIs on the magnetic particles (PCIMPs), elegant cavities complementary to the [...] Read more.

In this study, a methodology utilizing peptide conformational imprints (PCIs) as a tool to specifically immobilize porcine pancreatic alpha-trypsin (PPT) at a targeted position is demonstrated. Owing to the fabrication of segment-mediated PCIs on the magnetic particles (PCIMPs), elegant cavities complementary to the PPT structure are constructed. Based on the sequence on targeted PPT, the individual region of the enzyme is trapped with different template-derived PCIMPs to show certain types of inhibition. Upon hydrolysis, N-benzoyl-L-arginine ethyl ester (BAEE) is employed to assess the hydrolytic activity of PCIMPs bound to the trypsin using high-performance liquid chromatography (HPLC) analysis. Further, the kinetic data of four different PCIMPs are compared. As a result, the PCIMPs presented non-competitive inhibition toward trypsin, according to the Lineweaver-Burk plot. Further, the kinetic analysis confirmed that the best parameters of PPT/PCIMPs ^233–245+G were V_max = 1.47 × 10⁻³ mM s⁻¹, K_m = 0.42 mM, k_cat = 1.16 s⁻¹, and k_cat/K_m = 2.79 mM⁻¹ s⁻¹. As PPT is bound tightly to the correct position, its catalytic activities could be sustained. Additionally, our findings stated that the immobilized PPT could maintain stable activity even after four successive cycles. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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14 pages, 5220 KiB

Open AccessArticle

Determination of Cobalt Spin-Diffusion Length in Co/Cu Multilayered Heterojunction Nanocylinders Based on Valet–Fert Model

by Saeko Mizoguchi, Masamitsu Hayashida and Takeshi Ohgai

Nanomaterials 2021, 11(1), 218; https://doi.org/10.3390/nano11010218 - 15 Jan 2021

Cited by 5 | Viewed by 2709

Abstract

Anodized aluminum oxide (AAO) nanochannels of diameter, D, of ~50 nm and length, L, of ~60 µm (L/D: approx. 1200 in the aspect ratio), were synthesized and applied as an electrode for the electrochemical growth of Co/Cu [...] Read more.

Anodized aluminum oxide (AAO) nanochannels of diameter, D, of ~50 nm and length, L, of ~60 µm (L/D: approx. 1200 in the aspect ratio), were synthesized and applied as an electrode for the electrochemical growth of Co/Cu multilayered heterojunction nanocylinders. We synthesized numerous Co/Cu multilayered nanocylinders by applying a rectangular pulsed potential deposition method. The Co layer thickness, t_Co, ranged from ~8 to 27 nm, and it strongly depended on the pulsed-potential condition for Co layers, E_Co. The Cu layer thickness, t_Cu, was kept at less than 4 nm regardless of E_Co. We applied an electrochemical in situ contact technique to connect a Co/Cu multilayered nanocylinder with a sputter-deposited Au thin layer. Current perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ~23% in a Co/Cu multilayered nanocylinder with ~4760 Co/Cu bilayers (t_Cu: 4 nm and t_Co: 8.6 nm). With a decrease in t_Co, (ΔR/R_p)⁻¹ was linearly reduced based on the Valet–Fert equation under the condition of t_F > l_F^sf and t_N < l_N^sf. The cobalt spin-diffusion length, l_Co^sf, was estimated to be ~12.5 nm. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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11 pages, 5267 KiB

Open AccessEditor’s ChoiceArticle

Magnetic Imaging of Encapsulated Superparamagnetic Nanoparticles by Data Fusion of Magnetic Force Microscopy and Atomic Force Microscopy Signals for Correction of Topographic Crosstalk

by Marc Fuhrmann, Anna Musyanovych, Ronald Thoelen, Sibylle von Bomhard and Hildegard Möbius

Nanomaterials 2020, 10(12), 2486; https://doi.org/10.3390/nano10122486 - 11 Dec 2020

Cited by 9 | Viewed by 2637

Abstract

Encapsulated magnetic nanoparticles are of increasing interest for biomedical applications. However, up to now, it is still not possible to characterize their localized magnetic properties within the capsules. Magnetic Force Microscopy (MFM) has proved to be a suitable technique to image magnetic nanoparticles [...] Read more.

Encapsulated magnetic nanoparticles are of increasing interest for biomedical applications. However, up to now, it is still not possible to characterize their localized magnetic properties within the capsules. Magnetic Force Microscopy (MFM) has proved to be a suitable technique to image magnetic nanoparticles at ambient conditions revealing information about the spatial distribution and the magnetic properties of the nanoparticles simultaneously. However, MFM measurements on magnetic nanoparticles lead to falsifications of the magnetic MFM signal due to the topographic crosstalk. The origin of the topographic crosstalk in MFM has been proven to be capacitive coupling effects due to distance change between the substrate and tip measuring above the nanoparticle. In this paper, we present data fusion of the topography measurements of Atomic Force Microscopy (AFM) and the phase image of MFM measurements in combination with the theory of capacitive coupling in order to eliminate the topographic crosstalk in the phase image. This method offers a novel approach for the magnetic visualization of encapsulated magnetic nanoparticles. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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13 pages, 3363 KiB

Open AccessArticle

Coating Effect on the ¹H—NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles

by Francesca Brero, Martina Basini, Matteo Avolio, Francesco Orsini, Paolo Arosio, Claudio Sangregorio, Claudia Innocenti, Andrea Guerrini, Joanna Boucard, Eléna Ishow, Marc Lecouvey, Jérome Fresnais, Lenaic Lartigue and Alessandro Lascialfari

Nanomaterials 2020, 10(9), 1660; https://doi.org/10.3390/nano10091660 - 24 Aug 2020

Cited by 10 | Viewed by 3539

Abstract

We present a ¹H Nuclear Magnetic Resonance (NMR) relaxometry experimental investigation of two series of magnetic nanoparticles, constituted of a maghemite core with a mean diameter d_TEM = 17 ± 2.5 nm and 8 ± 0.4 nm, respectively, and coated with [...] Read more.

We present a ¹H Nuclear Magnetic Resonance (NMR) relaxometry experimental investigation of two series of magnetic nanoparticles, constituted of a maghemite core with a mean diameter d_TEM = 17 ± 2.5 nm and 8 ± 0.4 nm, respectively, and coated with four different negative polyelectrolytes. A full structural, morpho-dimensional and magnetic characterization was performed by means of Transmission Electron Microscopy, Atomic Force Microscopy and DC magnetometry. The magnetization curves showed that the investigated nanoparticles displayed a different approach to the saturation depending on the coatings, the less steep ones being those of the two samples coated with P(MAA-stat-MAPEG), suggesting the possibility of slightly different local magnetic disorders induced by the presence of the various polyelectrolytes on the particles’ surface. For each series, ¹H NMR relaxivities were found to depend very slightly on the surface coating. We observed a higher transverse nuclear relaxivity, r₂, at all investigated frequencies (10 kHz ≤ ν_L ≤ 60 MHz) for the larger diameter series, and a very different frequency behavior for the longitudinal nuclear relaxivity, r₁, between the two series. In particular, the first one (d_TEM = 17 nm) displayed an anomalous increase of r₁ toward the lowest frequencies, possibly due to high magnetic anisotropy together with spin disorder effects. The other series (d_TEM = 8 nm) displayed a r₁ vs. ν_L behavior that can be described by the Roch’s heuristic model. The fitting procedure provided the distance of the minimum approach and the value of the Néel reversal time (τ ≈ 3.5 ÷ 3.9·10⁻⁹ s) at room temperature, confirming the superparamagnetic nature of these compounds. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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15 pages, 2023 KiB

Open AccessArticle

Application of Magnetosomes in Magnetic Hyperthermia

by Nikolai A. Usov and Elizaveta M. Gubanova

Nanomaterials 2020, 10(7), 1320; https://doi.org/10.3390/nano10071320 - 5 Jul 2020

Cited by 30 | Viewed by 3060

Abstract

Nanoparticles, specifically magnetosomes, synthesized in nature by magnetotactic bacteria, are very promising to be usedin magnetic hyperthermia in cancer treatment. In this work, using the solution of the stochastic Landau–Lifshitz equation, we calculate the specific absorption rate (SAR) in an alternating (AC) magnetic [...] Read more.

Nanoparticles, specifically magnetosomes, synthesized in nature by magnetotactic bacteria, are very promising to be usedin magnetic hyperthermia in cancer treatment. In this work, using the solution of the stochastic Landau–Lifshitz equation, we calculate the specific absorption rate (SAR) in an alternating (AC) magnetic field of assemblies of magnetosome chains depending on the particle size D, the distance between particles in a chain a, and the angle of the applied magnetic field with respect to the chain axis. The dependence of SAR on the a/D ratio is shown to have a bell-shaped form with a pronounced maximum. For a dilute oriented chain assembly with optimally chosen a/D ratio, a strong magneto-dipole interaction between the chain particles leads to an almost rectangular hysteresis loop, and to large SAR values in the order of 400–450 W/g at moderate frequencies f = 300 kHz and small magnetic field amplitudes H₀ = 50–100 Oe. The maximum SAR value only weakly depends on the diameter of the nanoparticles and the length of the chain. However, a significant decrease in SAR occurs in a dense chain assembly due to the strong magneto-dipole interaction of nanoparticles of different chains. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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15 pages, 6476 KiB

Open AccessArticle

Room Temperature Magnetic Memory Effect in Cluster-Glassy Fe-Doped NiO Nanoparticles

by Ashish Chhaganlal Gandhi, Tai-Yue Li, B. Vijaya Kumar, P. Muralidhar Reddy, Jen-Chih Peng, Chun-Ming Wu and Sheng Yun Wu

Nanomaterials 2020, 10(7), 1318; https://doi.org/10.3390/nano10071318 - 4 Jul 2020

Cited by 13 | Viewed by 3601

Abstract

The Fe-doped NiO nanoparticles that were synthesized using a co-precipitation method are characterized by enhanced room-temperature ferromagnetic property evident from magnetic measurements. Neutron powder diffraction experiments suggested an increment of the magnetic moment of 3d ions in the nanoparticles as a function [...] Read more.

The Fe-doped NiO nanoparticles that were synthesized using a co-precipitation method are characterized by enhanced room-temperature ferromagnetic property evident from magnetic measurements. Neutron powder diffraction experiments suggested an increment of the magnetic moment of 3d ions in the nanoparticles as a function of Fe-concentration. The temperature, time, and field-dependent magnetization measurements show that the effect of Fe-doping in NiO has enhanced the intraparticle interactions due to formed defect clusters. The intraparticle interactions are proposed to bring additional magnetic anisotropy energy barriers that affect the overall magnetic moment relaxation process and emerging as room temperature magnetic memory. The outcome of this study is attractive for the future development of the room temperature ferromagnetic oxide system to facilitate the integration of spintronic devices and understanding of their fundamental physics. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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11 pages, 1509 KiB

Open AccessArticle

Magnetocrystalline and Surface Anisotropy in CoFe₂O₄ Nanoparticles

by Alexander Omelyanchik, María Salvador, Franco D’Orazio, Valentina Mameli, Carla Cannas, Dino Fiorani, Anna Musinu, Montserrat Rivas, Valeria Rodionova, Gaspare Varvaro and Davide Peddis

Nanomaterials 2020, 10(7), 1288; https://doi.org/10.3390/nano10071288 - 30 Jun 2020

Cited by 27 | Viewed by 4027

Abstract

The effect of the annealing temperature T_ann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe₂O₄/SiO₂), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. [...] Read more.

The effect of the annealing temperature T_ann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe₂O₄/SiO₂), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing T_ann from 700 to 900 °C. The effective magnetic anisotropy constant (K_eff) increases with decreasing T_ann, due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, K_eff is much larger (1.7 × 10⁶ J/m³) than that of the 15% w/w sample (7.5 × 10⁵ J/m³) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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19 pages, 5218 KiB

Open AccessArticle

Biocompatible Magnetic Fluids of Co-Doped Iron Oxide Nanoparticles with Tunable Magnetic Properties

by Silvio Dutz, Norbert Buske, Joachim Landers, Christine Gräfe, Heiko Wende and Joachim H. Clement

Nanomaterials 2020, 10(6), 1019; https://doi.org/10.3390/nano10061019 - 27 May 2020

Cited by 50 | Viewed by 5221

Abstract

Magnetite (Fe₃O₄) particles with a diameter around 10 nm have a very low coercivity (H_c) and relative remnant magnetization (M_r/M_s), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe₂ [...] Read more.

Magnetite (Fe₃O₄) particles with a diameter around 10 nm have a very low coercivity (H_c) and relative remnant magnetization (M_r/M_s), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe₂O₄) particles of the same size have a very high H_c and M_r/M_s, which is magnetically too hard to obtain suitable specific heating power (SHP) in hyperthermia. For the optimization of the magnetic properties, the Fe²⁺ ions of magnetite were substituted by Co²⁺ step by step, which results in a Co doped iron oxide inverse spinel with an adjustable Fe²⁺ substitution degree in the full range of pure iron oxide up to pure cobalt ferrite. The obtained magnetic nanoparticles were characterized regarding their structural and magnetic properties as well as their cell toxicity. The pure iron oxide particles showed an average size of 8 nm, which increased up to 12 nm for the cobalt ferrite. For ferrofluids containing the prepared particles, only a limited dependence of H_c and M_r/M_s on the Co content in the particles was found, which confirms a stable dispersion of the particles within the ferrofluid. For dry particles, a strong correlation between the Co content and the resulting H_c and M_r/M_s was detected. For small substitution degrees, only a slight increase in H_c was found for the increasing Co content, whereas for a substitution of more than 10% of the Fe atoms by Co, a strong linear increase in H_c and M_r/M_s was obtained. Mössbauer spectroscopy revealed predominantly Fe³⁺ in all samples, while also verifying an ordered magnetic structure with a low to moderate surface spin canting. Relative spectral areas of Mössbauer subspectra indicated a mainly random distribution of Co²⁺ ions rather than the more pronounced octahedral site-preference of bulk CoFe₂O₄. Cell vitality studies confirmed no increased toxicity of the Co-doped iron oxide nanoparticles compared to the pure iron oxide ones. Magnetic heating performance was confirmed to be a function of coercivity as well. The here presented non-toxic magnetic nanoparticle system enables the tuning of the magnetic properties of the particles without a remarkable change in particles size. The found heating performance is suitable for magnetic hyperthermia application. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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17 pages, 4369 KiB

Open AccessFeature PaperArticle

Influence of Experimental Parameters of a Continuous Flow Process on the Properties of Very Small Iron Oxide Nanoparticles (VSION) Designed for T₁-Weighted Magnetic Resonance Imaging (MRI)

by Thomas Vangijzegem, Dimitri Stanicki, Adriano Panepinto, Vlad Socoliuc, Ladislau Vekas, Robert N. Muller and Sophie Laurent

Nanomaterials 2020, 10(4), 757; https://doi.org/10.3390/nano10040757 - 15 Apr 2020

Cited by 21 | Viewed by 3447

Abstract

This study reports the development of a continuous flow process enabling the synthesis of very small iron oxide nanoparticles (VSION) intended for T₁-weighted magnetic resonance imaging (MRI). The influence of parameters, such as the concentration/nature of surfactants, temperature, pressure and the [...] Read more.

This study reports the development of a continuous flow process enabling the synthesis of very small iron oxide nanoparticles (VSION) intended for T₁-weighted magnetic resonance imaging (MRI). The influence of parameters, such as the concentration/nature of surfactants, temperature, pressure and the residence time on the thermal decomposition of iron(III) acetylacetonate in organic media was evaluated. As observed by transmission electron microscopy (TEM), the diameter of the resulting nanoparticle remains constant when modifying the residence time. However, significant differences were observed in the magnetic and relaxometric studies. This continuous flow experimental setup allowed the production of VSION with high flow rates (up to 2 mL·min⁻¹), demonstrating the efficacy of such process compared to conventional batch procedure for the scale-up production of VSION. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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21 pages, 7907 KiB

Open AccessArticle

Synthesis of Magnetic Ferrite Nanoparticles with High Hyperthermia Performance via a Controlled Co-Precipitation Method

by Mohamed S. A. Darwish, Hohyeon Kim, Hwangjae Lee, Chiseon Ryu, Jae Young Lee and Jungwon Yoon

Nanomaterials 2019, 9(8), 1176; https://doi.org/10.3390/nano9081176 - 16 Aug 2019

Cited by 102 | Viewed by 7061

Abstract

Magnetic nanoparticles (MNPs) that exhibit high specific loss power (SLP) at lower metal content are highly desirable for hyperthermia applications. The conventional co-precipitation process has been widely employed for the synthesis of magnetic nanoparticles. However, their hyperthermia performance is often insufficient, which is [...] Read more.

Magnetic nanoparticles (MNPs) that exhibit high specific loss power (SLP) at lower metal content are highly desirable for hyperthermia applications. The conventional co-precipitation process has been widely employed for the synthesis of magnetic nanoparticles. However, their hyperthermia performance is often insufficient, which is considered as the main challenge to the development of practicable cancer treatments. In particular, ferrite MNPs have unique properties, such as a strong magnetocrystalline anisotropy, high coercivity, and moderate saturation magnetization, however their hyperthermia performance needs to be further improved. In this study, cobalt ferrite (CoFe₂O₄) and zinc cobalt ferrite nanoparticles (ZnCoFe₂O₄) were prepared to achieve high SLP values by modifying the conventional co-precipitation method. Our modified method, which allows for precursor material compositions (molar ratio of Fe⁺³:Fe⁺²:Co⁺²/Zn⁺² of 3:2:1), is a simple, environmentally friendly, and low temperature process carried out in air at a maximum temperature of 60 °C, without the need for oxidizing or coating agents. The particles produced were characterized using multiple techniques, such as X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV–Vis spectroscopy), and a vibrating sample magnetometer (VSM). SLP values of the prepared nanoparticles were carefully evaluated as a function of time, magnetic field strength (30, 40, and 50 kA m⁻¹), and the viscosity of the medium (water and glycerol), and compared to commercial magnetic nanoparticle materials under the same conditions. The cytotoxicity of the prepared nanoparticles by in vitro culture with NIH-3T3 fibroblasts exhibited good cytocompatibility up to 0.5 mg/mL. The safety limit of magnetic field parameters for SLP was tested. It did not exceed the 5 × 10⁹ Am⁻¹ s⁻¹ threshold. A saturation temperature of 45 °C could be achieved. These nanoparticles, with minimal metal content, can ideally be used for in vivo hyperthermia applications, such as cancer treatments. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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12 pages, 5518 KiB

Open AccessArticle

Magnetic Nanoparticles Functionalized Few-Mode-Fiber-Based Plasmonic Vector Magnetometer

by Yaofei Chen, Weiting Sun, Yaxin Zhang, Guishi Liu, Yunhan Luo, Jiangli Dong, Yongchun Zhong, Wenguo Zhu, Jianhui Yu and Zhe Chen

Nanomaterials 2019, 9(5), 785; https://doi.org/10.3390/nano9050785 - 22 May 2019

Cited by 46 | Viewed by 4325

Abstract

In this work, we demonstrate a highly-sensitive vector magnetometer based on a few-mode-fiber-based surface plasmon resonance (SPR) sensor functionalized by magnetic nanoparticles (MNPs) in liquid. To fabricate the sensor, a few-mode fiber is side-polished and coated with a gold film, forming an SPR [...] Read more.

In this work, we demonstrate a highly-sensitive vector magnetometer based on a few-mode-fiber-based surface plasmon resonance (SPR) sensor functionalized by magnetic nanoparticles (MNPs) in liquid. To fabricate the sensor, a few-mode fiber is side-polished and coated with a gold film, forming an SPR sensor that is highly sensitive to the surrounding refractive index. The vector magnetometer operates based on the mechanism whereby the intensity and orientation of an external magnetic field alters the anisotropic aggregation of the MNPs and thus the refractive index around the fiber SPR device. This, in turn, shifts the resonance wavelength of the surface plasmon. Experimental results show the proposed sensor is very sensitive to magnetic-field intensity and orientation (0.692 nm/Oe and −11.917 nm/°, respectively). These remarkable sensitivities to both magnetic-field intensity and orientation mean that the proposed sensor can be used in applications to detect weak magnetic-field vectors. Full article

(This article belongs to the Special Issue Applications and Properties of Magnetic Nanoparticles)

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