Recent research progress on the preparation and application of magnetic nanospheres

Magnetic-controlled dandelion-like nanocatalytic swarm for targeted biofilm elimination

Infections caused by drug-resistant strains pose a serious threat to human health. Most bacterial infections are related to biofilms. The generation of a bacterial biofilm greatly reduces the antibacterial efficiency of antibiotics and some traditional antibacterial drugs, and it is very important to develop antibacterial drugs to replace antibiotics. Here, encouraged by the promising magnetic control technology of micro/nanorobots, the synergistic antibacterial strategy of a dandelion-like magnetically-controlled multifunctional hierarchical magnetic biomimetic nanozyme, Fe₃O₄@SiO₂@dendritic mesoporous silica@small-Fe₃O₄ nanoparticles (FSDMSsF NPs), was developed to be effective against bacterial biofilms. FSDMSsF NPs showed great magnetic properties and peroxidase-like activities, and could act as catalytic carriers for the production of hydroxyl radicals that are highly toxic to bacteria in a low-concentration H₂O₂ environment, killing planktonic bacteria. The antibacterial rate of FSDMSsF NPs reached 99.5% at a concentration of 200 μg mL^-1. The synergistic antibacterial mechanisms of the mechanical factor and the chemical factor are further discussed. Under time-varying magnetic swarm control, the antibacterial performance of FSDMSsF NPs against bacteria was significantly improved. On this basis, the elimination effect of FSDMSsF NPs on bacterial biofilms is further discussed. The results showed that FSDMSsF NPs could target and eliminate biofilms through complex channels under the control of magnetic fields. In addition, the system could remove biofilms in occlusions by changing the morphology and movement mode of an FSDMSsF NP swarm under magnetic field control. The current work proposes a facile and physical-chemical synergistic strategy for effective antibacterial therapy. FSDMSsF NPs could effectively kill planktonic bacteria and remove stubborn biofilms through magnetic field guidance, achieving thorough antibacterial efficacy, which has great potential in the treatment of drug-resistant bacterial infections.

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

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

Organophilic, Superparamagnetic, and Reversibly Thermoresponsive Silica-Polypeptide Core-Shell Particles

Particles with a superparamagnetic cobalt inner core, silica outer core, and covalently bound homopolypeptide shell were investigated under thermal and magnetic stimuli. The homopolypeptide was poly(ε-carbobenzyloxy-l-lysine), PCBL, which is known to exhibit a thermoreversible coil ⇔ helix transition when dissolved as a pure polymer in m-cresol. Tethering to a core particle did not prevent PCBL from undergoing this conformational transition, as confirmed by dynamic light scattering and optical rotation, but the transition was broadened compared to that of the untethered polymer. The Co@SiO₂-PCBL hybrid particles retained the superparamagnetic properties of the cobalt inner nougat. Indeed, some response remains even after aging for >5 years. The aged PCBL shell also preserved its responsiveness to temperature, although differences in the shape of the size vs temperature transition curve were observed compared to the freshly made particles. A reversible coil ⇔ helix transition for a particle-bound polypeptide in a pure organic solvent is rare. In addition to providing a convenient tool for characterizing coil ⇔ helix transitions for surface-bound polypeptides without interference from pH or the strong ionic forces that dominate behavior in aqueous systems, the Co@SiO₂-PCBL/m-cresol system may prove useful in studies of the effect of shell polymer conformation on colloid interactions. The stability of the magnetic core and polypeptide shell suggest a long shelf life for Co@SiO₂-PCBL, which can, in principle, be deprotected to yield positively charged Co@SiO₂-poly(l-lysine) particles for possible transfection or antimicrobial applications or chained magnetically to produce responsive poly(colloids).

A C-Doped TiO2/Fe3O4 Nanocomposite for Photocatalytic Dye Degradation under Natural Sunlight Irradiation

Magnetically recyclable C-doped TiO2/Fe3O4 (C-TiO2/Fe3O4) nanocomposite was successfully synthesized via a sol–gel method. The synthesized samples were characterized using SEM, energy-dispersive X-ray spectroscopy (EDS), FTIR, and UV-VIS diffuse reflectance spectroscopy (DRS) techniques. The results clearly showed that a C-TiO2/Fe3O4 nanocomposite was produced. The photocatalytic activities of the prepared pristine (TiO2), C-doped TiO2 (C-TiO2) and C-TiO2/Fe3O4 were evaluated by the photodegradation of methyl orange (MO) under natural sunlight. The effect of catalyst loading and MO concentration were studied and optimized. The C-TiO2/Fe3O4 nanocomposite exhibited an excellent photocatalytic activity (99.68%) that was higher than the TiO2 (55.41%) and C-TiO2 (70%) photocatalysts within 150 min. The magnetic nanocomposite could be easily recovered from the treated solution by applying external magnetic field. The C-TiO2/Fe3O4 composite showed excellent photocatalytic performance for four consecutive photocatalytic reactions. Thus, this work could provide a simple method for the mass production of highly photoactive and stable C-TiO2/Fe3O4 photocatalyst for environmental remediation.

Modified Fe3O4 Magnetic Nanoparticle Delivery of CpG Inhibits Tumor Growth and Spontaneous Pulmonary Metastases to Enhance Immunotherapy

As a novel toll-like receptor 9 (TLR9) agonist, synthetic unmethylated cytosine-phosphate-guanine (CpG) oligodeoxynucleotides can stimulate a Th1 immune response and potentially be used as therapeutic agents or vaccine adjuvants for the treatment of cancer. However, some drawbacks of CpG limit their applications, such as rapid elimination by nuclease-mediated degradation and poor cellular uptake. Therefore, repeat high-dose drug administration is required for treatment. In this work, a CpG delivery system based on 3-aminopropyltriethoxysilane (APTES)-modified Fe₃O₄ nanoparticles (FeNPs) was designed and studied for the first time to achieve better bioactivity of CpG. In our results, we designed FeNP-delivered CpG particles (FeNP/CpG) with a small average size of approximately 50 nm by loading CpG into FeNPs. The FeNP/CpG particle delivery system, with enhanced cell uptake of CpG in bone marrow-derived dendritic cells (BMDCs) in vitro and through intratumoral injection, showed significant antitumor ability by stimulating better humoral and cellular immune responses in C26 colon cancer and 4T1 breast cancer xenograft models in vivo over those of free CpG. Moreover, mice treated by FeNP/CpG particles had delayed tumor growth with an inhibitory rate as high as 94.4%. In addition, approximately 50% of the tumors in the C26 model appeared to regress completely. Similarly, there were lower pulmonary metastases and a 69% tumor inhibitory rate in the 4T1 breast cancer tumor model than those in the untreated controls. In addition to their effectiveness, the easy preparation, safety, and high stability of FeNP/CpG particles also make them an attractive antitumor immunotherapy.

Designed Synthesis of Nanostructured Magnetic Hydroxyapatite Based Drug Nanocarrier for Anti-Cancer Drug Delivery toward the Treatment of Human Epidermoid Carcinoma

Superparamagnetic Fe₃O₄ nanoparticles on hydroxyapatite nanorod based nanostructures (Fe₃O₄/HAp) were synthesized using hydrothermal techniques at 180 °C for 12 h and were used as drug delivery nanocarriers for cancer cell therapeutic applications. The synthesized Fe₃O₄/HAp nanocomposites were characterized by X-ray diffraction analysis (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET)-analysis, and vibrating sample magnetometry (VSM). The morphologies of the Fe₃O₄/HAp nanocomposites show 15 nm Fe₃O₄ nanoparticles dispersed in the form of rods. The BET result shows that the synthesized samples have a high specific surface area of 80 m² g-1 with mesoporous structures. Magnetic measurements revealed that the sample has high saturation magnetization of 18 emu/g with low coercivity. The Fe₃O₄/HAp nanocomposites had a large specific surface area (SSA), high mesoporous volume, and good magnetic property, which made it a suitable nanocarrier for targeted drug delivery systems. The chemotherapeutic agent, andrographolide, was used to investigate the drug delivery behavior of the Fe₃O₄/HAp nanocomposites. The human epidermoid skin cancer cells (A431) were used as the model targeting cell lines by treating with andrographolide loaded Fe₃O₄/HAp nanosystems and were further evaluated for their antiproliferative activities and the induction of apoptosis. Also, the present nanocomposite shows better biocompatibility, therefore it can be used as suitable drug vehicle for cancer therapy applications.

ß-Amido Acid Functionalised Superparamagnetic Iron Oxide Nanoparticles as a Novel Carrier for Efficient Delivery of Doxorubicine

Superparamagnetic iron oxide nanoparticles are increasingly used in medical applications due to their unique physical properties. They are useful carriers for delivering antitumour drugs in targeted cancer treatment. In this study, amido acid-functionalised magnetic nanoparticles (AAFMNs) are used as drug-delivery vehicles for doxorubicine as an efficient tool for the treatment of cancer. Magnetic iron oxide nanoparticles were synthesised using a co-precipitation method. The prepared iron oxide nanoparticles were then functionalised with amido acid functional groups. Finally, the synthesised AAFMNs were used for the delivery of doxorubicine. AAFMNs were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and zeta potential. An in vitro-determined hydrodynamic diameter of ∼80 nm suggested their applicability for this purpose. The findings show that AAFMNs are a promising tool for potential magnetic drug delivery.

Virus-Templated Near-Amorphous Iron Oxide Nanotubes

We present a simple synthesis of iron oxide nanotubes, grown under very mild conditions from a solution containing Fe(II) and Fe(III), on rod-shaped tobacco mosaic virus templates. Their well-defined shape and surface chemistry suggest that these robust bionanoparticles are a versatile platform for synthesis of small, thin mineral tubes, which was achieved efficiently. Various characterization tools were used to explore the iron oxide in detail: Electron microscopy (SEM, TEM), magnetometry (SQUID-VSM), diffraction (XRD, TEM-SAED), electron spectroscopies (EELS, EDX, XPS), and X-ray absorption (XANES with EXAFS analysis). They allowed determination of the structure, crystallinity, magnetic properties, and composition of the tubes. The protein surface of the viral templates was crucial to nucleate iron oxide, exhibiting analogies to biomineralization in natural compartments such as ferritin cages.

Design and Utility of Metal/Metal Oxide Nanoparticles Mediated by Thioether End-Functionalized Polymeric Ligands

The past few decades have witnessed significant advances in the development of functionalized metal/metal oxide nanoparticles including those of inorganic noble metals and magnetic materials stabilized by various polymeric ligands. Recent applications of such functionalized nanoparticles, including those in bio-imaging, sensing, catalysis, drug delivery, and other biomedical applications have triggered the need for their facile and reproducible preparation with a better control over their size, shape, and surface chemistry. In this perspective, the multidentate polymer ligands containing functional groups like thiol, thioether, and ester are important surface ligands for designing and synthesizing stable nanoparticles (NPs) of metals or their oxides with reproducibility and high yield. These ligands have offered an unprecedented control over the particle size of both nanoparticles and nanoclusters with enhanced colloidal stability, having tunable solubility in aqueous and organic media, and tunable optical, magnetic, and fluorescent properties. This review summarizes the synthetic methodologies and stability of nanoparticles and fluorescent nanoclusters of metals (Au, Ag, Cu, Pt, and other transition metal oxides) prepared by using thioether based ligands and highlights their applications in bio-imaging, sensing, drug delivery, magnetic resonance imaging (MRI), and catalysis. The future applications of fluorescent metal NPs like thermal gradient optical imaging, single molecule optoelectronics, sensors, and optical components of the detector are also envisaged.

Adsorption and photocatalyst assisted dye removal and bactericidal performance of ZnO/chitosan coating layer

Pure chitosan and its zinc oxide composite coatings were applied on microfibriller cellulose mat (MCM) to prepare chitosan coated microfibriller cellulose (Chi-MCM) and zinc oxide/chitosan coated microfibriller cellulose (ZnO/Chi-MCM), respectively. X-ray diffraction (XRD), and scanning electron microscopy (SEM), were used to characterize the samples in this study. SEM images showed that dense chitosan solutions (3 and 5wt%) made a thick layer over MCM while diluted solution (1wt%) resulted in wrapping of the chitosan over the individual microfibers and avoided the thick layer formation. Removal of an azo dye methyl orange (MO) from aqueous solution using adsorption and combined adsorption with photodegradation activity of the Chi-MCM and ZnO/Chi-MCM were evaluated, respectively. Compared in the absence of UV light, ZnO/Chi-MCM showed faster and higher degree of dye removal by photocatalytic dissociation and adsorption under ultraviolet irradiation. Various parameters including pH of MO solution and its initial concentration were tested for the removal of MO dye. ZnO/Chi-MCM showed maximum adsorption capacity of 42.8mg/g. Antibacterial activities were also evaluated where ZnO/Chi-MCM displayed a remarkable performance inhibiting the Escherichia coli growth.

Combination of magnetic field and surface functionalization for reaching synergistic effects in cellular labeling by magnetic core–shell nanospheres

The joint effect of surface functionalization and an external magnetic field on cellular labeling was studied.

Influence of surface-modified maghemite nanoparticles on in vitro survival of human stem cells

Surface-modified maghemite (γ-Fe2O3) nanoparticles were obtained by using a conventional precipitation method and coated with D-mannose and poly(N,N-dimethylacrylamide). Both the initial and the modified particles were characterized by transmission electron microscopy and dynamic light scattering with regard to morphology, particle size and polydispersity. In vitro survival of human stem cells was then investigated by using the methyl thiazolyl tetrazolium (MTT) assay, which showed that D-mannose- and poly(N,N-dimethylacrylamide)-coated γ-Fe2O3 particles exhibit much lower level of cytotoxicity than the non-coated γ-Fe2O3.

Configuration dependent demagnetizing field in assemblies of interacting magnetic particles

A mean field model is presented for the configuration dependent effective demagnetizing and anisotropy fields in assemblies of exchange decoupled magnetic particles of arbitrary shape which are expressed in terms of the demagnetizing factors of the particles and the volumetric shape containing the assembly. Perpendicularly magnetized two-dimensional (2D) assemblies have been considered, for which it is shown that the demagnetizing field is lower than the continuous thin film. As an example of these 2D systems, arrays of bistable cylindrical nanowires have been characterized by remanence curves as well as ferromagnetic resonance, serving to show the correspondence of these measurements with the model and also to validate the mean field approach. Linear chains of cylinders and spheres have been analyzed, leading to simple expressions to describe the easy axis rotation induced by the interaction field in chains of low aspect ratio cylindrical particles, and the dipolar magnetic anisotropy observed in the linear chain of spheres. These examples serve to underline the dependence on the dipolar interaction field and effective demagnetizing factor of the contributions that arise from the shape of the outer volume.

New forms of superparamagnetic nanoparticles for biomedical applications

Magnetic nanoparticles (MNPs) based on iron oxide, especially magnetite (Fe3O4), have been explored as sensitive probes for magnetic resonance imaging and therapeutic applications. Such application potentials plus the need to achieve high efficiency and sensitivity have motivated the search for new forms of superparamagnetic NPs with additional chemical and physical functionalities. This review summarizes the latest development of high moment MNPs, multifunctional MNPs, and porous hollow MNPs for biosensing, molecular imaging, and drug delivery applications.