Rattle‐Type Fe3O4@SiO2 Hollow Mesoporous Spheres as Carriers for Drug Delivery

Rattle‐type Fe₃O₄@SiO₂ hollow mesoporous spheres with different particle sizes, different mesoporous shell thicknesses, and different levels of Fe₃O₄ content are prepared by using carbon spheres as templates. The effects of particle size and concentration of Fe₃O₄@SiO₂ hollow mesoporous spheres on cell uptake and their in vitro cytotoxicity to HeLa cells are evaluated. The spheres exhibit relatively fast cell uptake. Concentrations of up to 150 µg mL^?1 show no cytotoxicity, whereas a concentration of 200 µg mL^?1 shows a small amount of cytotoxicity after 48 h of incubation. Doxorubicin hydrochloride (DOX), an anticancer drug, is loaded into the Fe₃O₄@SiO₂ hollow mesoporous spheres, and the DOX‐loaded spheres exhibit a somewhat higher cytotoxicity than free DOX. These results indicate the potential of Fe₃O₄@SiO₂ hollow mesoporous spheres for drug loading and delivery into cancer cells to induce cell death.     

Design of Multifunctional Fluorescent Hybrid Materials Based on SiO2 Materials and Core–Shell Fe3O4@SiO2 Nanoparticles for Metal Ion Sensing

Hybrid fluorescent materials constructed from organic chelating fluorescent probes and inorganic solid supports by covalent interactions are a special type of hybrid sensing platform that has gained much interest in the context of metal ion sensing applications owing to their excellent advantages, recyclability, and solubility/dispersibility in particular, as compared with single organic fluorescent molecules. In recent decades, SiO₂ materials and core–shell Fe₃O₄@SiO₂ nanoparticles have become important inorganic solid materials and have been used as inorganic solid supports to hybridize with organic fluorescent receptors, resulting in multifunctional fluorescent hybrid systems for potential applications in sensing and related research fields. Therefore, recent progress in various fluorescent‐group‐functionalized SiO₂ materials is reviewed, with a focus on mesoporous silica nanoparticles and core–shell Fe₃O₄@SiO₂ nanoparticles, as interesting fluorescent organic–inorganic hybrid materials for sensing applications toward essential and toxic metal ions. Selective examples of other types of silica/silicon materials, such as periodic mesoporous organosilicas, solid SiO₂ nanoparticles, fibrous silica spheres, silica nanowires, silica nanotubes, and silica hollow microspheres, are also mentioned. Finally, relevant perspectives of metal‐ion‐sensing‐oriented silica‐fluorescent probe hybrid materials are provided.     

Fabrication of biosensor based on core–shell and large void structured magnetic mesoporous microspheres immobilized with laccase for dopamine detection

The Fe₃O₄@SiO₂@vmSiO₂ microspheres with ordered mesochannels and large inter-lamellar void were successfully prepared through stepwise solution-phase interface deposition. Fe₃O₄ nanoparticles were coated with SiO₂ via the Stöber method, and they were further coated with mesoporous SiO₂ using aggregation of cetyltrimethylammonium chloride as template to prepare Fe₃O₄@SiO₂@vmSiO₂. The Fe₃O₄@SiO₂@vmSiO₂ microspheres show a well-defined core–shell structure with high magnetization (~ 30.9 emu g^?1), ordered mesochannel (~ 6.8 nm in diameter), and inter-lamellar void (~ 30 nm). Laccase (LAC) was immobilized on a modified Fe₃O₄@SiO₂@vmSiO₂ microsphere by covalent attachment and stabilized onto the glassy carbon electrode (GCE) surface (Fe₃O₄@SiO₂@vmSiO₂-LAC/GCE) in the fabrication of novel immobilized LAC biosensors for monitoring dopamine (DA). The electrochemical properties of the biosensor were investigated with electrochemical impedance spectroscopy and cyclic voltammetry. The immobilized LAC biosensor possesses good DA electrocatalytic activity with a linear range of 1.5–75 μmol L^?1 and low detection limit of 0.177 μmol L^?1 and shows strong anti-interference ability and excellent selective determination of DA that coexists with ascorbic acid. The immobilized LAC biosensor was also used to detect DA in pharmaceutical injection. The recoveries of 98.7–100.5% were obtained for the samples, which illustrate great potential for practical application.     

Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe₃O₄–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe₃O₄ (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe₃O₄ NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe₃O₄ NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe₃O₄ NPs with inverse spinel phase were formed. The results of VSM imply that the Fe₃O₄–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe₃O₄ NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.     

Biosynthesis of mesoporous organic–inorganic hybrid Fe2O3 with high photocatalytic activity

A very simple approach with yeast cells as a biotemplate was proposed to synthesize a mesoporous hybrid Fe₂O₃ photocatalyst. The mesoporous structure of the resultant samples was characterized by BET, N₂ adsorption–desorption isotherms (NADI) and transmission electron microscopy (TEM). The chemical bond linkages in hybrid Fe₂O₃ samples were confirmed by Fourier transform infrared spectroscopy (FT–IR). The catalytic activities of mesoporous hybrid Fe₂O₃ on degradation of methyl orange were investigated under UV-light irradiation. The hybrid Fe₂O₃ (yeast cell amount is 0.6 g) samples dried at 80 °C and calcined at 300 °C exhibit high surface area and photocatalytic activity.     

Synthesis and characterization of core–shell magnetic molecularly imprinted polymer nanoparticles for selective extraction of tizanidine in human plasma

In this study, simple, effective and general processes were used for the synthesis of a new nano-molecularly imprinted polymers (MIPs) layer on magnetic Fe₃O₄ nanoparticles (NPs) with uniform core–shell structure by combining surface imprinting and nanotechniques. The first step for the synthesis of magnetic NPs was co-precipitation of Fe²⁺ and Fe³⁺ in an ammonia solution. Then, an SiO₂ shell was coated on the magnetic core with the Stöber method. Subsequently, the C=C groups were grafted onto the silica-modified Fe₃O₄ surface by 3-(trimethoxysilyl) propyl methacrylate. Finally, MIPs films were formed on the surface of Fe₃O₄@SiO₂ by the copolymerization of C=C end groups with methacrylic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker), 2,2-azobisisobutyronitrile (initiator) and tizanidine (template molecule). The products were characterized using techniques that included Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), UV spectrophotometry, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Measurement of tizanidine through use of the core–shell magnetic molecularly imprinted polymers nanoparticles (MMIPs-NPs) in human plasma samples compared to the paracetamol showed that the synthesized nanosized MMIP for tizanidine has acted selectively.     

Magnetic core‐shell Fe3O4@TiO2 nanocomposites for broad spectrum antibacterial applications

The authors have synthesised a core‐shell Fe₃O₄@TiO₂ nanocomposite consisting of Fe₃O₄ as a magnetic core, and TiO₂ as its external shell. The TiO₂ shell is primarily intended for use as a biocompatible and antimicrobial carrier for drug delivery and possible other applications such as wastewater remediation purposes because of its known antibacterial and photocatalytic properties. The magnetic core enables quick and easy concentration and separation of nanoparticles. The magnetite nanoparticles were synthesized by a hydrothermal route using ferric chloride as a single‐source precursor. The magnetite nanoparticles were then coated with titanium dioxide using titanium butoxide as a precursor. The core‐shell Fe₃O₄@TiO₂ nanostructure particles were characterized by XRD, UV spectroscopy, and FT‐IR, TEM, and VSM techniques. The saturation magnetization of Fe₃O₄ nanoparticles was significantly reduced from 74.2 to 13.7 emu/g after the TiO₂ coating. The antibacterial studies of magnetic nanoparticles and the titania‐coated magnetic nanocomposite were carried out against gram+ve, and gram–ve bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Shigella flexneri , Escherichia coli, and Salmonella typhi) using well diffusion technique. The inhibition zone for E. coli (17 mm after 24 h) was higher than the other bacterial strains; nevertheless, both the uncoated and TiO₂‐coated magnetite nanocomposites showed admirable antibacterial activity against each of the above bacterial strains.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.     

Bactericidal effect of blue LED light irradiated TiO2/Fe3O4 particles on fish pathogen in seawater

This study uses blue LED light (λ_max = 475 nm) activated TiO₂/Fe₃O₄ particles to evaluate the particles' photocatalytic activity efficiency and bactericidal effects in seawater of variable salinities. Different TiO₂ to Fe₃O₄ mole ratios have been synthesized using sol-gel method. The synthesized particles contain mainly anatase TiO₂, Fe₃O₄ and FeTiO₃. The study has identified TiO₂/Fe₃O₄'s bactericidal effect to marine fish pathogen (Photobacterium damselae subsp. piscicida BCRC17065) in seawater. The SEM photo reveals the surface destruction in bacteria incubated with blue LED irradiated TiO₂/Fe₃O₄. The result of this study indicates that 1) TiO₂/Fe₃O₄ acquires photocatalytic activities in both the freshwater and the seawater via blue LED irradiation, 2) higher photocatalytic activities appear in solutions of higher TiO₂/Fe₃O₄ mole ratio, and 3) photocatalytic activity decreases as salinity increases. These results suggest that the energy saving blue LED light is a feasible light source to activate TiO₂/Fe₃O₄ photocatalytic activities in both freshwater and seawater.     

Controllable synthesis and magnetic properties of Fe3O4 and Fe3O4@SiO2 microspheres

We present a systematic study on the preparation, microstructure, and magnetic properties of Fe₃O₄ microspheres and Fe₃O₄@SiO₂ microspheres. Results showed that Fe₃O₄ microspheres’ diameter can be tuned by Fe³⁺ concentration, whereas their average grain size can be tuned by polyethylene glycol (PEG) 2000 dosage or PEG molecular weight. The magnetic saturation value of Fe₃O₄ microspheres was observed to be dependent on their average grain size, but not the sphere diameter. Fe₃O₄@SiO₂ microspheres with different magnetic saturation values were achieved by adjusting shell thickness. Furthermore, the synthesized Fe₃O₄ and Fe₃O₄@SiO₂ microspheres with high and controllable magnetic saturation value endow them with great application potentials.     

Surfactant assisted synthesis and multifunctional features of Fe3O4@ZnO@SiO2 core–shell nanostructure

In this study, hybrid core–shell magnetic nanostructure comprising Fe₃O₄ core with multiple shells of zinc oxide and silica having well defined morphologies are produced by a simple synthetic approach based on an effective chemical precipitation technique. Semi-solid and hydrophilic poly ethylene glycol was used as the stabilizing agent to control the particle size of the magnetic nanostructures. 1-Hexadecyltrimethyl ammonium chloride was employed as the surfactant to achieve the core–shell nanostructure. The formation of the core–shell nanostructures were confirmed by X-ray diffraction, Fourier transform infra-red spectroscopy and high resolution transmission electron microscopy respectively. We also observed the pronounced ferromagnetic features of ZnO coated Fe₃O₄ core–shell nanostructure that substantiates the magnetization reversal mechanism of the spinel magnetite. The coating of dense SiO₂ on Fe₃O₄@ZnO was found to shift the magnetic behaviour from ferromagnetic to super-paramagnetic even at room temperature. The optical features of the material are observed by UV–Vis Spectrometer and Photoluminescence spectrometer.     

A wrinkle to sub-100 nm yolk/shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe₃O₄) and an inert SiO₂ shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO₂ but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe₃O₄@SiO₂ NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe₃O₄@SiO₂ NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO₂ shell. Under our “standard etching code”, the acid-sensitive Fe₃O₄ core can be perfectly preserved and the SiO₂ shell can be selectively etched away. The mechanism of regulation of SiO₂ etching and acidic etching was investigated.

Open image in new window

     

Different combinations of Fe3O4 microsphere,Polypyrrole and silver as core–shell nanocomposites for adsorption and photocatalytic application

Several core–shell nanocomposites composed of Fe₃O₄ microspheres, Polypyrrole and silver were fabricated here by a series of wet chemical methods. The as-prepared nanocomposites were further used in adsorption and photodegradation of azo dyes. The chemical properties of the products were characterized by a series of techniques and equipment. The adsorption and photocatalytic activities of the obtained core–shell heterostructure were studied by controlled experiments. It was found that Fe₃O₄@PPy nanostructure exhibited the highest removal abilities towards organic dyes in aqueous solution among the as-prepared samples. The final removal ratio is 86.2% and 80.4% for Methyl Orange and Orange II aqueous solutions, respectively. Deposition of Ag nanoparticles was employed here to investigate the transportation and separation of photo-induced charges on the surface or interface of Fe₃O₄@PPy under UV illumination.     

Preparation of magnetite core–shell nanoparticles of Fe3O4 and carbon with aryl sulfonyl acetic acid

High quality Fe₃O₄/carbon core–shells and shell–core nanoparticles have been successfully synthesized by depositing an epitaxial growth of Fe₃O₄ or carbon shell onto carbon or Fe₃O₄ nanocore. By employing the agents such as aryl sulfonyl acetic acid and glucose, Fe₃O₄ and carbon in a nanoscale was prepared from iron aryl sulfonyl acetate and then by the solvothermal reaction of glucose in a reverse microemulsion. The advantages of present approach rely not only on its simplicity, rapidity, and efficiency of the procedure, but also the formation of the controlled core–shell structures as well. It is highly suitable for further applications. Different core–shell structure controls could be attained by careful adjustment of the procedure sequences of decarboxylation and solvothermal reaction. The magnetic studies show that Fe₃O₄/carbon core–shell and shell–core nanoparticles found to be superparamagnetic. The characteristic differences in the core–shell structures would lead to the change of magnetization behaviors of Fe₃O₄ nanoparticles.     

Characterisation of binary (Fe3O4/SiO2) biocompatible nanocomposites as magnetic fluid

This article describes coating of magnetite nanoparticles (NPs) with amorphous silica shells. Controlled co-precipitation technique under N₂ gas was used to prevent undesirable critical oxidation of Fe²⁺. The synthesised Fe₃O₄ NPs were first coated with trisodium citrate to achieve solution stability and then covered by SiO₂ layer using Stober method. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetisation range of 82–96?emu/g and coercivity of 85–120?Oe for particles between 35 and 96?nm, respectively. The best value of specific surface area (41?m²/g) for Fe₃O₄ alone was obtained at 0.9?M NaOH at 750?rpm and it increased to about 81?m²/g for Fe₃O₄/SiO₂ combination. The total thickness and the structure of core–shell was measured and studied by transmission electron microscopy. The average particles size was about 50?nm, indicating the presence of about 15?nm SiO₂ layer. Finally, the stable magnetic fluid contained well-dispersed magnetite-silica nanocomposites which showed monodispersity and fast magnetic response.     

Effect of Carbon Shell on the Structural and Magnetic Properties of Fe3O4 Superparamagnetic Nanoparticles

Carbon-encapsulated iron oxides (Fe₃O₄/C) with a core/shell structure have been successfully synthesized by using a simple two-step hydrothermal method at 180 ^°C. Fe₃O₄ core nanoparticles were prepared by coprecipitation under two conditions. Synthesized nanoparticles were characterized by transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. TEM images and FTIR results prove that carbon coated iron oxide is formed and the estimated size for most of them is below 11 nm, which was consistent with the XRD result. The Williamson–Hall (W–H) method has been used to calculate crystallite sizes and lattice strain based on the peak broadening of the Fe₃O₄ and Fe₃O₄/C nanoparticles. The results of VSM imply that the Fe₃O₄ core and core–shell nanoparticles are superparamagnetic. The saturation magnetization of Fe₃O₄ and Fe₃O₄/C are 49 emu/gr and 40 emu/gr, respectively. The magnetic behaviors reveal that the amorphous carbon shell can decrease the saturation magnetization of Fe₃O₄ nanoparticles due to core–shell interface effects and shielding.     

Preparation,characterization and application of Fe3O4/ZnO core/shell magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized by a co-precipitation method. The phase purity was confirmed by X-ray powder diffraction (XRD) analysis. The crystal size was found to be 10 nm from transmission electron microscopy (TEM). It is evidenced that the surface of Fe₃O₄ MNPs was modified by sodium citrate. The Fe₃O₄/ZnO core/shell MNPs were obtained by coating the MNPs with direct precipitation using zinc acetate and ammonium carbonate. The precursor was firstly dried and then calcined at 350 °C. The antioxidation tests indicated that the core/shell MNPs give better antioxidation than that of the Fe₃O₄ MNPs. The photocatalytic degradation of methyl orange revealed that the core/shell MNPs have higher photocatalytic activity than that of the ZnO nanoparticles. Separation of the core/shell MNPs from the aqueous suspension using a magnet provides an easy way to recycle the core/shell MNPs. After four-time recycling, the photocatalytic degradation percentage of the core/shell MNPs is about 70%.     

Antimicrobial activity of composite nanoparticles consisting of titania photocatalytic shell and nickel ferrite magnetic core

Reverse micelle and hydrolysis have been combined to synthesize composite nanoparticles consisting of anatase–titania photocatalytic shell and nickel ferrite magnetic core. The average particle size of the composite nanoparticles was in the range of 10–15 nm. The photocatalytic shell of titania is responsible for the photocatalytic and anti-microbial activity and nickel ferrite magnetic core is responsible for the magnetic behavior, studied by superconducting quantum interference device. The anatase TiO2 coated NiFe₂O₄ nanoparticles retains the magnetic characteristics of uncoated nanocrystalline nickel ferrites, superparamagnetism (absence of hysteresis, remanence and coercivity at 300 K) and non-saturation of magnetic moments at high field. The magnetic measurements results encourage their application as removable anti-microbial photocatalysts. Bacterial inactivation with UV light in the presence of titania-coated NiFe₂O₄ nanoparticles is faster than the action with UV light alone.     

Facile synthesis of titania-encapsulated magnetites with controlled magnetism and surface morphology

Titania-encapsulated magnetites (A-Fe₃O₄@TiO₂) were facilely fabricated through the modified sol–gel reaction of APTMS-complexed Fe₃O₄ (A-Fe₃O₄) with tetraethyl orthotitanate (TEOT). The magnetism and surface morphology of A-Fe₃O₄@TiO₂ were controlled by adjusting the thickness of titania capsule layer. A-Fe₃O₄@TiO₂ exhibited the superparamagnetic characteristics of negligible remanence and coercity. Thermal analysis of A-Fe₃O₄@TiO₂ showed that the amorphous titania was transformed into crystalline phase at around 440 °C. The core–shell magnetite–titanium nanocomposites can be an attractive candidate for recyclable photocatalysts with magnetite core and/or active Fe₃O₄ electrode materials with buffering TiO₂ capsules.     

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanospheres: preparation and photocatalytic activity

A facile and efficient approach for the fabrication of Fe₃O₄@TiO₂ nanospheres with a good core–shell structure has been demonstrated. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that Fe₃O₄@TiO₂ nanocomposites exhibited high degree of crystallinity, excellent magnetic properties at room temperature. Furthermore, the as-prepared Fe₃O₄@TiO₂ nanocomposites exhibited good photocatalytic activity toward the degradation of Rhodamine B (RhB) solution. Additionally, the recycling experiment of Fe₃O₄@TiO₂ nanocomposites had been done, demonstrating that Fe₃O₄@TiO₂ nanocomposites have high efficiency and stability.