Development of poly(vinyl acetate-methylacrylic acid)/chitosan/Fe3O4 nanoparticles for the diagnosis of non-alcoholic steatohepatitis with magnetic resonance imaging

Non-alcoholic steatohepatitis is a burgeoning health problem. To diagnose NASH with magnetic resonance imaging (MRI), an effective contrast agent, a stable suspension of superparamagnetic Fe₃O₄ nanoparticles, were newly developed. The negatively charged Fe₃O₄ nanoparticles were coated with positive chitosan (CS) firstly, and then assembled with poly(vinyl acetate-methylacrylic acid) (P(VAc-MAA)). Transmission electron microscope and dynamic light scattering confirmed that the obtained P(VAc-MAA)/CS/Fe₃O₄ nanoparticles had a spherical or ellipsoidal morphology with an average diameter in the range of 14–20 nm. The superparamagnetic property and spinel structure of the Fe₃O₄ nanoparticles were well preserved due to the protection of the P(VAc-MAA)/CS layers on the surface of the Fe₃O₄ nanoparticles. The in vivo rat experiments confirmed that the P(VAc-MAA)/CS/Fe₃O₄ nanoparticles were an effective contrast agent for MRI to diagnose NASH.     

Preparation of Fe3O4–chitosan nanoparticles used for hyperthermia

The Fe₃O₄–chitosan nanoparticles with core-shell structure have been prepared by crosslinking method. Oleic acid modified Fe₃O₄ nanoparticles were firstly prepared by co-precipitation then chitosan was added to coat on the surface of the Fe₃O₄ nanoparticles by physical absorption. The Fe₃O₄–chitosan nanoparticles were obtained by crosslinking the amino groups on the chitosan using glutaraldehyde. Transmission electron microscopy showed that the Fe₃O₄–chitosan nanoparticles were quasi-spherical with a mean diameter of 10.5 nm. X-ray diffraction pattern and X-ray photoelectron spectra indicated that the magnetic nanoparticles were pure Fe₃O₄ with a cubic inverse spinel structure. The modification using chitosan did not result in a phase change. The binding of chitosan to the Fe₃O₄ nanoparticles was also demonstrated by the measurement of fourier transform infrared spectra and thermogravimetric analysis. Magnetic measurement revealed that the saturation magnetization of the composite nanoparticles was 30.7 emu/g and the nanoparticles were superparamagnetic at room temperature. Furthermore, the inductive heating property of the composite nanoparticles in an alternating current magnetic field was investigated and the results indicated that the heating effect was significant. The Fe₃O₄–chitosan nanoparticles prepared have great potential in hyperthermia.     

Studies of the magnetic field intensity on the synthesis of chitosan-coated magnetite nanocomposites by co-precipitation method

Chitosan-coated magnetite nanocomposites (Fe₃O₄/CS) were prepared under different external magnetic field by co-precipitation method. The effects of the magnetic field intensity on phase composition, morphology and magnetic properties of the Fe₃O₄/CS nanocomposites were investigated by X-ray diffractometer (XRD), Fourier transform infrared analysis (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that the intensity of the magnetic field in the co-precipitation reaction process did not result in the phase composition change of the magnetic chitosan but improved the crystallinity of magnetite. The morphology of Fe₃O₄/CS nanocomposites was greatly changed by the magnetic field. It was varied from random spherical particles to chain-like cluster structure and rod-like cluster structure with the magnetic field intensity increased in the synthetic process. The VSM results indicated that all the products had excellent superparamagnetic properties regardless of the presence or the absence of the magnetic field, and the saturation magnetization values of the Fe₃O₄/CS nanocomposites were significantly improved by the magnetic field.     

Preparation and characterization of novel sinomenine microcapsules for oral controlled drug delivery

Background: Developing a sustained release drug to cure arthritis is needed. Sinomenine (SIN) is abstracted from sinomenium acutum and widely used in the treatment of various rheumatism and arrhythmia with few side effects. The primary aim of this study is to develop SIN microcapsules with polyelectrolyte multilayers for controlled drug release. Method: SIN microcrystals were encapsulated with chitosan, gelatin, and alginate by layer-by-layer technique, such as (gelatin/alginate)₄ and (chitosan/alginate)₆. The size distribution, zeta-potential, stability, and morphology of the microcapsules were characterized by a particle size analyzer, zetasizer, ultraviolet spectroscopy, and transmission electron microscope, respectively. The in vitro controlled release pattern of SIN was studied using a diffusion cell assembly at physiological pH of 6.8 or 1.4. Results: Light stability of these microcapsules was improved after microencapsulation. Compared with release rate of the SIN microcapsules coated by the poly(dimethyldiallyl ammonium chloride)/alginate and gelatin/alginate multilayers, release rate of the SIN microcapsules coated with chitosan/alginate multilayers was fast. Release rate progressively decreased with the increase of chitosan/alginate bilayer number and the decrease of pH value of release medium. Conclusion: These novel SIN microcapsules may be developed into oral controlled drug delivery for rheumatism and arthritis.     

Synthesis of chitosan/poly (ethylene glycol)-modified magnetic nanoparticles for antibiotic delivery and their enhanced anti-biofilm activity in the presence of magnetic field

Biocompatible Fe₃O₄/chitosan (CS)/poly (ethylene glycol) (PEG)/gentamicin (Gent) magnetic nanoparticles, namely Fe₃O₄@PEG-Gent NPs, have been successfully developed for antibiotic delivery. In which, PEG dicarboxylic acid was used to modify Fe₃O₄ NPs for good dispersity as well as offer sufficient carboxyl groups as binding sites. And then the free Gent was facilely loaded onto Fe₃O₄ NPs so as to achieve powerful antibacterial activity via electrostatic interactions. Under acidic condition, the CS and PEG of Fe₃O₄@PEG-Gent were protonated to introduce the positive charge to NPs surface, thus facilitating the contact with negatively charged bacterial cell membrane. What is more, the stretches of CS chains triggered by acidic pH may prevent the antimicrobial efficiency of Gent from weakening. Compared with the free antibiotic, these nanocomposites presented better antimicrobial efficacy against gram-positive bacteria S. aureus under acidic condition. Intriguingly, the confocal laser scanning macroscopy imaging suggested that the anti-biofilm efficacy of nanocomposites was significantly enhanced in the presence of an external magnetic field. Due to the superparamagnetic performance of Fe₃O₄ NPs, these nanocomposites were allowed deeper penetration into a mature biofilm of S. aureus by magnetic field, leading to an effective Gent delivery for eradication of biofilm. The ingenious fabrication of the antibiotic delivery system not only efficiently improved the effectiveness and bioavailability of Gent at acidic media, but also provided an innovative platform to treat bacterial biofilms-associated infection by applying extra environmental factors such as magnetic field.     

Green synthesis of superparamagnetic magnetite nanoparticles: effect of natural surfactant and heat treatment on the magnetic properties

A facile and eco-friendly synthetic approach was employed to synthesize superparamagnetic magnetite (Fe₃O₄) nanoparticles with cubic lattice structure. Zucchini and pomegranate peel-extracts were used as natural stabilizer and surfactant. The X-ray diffraction patterns revealed that the green synthetic technique was successful in formation of highly distributed Fe₃O₄ nanoparticles using both of the above extracts. The infrared (IR) analysis further confirmed the phase formation and the binding of extracts with Fe₃O₄ nanoparticles. Based on UV–Vis analysis, the samples showed the characteristic of surface plasmon resonance in the presence of Fe₃O₄ nanoparticles. The as-synthesized samples were heated at 550 °C for 2 h. It was found that the particles however grew, their sizes remained in nanoscale regime, indicating their thermal stability. The VSM analysis indicated that the as-synthesized samples have a saturation magnetization of 21.4 emu/g (using zucchini peel extract) and 13.3 emu/g (using pomegranate peel extract), which increased respectively to 45.8 emu/g and 38.1 emu/g after the heating process. A negligible coercivity in the samples with the particle sizes of less than 10 nm suggests superparamagnetic behavior of the samples.     

Electromagnetic and microwave absorbing properties of magnetite nanoparticles decorated carbon nanotubes/polyaniline multiphase heterostructures

Magnetite nanoparticles decorated CNTs/PANI multiphase heterostructures were prepared by polymerization of aniline monomer and an additional process of the coprecipitation of Fe²⁺ and Fe³⁺. Scanning electron microscopy and transmission electron microscopy observation indicated that the monodispersed magnetite nanoparticles were uniformly decorated on the surface of CNTs/PANI. The formation of magnetite nanoparticles on CNTs/PANI was mainly through a preferentially position-selective precipitation process. More interestingly, a portion of Fe₃O₄ nanoparticles was found to form core–shell structures with PANI. The effects of different additional amounts of NH₂Fe(SO₄)₂·6H₂O reactant on the magnetic properties and microwave absorbing performances of CNTs/PANI/Fe₃O₄ heterostructures were investigated. The CNTs/PANI/Fe₃O₄ multiphase heterostructures were proved to be superparamagnetic. The microwave absorption measurement showed that the CNTs/PANI/Fe₃O₄ samples under 1.5 g of NH₂Fe(SO₄)₂·6H₂O condition exhibited much more effective absorption performance. These results suggested the novel CNTs/PANI/Fe₃O₄ multiphase heterostructures with PANI as the second phase may be potential candidate for microwave absorption systems.     

A facile route to synthesis of superparamagnetic Fe3O4–PDVB nanoworms

Fe₃O₄–polydivinylbenzene (PDVB) nanoworms were firstly synthesized by precipitation polymerization of divinylbenzene in the presence of oleic acid coated iron oxide nanoparticles. The nanoworms had superparamagnetic properties at room temperature, but ferromagnetism at 5 K. Thermogravimetric analysis curves indicated that in comparison with magnetic nanoparticles, the weight percent of iron oxide in nanoworms was slightly declined due to the formation of Fe₃O₄–PDVB nanocomposites. The superparamagnetic nanoworms could be well dispersed in ethanol, and were capable of easy separation by an external magnetic field. Overall, this provided a valuable methodology for preparation of elongated magnetic nanoparticles with high surface-to-volume ratio, which had potential applications in drug delivery/targeting, magnetic resonance imaging, and nanoprobes for diagnosis and disease treatment.     

Poly(3-hydroxybutyrate)-based hybrid materials with photocatalytic and magnetic properties prepared by electrospinning and electrospraying

Several types of nanostructured hybrid fibrous materials containing poly(3-hydroxybutyrate), nanoparticles from iron oxide (Fe₃O₄) and titanium dioxide (TiO₂), and chitosan or chitosan oligosaccharides (COS) were prepared. The design of the surface of the materials and their magnetic properties were tailored purposefully by conjunction of electrospinning and electrospraying. The surface and bulk morphologies of the obtained nanostructured materials were examined by SEM. Further, the distribution of Fe₃O₄ and TiO₂ nanoparticles was estimated by TEM analyses, as well as their surface chemical composition was determined by XPS. It was found that the simultaneous electrospinning and electrospraying of Fe₃O₄/chitosan or TiO₂/COS dispersions resulted in uniform distribution of the nanoparticles along the length of the fibers, while electrospraying of the mixed Fe₃O₄/TiO₂/chitosan dispersion led to agglomerate formation. Furthermore, the nanostructured hybrid materials preserved the magnetic properties of Fe₃O₄ embedded therein. It was demonstrated that the hybrid materials of different designs displayed excellent photocatalytic activity under UV light irradiation against a model organic contaminant—methylene blue, even after threefold use of the materials.     

Ligand‐Free Fe3O4/CMCS Nanoclusters with Negative Charges for Efficient Structure‐Selective Protein Adsorption

The easy and effective capture of a single protein from a complex mixture is of great significance in proteomics and diagnostics. However, adsorbing nanomaterials are commonly decorated with specific ligands through a complicated and arduous process. Fe₃O₄/carboxymethylated chitosan (Fe₃O₄/CMCS) nanoclusters are developed as a new nonligand modified strategy to selectively capture bovine hemoglogin (BHB) and other structurally similar proteins (i.e., lysozyme (LYZ) and chymotrypsin (CTP)). The ligand‐free Fe₃O₄/CMCS nanoclusters, in addition to their simple and economical two‐step preparation process, possess many merits, including uniform morphology, high negative charges (?27 mV), high saturation magnetization (60 emu g^?1), and high magnetic content (85%). Additionally, the ligand‐free Fe₃O₄/CMCS nanoclusters are found to selectively capture BHB in a model protein mixture even within biological samples. The reason for selective protein capture is further investigated from nanomaterials and protein structure. In terms of nanomaterials, it is found that high negative charges are conducive to selectively adsorb BHB. In consideration of protein structure, interestingly, the ligand‐free magnetic nanoclusters display a structure‐selective protein adsorption capacity to efficiently capture other proteins structurally similar to BHB, such as LYZ and CTP, showing great potential of the ligand‐free strategy in biomedical field.     

Magnetically responsive,sorafenib loaded alginate microspheres for hepatocellular carcinoma treatment

This study aimed to develop sorafenib loaded magnetic microspheres for the treatment of hepatocellular carcinoma. To achieve this goal, superparamagnetic iron oxide nanoparticles (SPIONs) were synthesised and encapsulated in alginate microspheres together with an antineoplastic agent, sorafenib. In the study, firstly SPIONs were synthesised and characterised by dynamic light scattering, energy‐dispersive X‐ray spectroscopy, and scanning electron microscopy. Then, alginate‐SPIONs microspheres were developed, and further characterised by electron spin resonance spectrometer and vibrating sample magnetometer. Besides the magnetic properties of SPIONs, alginate microspheres with SPIONs were also found to have magnetic properties. The potential use of microspheres in hyperthermia treatment was then investigated and an increase of about 4°C in the environment was found out. Drug release studies and cytotoxicity tests were performed after sorafenib was encapsulated into the magnetic microspheres. According to release studies, sorafenib has been released from microspheres for 8 h. Cytotoxicity tests showed that alginate‐SPION‐sorafenib microspheres were highly effective against cancerous cells and promising for cancer therapy.Inspec keywords: drug delivery systems, drugs, nanofabrication, magnetic particles, iron compounds, scanning electron microscopy, hyperthermia, biomedical materials, encapsulation, nanoparticles, light scattering, nanomagnetics, cellular biophysics, toxicology, cancer, nanomedicine, superparamagnetism, nanocomposites, magnetometry, paramagnetic resonance, X‐ray chemical analysisOther keywords: sorafenib loaded alginate microspheres, hepatocellular carcinoma treatment, sorafenib loaded magnetic microspheres, superparamagnetic iron oxide nanoparticles, dynamic light scattering, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy, electron spin resonance spectrometer, vibrating sample magnetometer, hyperthermia treatment, drug release, alginate‐SPION‐sorafenib microspheres, antineoplastic agent, cytotoxicity tests, cancerous cells, time 8.0 hour, Fe₃ O₄      

Polyol Synthesis of Fe3 O 4@Tween20 Nanocomposite in Vaseline Oil

For the synthesis of Fe₃O₄@Tween20 nanocomposite, two surfactants (Tween20 and oleic acid) were used to overcome the aggregation. The nanoparticles were used to prepare a water-based Fe₃O₄@Tween20 nanocomposite using oleic acid and Tween20 as surfactants ( Fe₃O₄ colloidal superparticles were developed by introducing Tween20 as a surface modification agent to maintain the colloidal stability of the F e ₃O₄ superparamagnetic nanoparticles (SPION)). Vaseline and the synthesized iron oleate were used for the polyol synthesis of Fe₃O₄@Tween20 nanocomposite. The product has superparamagnetic property. Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA) proved the presence of both surfactants on the surface of the Fe₃O₄ nanoparticles. The product may have potential use in magnetic resonance imaging and hyperthermia.     

Novel mechanochemical process for synthesis of magnetite nanoparticles using coprecipitation method

A novel coprecipitation method using a high mechanical energy field as the synthesis reaction system of magnetite (Fe₃O₄) has been developed for preparing the superparamagnetic Fe₃O₄ nanoparticles with high crystallinity in water system. In the synthesis process, the suspension containing the precipitates of ferrous hydroxide and goethite was treated in a tumbling ball mill under a cooling condition. The mechanical energy generated by collision of ball media promoted the Fe₃O₄ formation reaction and simultaneously crystallized the formed Fe₃O₄ nanoparticles without using any conventional heating techniques by means of the mechanochemical effect. The collision energy of ball media was numerically analyzed by discrete element simulation of their motion in the ball mill. Size, crystallinity and magnetization of the Fe₃O₄ nanoparticles obtained under different ball-milling conditions were almost the same regardless of the amount of the collision energy. However, the reaction rate of Fe₃O₄ formation increased with the collision energy, which was analogous to increase of the reaction rate caused by increase of the heat energy applied to the reaction system. The reaction rate depended strongly on the number of collisions with the energy larger than a threshold value corresponding to the activation energy in this reaction system.     

Preparation,characterisation and in vitro cytotoxicity studies of chelerythrine-loaded magnetic Fe3O4@O-carboxymethylchitosan nanoparticles

In this work, a novel, active tumour-targeting system (Fe₃O₄@OCMCS-CHE) was designed by surface-modifying superparamagnetic iron oxide nanoparticles (Fe₃O₄) with O-carboxymethylchitosan (OCMCS) to improve their biocompatibility and ability to target specific tumour cells. The chelerythrine (CHE) was used as the model of anti-tumour drug in this system. The optimised formulation was characterised and confirmed by scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), in vitro drug release and so on. It was found that the synthesised nanoparticles were spherical in shape with an average size of 60 nm, the drug loading content and entrapment efficiency were 8.32 ± 0.25% (w/w) and 90.65 ± 0.46% (w/w), respectively, and the saturated magnetisation reached 27.06 emu/g. The in vitro drug-release behaviour from nanoparticles displayed a biphasic drug-release pattern with initial burst release and consequently sustained release. Also, the effect of magnetic targeted nanoparticles on the proliferation of human hepatoma cell line (HepG2) in vitro was investigated. The results from 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and Hochest assays suggested that the Fe₃O₄@OCMCS-CHE nanoparticles could effectively inhibit the proliferation of HepG2 cells, which displayed time-dependent and concentration-dependent manner. All these results indicated that the multifunctional Fe₃O₄@OCMCS nanoparticles possess a high drug loading efficiency, have low cytotoxicity, and are promising candidates for targeted drug delivery.     

Enhanced Magnetism in Highly Ordered Magnetite Nanoparticle‐Filled Nanohole Arrays

A new approach to develop highly ordered magnetite (Fe₃O₄) nanoparticle‐patterned nanohole arrays with desirable magnetic properties for a variety of technological applications is presented. In this work, the sub‐100 nm nanohole arrays are successfully fabricated from a pre‐ceramic polymer mold using spin‐on nanoprinting (SNAP). These nanoholes a then filled with monodispersed, spherical Fe₃O₄ nanoparticles of about 10 nm diameter using a novel magnetic drag and drop procedure. The nanohole arrays filled with magnetic nanoparticles a imaged using magnetic force microscopy (MFM). Magnetometry and MFM measurements reveal room temperature ferromagnetism in the Fe₃O₄‐filled nanohole arrays, while the as‐synthesized Fe₃O₄ nanoparticles exhibit superparamagnetic behavior. As revealed by MFM measurements, the enhanced magnetism in the Fe₃O₄‐filled nanohole arrays originates mainly from the enhanced magnetic dipole interactions of Fe₃O₄ nanoparticles within the nanoholes and between adjacent nanoholes. Nanoparticle filled nanohole arrays can be highly beneficial in magnetic data storage and other applications such as microwave devices and biosensor arrays that require tunable and anisotropic magnetic properties.     

Enhancement of the optical and mechanical properties of chitosan using Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

In this work, the optical and mechanical properties of Fe₂O₃ nanoparticles (NPs)/chitosan nanocomposite films have been investigated. Nanocomposite films of different weight ratios of Fe₂O₃ NPs/chitosan (0, 1, 5, 10, 20 and 30 wt%) were fabricated using casting technique. The optical properties of colloidal Fe₂O₃ NPs and Fe₂O₃ NPs/chitosan nanocomposite films were recorded using UV–visible spectrophotometer. As the ratio of Fe₂O₃ NPs to chitosan increases from 0 to 30%, the energy band gap of Fe₂O₃ NPs/chitosan films decreases from 3.16 to 2.11 eV. This decrease is due to quantum confinement effect. The mechanical properties of the nanocomposite films as a function of sweeping temperature were measured using a dynamic mechanical analyzer. An enhancement in storage modulus, stiffness and glass transition temperature (T_g) has been observed as the ratio of Fe₂O₃ NPs/chitosan increases. T_g of Fe₂O₃ NPs/chitosan nanocomposite film shifts towards higher temperature side with respect to pure chitosan film from 152.1 to 166.3?°C as the ratio of Fe₂O₃ NPs/chitosan increases from 0 to 30 wt%. The increase in T_g is mainly attributed to the decrease in free volumes and vacancies in the nanocomposite films as the weight ratio of Fe₂O₃ NPs/chitosan increases.     

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.     

Magnetic nanoparticles coated with anacardic acid derived from cashew nut shell liquid

Magnetic nanoparticles functionalized with biomolecules have received special attention due to their various biomedical applications, such as drug delivery and magnetic hyperthermia treatment for cancer. In this study, we present the synthesis and characterization of new nanoparticles coated with anacardic acid derived from cashew nut shell liquid. The results showed that Fe₃O₄ nanoparticles coated with anacardic acid (AA-MAG) have superparamagnetic behavior and the magnetization is almost equal when compared with the pure Fe₃O₄. This coating provides stability by preventing the aggregation nanoparticles without losing its magnetization potential. The AA-MAG demonstrates excellent and fast magneto-temperature response which can be used as high-performance hyperthermia agents.     

Mechanochemical preparation of magnetite nanoparticles by coprecipitation

A novel simple process for preparing magnetite (Fe₃O₄) nanoparticles by a coprecipitation route without using any additives (e.g., surfactant and oxidizing and reducing agents) has been developed. In this method, a cooled ball mill was used as a synthesis reaction field in order to inhibit progress of both the synthesis reaction and the particle growth by heat energy. The Fe₃O₄ nanoparticles were formed by ball-milling of the starting suspension consisting of ferrous hydroxide and goethite colloids, and the crystallization was simultaneously progressed without heating. The obtained nanoparticles were then characterized through the SEM observation, XRD analysis, EDS analysis and oxidation-reduction titration, and the magnetic properties were measured with a SQUID magnetometer. This preparation process can provide successfully the superparamagnetic Fe₃O₄ nanoparticles of about 10 nm with high crystallinity and saturation magnetization by mechanochemical effect.     

Facile fabrication of superparamagnetic coaxial gold/halloysite nanotubes/Fe3O4 nanocomposites with excellent catalytic property for 4-nitrophenol reduction

A novel superparamagnetic gold/halloysite nanotubes/Fe₃O₄ (Au/HNTs/Fe₃O₄) nanocomposite with coaxial structure was designed and fabricated by selective decoration of the inner lumen and the external wall of halloysite nanotubes (HNTs) based on the difference inside/outside surface charges. The structure and composition of Au/HNTs/Fe₃O₄ were characterized by transmission electron microscope, powder X-ray diffraction, and X-ray fluorescence. The results indicated that Au nanorods selectively generated within the lumen of HNTs, while Fe₃O₄ nanoparticles uniformly deposited on the external wall. It was particularly worth mentioning that the structure of HNTs was not destroyed in the preparation process of Au/HNTs/Fe₃O₄ nanocomposites. The catalytic activity of the as-prepared Au/HNTs/Fe₃O₄ was investigated for the reduction of 4-nitrophenol in the presence of NaBH₄. The Au/HNTs/Fe₃O₄ nanocomposites exhibited excellent catalytic activity and cycling stability according to the kinetic data of the catalytic reduction reaction. In addition, the Au/HNTs/Fe₃O₄ catalysts can be easily manipulated by an external magnetic field for recycling.