Synthesis of monodisperse biotinylated p(NIPAAm)-coated iron oxide magnetic nanoparticles and their bioconjugation to streptavidin

We describe here the synthesis of 10 nm, monodisperse, iron oxide nanoparticles that we have coated with temperature-sensitive, biotinylated p(NIPAAm) (b-PNIPAAm). The PNIPAAm was prepared by the reversible addition fragmentation chain transfer polymerization (RAFT), and one end was biotinylated with a PEO maleimide-activated biotin to form a stable thioether linkage. The original synthesized iron oxide particles were stabilized with oleic acid. They were dispersed in dioxane, and the oleic acid molecules were then reversibly exchanged with a mixture of PNIPAAm and b-PNIPAAm at 60 degrees C. The b-PNIPAAm-coated magnetic nanoparticles were found to have an average diameter of approximately 15 nm by dynamic light scattering and transmission electron microscopy. The ability of the biotin terminal groups on the b-PNIPAAm-coated nanoparticles to interact with streptavidin was confirmed by fluorescence and surface plasmon resonance. It was found that the b-PNIPAAm-coated iron oxide nanoparticles can still bind with high affinity to streptavidin in solution or when the streptavidin is immobilized on a surface. We have also demonstrated that the binding of the biotin ligands on the surface of the temperature-responsive magnetic nanoparticles to streptavidin can be turned on and off as a function of temperature.     

基于磁性辅助的杂交链反应放大检测三磷酸腺苷

本文提出了一种基于磁性辅助的杂交链反应放大检测三磷酸腺苷(ATP)的传感策略。磁性纳米粒子表面易于修饰,而且操作方便,具有很好的分离效果,能够提高生物传感的选择性。首先,利用生物素与链霉亲和素之间的亲和力作用,将生物素标记的ATP核酸适配体连接到链霉亲和素修饰的磁性纳米粒子表面,加入与ATP核酸适配体互补的一段DNA进行杂交,通过磁性分离除去未杂交上的DNA,加入靶向ATP,ATP与其适配体特异性结合将适配体的互补链通过磁性分离出来,磁性分离出的信号DNA继续用于下一步的杂交链反应,将信号放大,最后利用氧化石墨烯(GO)对荧光的猝灭效应降低背景荧光,达到高灵敏度、高选择性检测靶向ATP。其中,ATP的最低检测浓度为0.1nmol/L。     

Fluorescence-modified superparamagnetic nanoparticles: intracellular uptake and use in cellular imaging

This report describes the preparation and characterization of new magnetic fluorescent nanoparticles and our success in using them to label living cells. The bifunctional nanoparticles possess a magnetic oxide core composed of a dimercaptosuccinic acid (DMSA) ligand at the surface and a covalently attached fluorescent dye. The nanoparticles exhibited a high affinity for cells, which was demonstrated by fluorescence microscopy and magnetophoresis. Fluorescence microscopy was used to monitor the localization patterns of magnetic nanoparticles associated with cells. We observed two types of magnetic labeling: adsorption of the nanoparticles on the cell membrane (membranous fluorescence) and internalization of the nanoparticles inside the cell (intracellular vesicular fluorescence). After internalization, nanoparticles were confined inside endosomes, which are submicrometric vesicles of the endocytotic pathway. We demonstrated that endosome movement could be piloted inside the cell by external magnetic fields such that small fluorescent chains of magnetic endosomes were formed in the cell cytoplasm in the direction of the applied magnetic field. Finally, by measuring the critical cellular magnetic load (quantitated by magnetophoresis), we have demonstrated the potential of this new magneto-fluorescent nanoagent for medical use.     

Manganese doping of magnetic iron oxide nanoparticles: tailoring surface reactivity for a regenerable heavy metal sorbent

A method for tuning the analyte affinity of magnetic, inorganic nanostructured sorbents for heavy metal contaminants is described. The manganese-doped iron oxide nanoparticle sorbents have a remarkably high affinity compared to the precursor material. Sorbent affinity can be tuned toward an analyte of interest simply by adjustment of the dopant quantity. The results show that following the Mn doping process there is a large increase in affinity and capacity for heavy metals (i.e., Co, Ni, Zn, As, Ag, Cd, Hg, and Tl). Capacity measurements were carried out for the removal of cadmium from river water and showed significantly higher loading than the relevant commercial sorbents tested for comparison. The reduction in Cd concentration from 100 ppb spiked river water to 1 ppb (less than the EPA drinking water limit of 5 ppb for Cd) was achieved following treatment with the Mn-doped iron oxide nanoparticles. The Mn-doped iron oxide nanoparticles were able to load ~1 ppm of Cd followed by complete stripping and recovery of the Cd with a mild acid wash. The Cd loading and stripping is shown to be consistent through multiple cycles with no loss of sorbent performance.     

Aptamer functionalized magnetic graphene oxide nanocomposites for highly selective capture of histones

The binding coverage of aptamer was an important restricted factor for aptamer‐based affinity enrichment strategy for capturing target molecules. Herein, we designed and prepared aptamer functionalized graphene oxide based nanocomposites (GO/NH₂‐NTA/Fe₃O₄/PEI/Au), and the coverage density of aptamer was high to 33.1 nmol/mg. The high aptamer coverage density was contributed to the large surface area of graphene oxide. The successive modification of Nα,Nα‐Bis(carboxymethyl)‐L‐lysine, magnetic nanoparticles, polyethylenimine, and Au nanoparticles ensured the histone purification with fast speed and high purity. Histones could be captured rapidly and specifically from nucleoproteins by our aptamer based purification strategy, while traditional acid‐extraction could not specifically enrich histones. Compared with traditional acid‐extraction method, rapid and efficient discovery of histones and their post‐translational modifications, such as several kinds of methylation at H3.1K9 and H3.1K27, were achieved confidently. It demonstrated that our aptamer functionalized magnetic graphene oxide nanocomposites have a great potential for histone analysis.     

Templated nucleation of hybrid iron oxide nanoparticles on polysaccharide nanogels

Novel organic–inorganic hybrid nanoparticles consisting of polymer–hydrogel nanoparticles (nanogels) and iron oxide were developed for potential biomedical applications. Hybrid nanoparticles were prepared by a simple procedure using polysaccharide nanogels as a reactive site for iron oxide formation. The hybrid nanoparticles have a narrow size distribution with a diameter of approximately 30 nm and show high colloidal stability. These nanohybrid particles could be used as a contrast medium for magnetic resonance imaging or for magnetic hyperthermia therapy.     

Preparation of a multi‐hollow magnetic molecularly imprinted polymer for the selective enrichment of indolebutyric acid

A simple strategy was developed for the preparation of multi‐hollow magnetic molecularly imprinted polymers by incorporating 3‐indolebutyric acid and ferroferric oxide nanoparticles simultaneously into a poly(styrene‐co‐methacrylic acid) copolymer matrix. The as prepared absorbents were characterized using scanning electron microscopy, Fourier‐transform infrared spectroscopy and mercury porosimetry. The adsorption isotherms of indolebutyric acid revealed that there are two types of affinity binding sites in the absorbents. The apparent maximum binding capacity and dissociation constant were 17.88 mg/g and 158.7 μg/mL for high‐affinity binding sites and 9.310 mg/g and 35.04 μg/mL for low‐affinity binding sites, respectively. The results testified that multi‐hollow magnetic molecularly imprinted polymers possessed excellent recognition capacity and fast kinetic binding behavior to the objective molecules due to the high specific surface area as large as 511.3 m²/g. Recoveries of 75.5–86.8% were obtained for the indolebutyric acid spiked at three concentration levels in blank and pear samples.     

Fabrication of magnetic core@shell Fe oxide@Au nanoparticles for interfacial bioactivity and bio-separation

The immobilization of proteins on gold-coated magnetic nanoparticles and the subsequent recognition of the targeted proteins provide an effective means for the separation of proteins via application of a magnetic filed. A key challenge is the ability to fabricate such nanoparticles with the desired core-shell nanostructure. In this article, we report findings of the fabrication and characterization of gold-coated iron oxide (Fe2O3 and Fe3O4) core@shell nanoparticles (Fe oxide@Au) toward novel functional biomaterials. A hetero-interparticle coalescence strategy has been demonstrated for fabricating Fe oxide@Au nanoparticles that exhibit controllable sizes ranging from 5 to 100 nm and high monodispersity. Composition and surface analyses have proven that the resulting nanoparticles consist of the Fe2O3 core and the Au shell. The magnetically active Fe oxide core and thiolate-active Au shell were shown to be viable for exploiting the Au surface protein-binding reactivity for bioassay and the Fe oxide core magnetism for magnetic bioseparation. These findings are entirely new and could form the basis for fabricating magnetic nanoparticles as biomaterials with tunable size, magnetism, and surface binding properties.     

Dopamine as a robust anchor to immobilize functional molecules on the iron oxide shell of magnetic nanoparticles

We report on the use of dopamine (DA) as a robust molecular anchor to link functional molecules to the iron oxide shell of magnetic nanoparticles. Using nitrilotriacetic acid (NTA) as the functional molecule, we created a system with an M/Fe2O3-DA-NTA (M = Co or SmCo5.2) nanostructure, which possesses high stability and specificity for separating histidine-tagged proteins. The well-established biocompatibility of iron oxide and the robust covalent bonds between DA and Fe2O3 render this strategy attractive for constructing biofunctional magnetic nanoparticles containing iron oxide.     

Encapsulation of magnetic and fluorescent nanoparticles in emulsion droplets

Oils containing both fluorescent semiconductor and magnetic oxide nanoparticles are used to produce oil in water emulsions. This technique produces oil droplets with homogeneous fluorescence and high magnetic nanoparticle concentrations. The optical properties of the oil droplets are studied as a function of the droplet sizes for various concentrations of fluorescent and magnetic nanoparticles. For all concentrations tested, we find a linear variation of the droplet fluorescent intensity as a function of the droplet volume. For a given size and a given quantum dot (QD) concentration, the droplet fluorescence intensity drops sharply as a function of the magnetic nanoparticle concentration. We show that this decrease is due mainly to the strong absorption cross section of the magnetic nanoparticles and to a lesser extent to the dynamic and static quenching of the QD fluorescence. The role of the iron oxide nanoparticle localization in the droplet (surface versus volume) is also discussed.     

Preparation of Cerium Dioxide Functionalized Magnetic Layered Double Hydroxides for High-efficiency Phosphopeptide Enrichment

In this work, we prepared a material with magnetic nanoparticles (Fe₃O₄) as core, layered double hydroxides(LDHs) as affinity shell, and cerium dioxide(CeO₂) as functional molecules(denoted as Fe₃O₄@LDH-CeO₂). On the basis of combined immobilized metal ion affinity chromatography(IMAC) and metal oxide affinity chromatography(MOAC), Fe₃O₄@LDH-CeO₂ was used to enrich phosphopeptides with high efficiency. The material exhibited high selectivity(α-casein:β-casein:BSA=1:1:5000, mass ratio), high recovery(95.87%), and good reusability of 10 times adsorption- desorption experiments. The feasibility of Fe₃O₄@LDH-CeO₂ was further investigated by extracting phosphopeptides from biological samples(nonfat milk, serum, saliva, and A549 cell lysate).     

A Comparative Study of Receptor-Targeted Magnetosome and HSA-Coated Iron Oxide Nanoparticles as MRI Contrast-Enhancing Agent in Animal Cancer Model

Magnetosomes are specialized organelles arranged in intracellular chains in magnetotactic bacteria. The superparamagnetic property of these magnetite crystals provides potential applications as contrast-enhancing agents for magnetic resonance imaging. In this study, we compared two different nanoparticles that are bacterial magnetosome and HSA-coated iron oxide nanoparticles for targeting breast cancer. Both magnetosomes and HSA-coated iron oxide nanoparticles were chemically conjugated to fluorescent-labeled anti-EGFR antibodies. Antibody-conjugated nanoparticles were able to bind the MDA-MB-231 cell line, as assessed by flow cytometry. To compare the cytotoxic effect of nanoparticles, MTT assay was used, and according to the results, HSA-coated iron oxide nanoparticles were less cytotoxic to breast cancer cells than magnetosomes. Magnetosomes were bound with higher rate to breast cancer cells than HSA-coated iron oxide nanoparticles. While 250 μg/ml of magnetosomes was bound 92 ± 0.2%, 250 μg/ml of HSA-coated iron oxide nanoparticles was bound with a rate of 65 ± 5%. In vivo efficiencies of these nanoparticles on breast cancer generated in nude mice were assessed by MRI imaging. Anti-EGFR-modified nanoparticles provide higher resolution images than unmodified nanoparticles. Also, magnetosome with anti-EGFR produced darker image of the tumor tissue in T2-weighted MRI than HSA-coated iron oxide nanoparticles with anti-EGFR. In vivo MR imaging in a mouse breast cancer model shows effective intratumoral distribution of both nanoparticles in the tumor tissue. However, magnetosome demonstrated higher distribution than HSA-coated iron oxide nanoparticles according to fluorescence microscopy evaluation. According to the results of in vitro and in vivo study results, magnetosomes are promising for targeting and therapy applications of the breast cancer cells.     

Magnetic hyperthermia: Potentials and limitations

Despite the fact that the magnetic hyperthermia (MH) has been known for more than 75 years, it is still debated in its clinical applications. The generation of a higher temperature at a tumor is called hyperthermia. There is a different of temperature ranges going from 39 to 40 ?°C up to such high temperatures as 80–90 ?°C. However, due to its high potential, MH is used along with nanoparticles as heat intermediaries in the treatment of cancer. Many Magnetic Nanoparticles (MNPs) with several properties and morphological metallic structures have been useful to magnetics hyperthermia therapy. These MNPs are categorized into two groups; magnetic alloy nanoparticles (MANPs) and magnetic metal oxide nanoparticles (MMONPs). The principal challenges of this method are the control of local tumoral temperature and the increase in nanoparticles heating power. The hyperthermia agents derived from magnetic nanoparticles along with magnetic field. In the recent study, hyperthermia thought, dissimilar types of magnetic nanoparticles for hyperthermia, efficacy for cancer therapy, advances, challenges, and future chances have been examined.     

An NMR-relaxation study of the effect of albumin on aggregation of magnetic iron oxide nanoparticles

The dependence of the aggregation of magnetic iron oxide nanoparticles in aqueous suspensions under the action of human serum albumin is analyzed based on the data of proton magnetic relaxation. It is shown that albumin adsorption on magnetic nanoparticles gives rise to the formation of a protein corona and clusters of magnetic nanoparticles, decreasing the aggregation stability of the suspension in a 7.1-T magnetic field. Clustering of magnetic iron oxide nanoparticles enhances the relaxation efficiency of magnetic suspensions during NMR measurements.     

A Bioorthogonal Small‐Molecule‐Switch System for Controlling Protein Function in Live Cells

Chemically induced dimerization (CID) has proven to be a powerful tool for modulating protein interactions. However, the traditional dimerizer rapamycin has limitations in certain in vivo applications because of its slow reversibility and its affinity for endogenous proteins. Described herein is a bioorthogonal system for rapidly reversible CID. A novel dimerizer with synthetic ligand of FKBP′ (SLF′) linked to trimethoprim (TMP). The SLF′ moiety binds to the F36V mutant of FK506‐binding protein (FKBP) and the TMP moiety binds to E. coli dihydrofolate reductase (eDHFR). SLF′‐TMP‐induced heterodimerization of FKBP(F36V) and eDHFR with a dissociation constant of 0.12 μM . Addition of TMP alone was sufficient to rapidly disrupt this heterodimerization. Two examples are presented to demonstrate that this system is an invaluable tool, which can be widely used to rapidly and reversibly control protein function in vivo.     

Surface functionalization and characterization of magnetic polystyrene microbeads

A new approach to the surface functionalization of magnetic polystyrene microbeads with chloroacetyl chloride in the presence of aluminum chloride was reported. Composite microbeads consisting of polymer-coated iron oxide nanoparticles were prepared by spraying suspension polymerization. Functional chloride groups were introduced onto the surface of magnetic polystyrene microbeads by surface chemical reaction without destroying the magnetite nanoparticles within the microbeads. First, a complex was synthesized by a reaction between aluminum chloride and chloroacetyl chloride. Then, the complex was added dropwise to the solution of magnetic polystyrene microbeads, and a surface acylation reaction between complex and polystyrene microbeads was carried out. Subsequently, the amino groups were coupled to the magnetic microbeads via an ammonolysis reaction between ethylenediamine and chloride groups on the acylated magnetic polystyrene microbeads. The chemical composition, surface functional groups, and magnetism of the magnetic polystyrene microbeads before and after surface functionalization were characterized by Fourier transform infrared spectroscopy and vibrating sample magnetometry. The results showed that the surface functionalization reaction had little impact on the magnetism of the microbeads. The content of surface amino groups on the magnetic polystyrene microbeads was found to be 0.2 mmol/g. An affinity dye, Cibacron Blue F3G-A (CB), was then immobilized to prepare a magnetic affinity adsorbent. It was confirmed from X-ray photoelectron spectroscopy spectra that the CB molecules were covalently coupled on the magnetic microbeads.     

Iron Oxide Nanoparticles Embedded onto 3D Mesochannels of KIT‐6 with Different Pore Diameters and Their Excellent Magnetic Properties

Here, we report the results of our detailed study on the fabrication of iron oxide magnetic nanoparticles confined in mesoporous silica KIT‐6 with a 3D structure and large, tunable pore diameters. It was confirmed by XRD, nitrogen adsorption, high‐resolution (HR) TEM, and magnetic measurements that highly dispersed iron oxide nanoparticles are occupied inside the mesochannels of KIT‐6. We also demonstrated that the size of the iron oxide nanoparticle can be controlled by simply changing the pore diameter of the KIT‐6 and the weight percentage of the iron oxide nanoparticles. The effect of the weight percentage and size of the iron oxide nanoparticles, and the textural parameters of the support on the magnetic properties of iron oxide/KIT‐6 has been demonstrated. The magnetization increases with decreasing iron content in the pore channels of KIT‐6, whereas coercivity decreases for the same samples. Among the KIT‐6 materials studied, KIT‐6 with 7.5 wt % of iron showed the highest saturation magnetic moment and magnetic remanence. However, all the samples register a coercivity of around 2000 Oe, which is generally observed for the hard magnetic materials. In addition, we have found a paramagnetic‐to‐superparamagnetic transition at low temperature for samples with different iron content at low temperature. The cause for this exciting transition is also discussed in detail. Magnetic properties of the iron oxide loaded KIT‐6 were also compared with pure iron oxide and iron oxide loaded over SBA‐15. It was found that iron oxide loaded KIT‐6 showed the highest magnetization due to its 3D structure and large pore volume. The pore diameter of the iron oxide loaded KIT‐6 support also plays a critical role in controlling the magnetization and the blocking temperature, which has a direct relation to the particle diameter and increases from 48 to 63 K with an increase in the pore diameter of the support from 8 to 11.3 nm.     

Tris(hydroxymethyl)aminomethane-modified magnetic microspheres for rapid affinity purification of lysozyme

A novel affinity purification method for lysozyme (LZM) based on functionalized magnetic microspheres was developed. Tris(hydroxymethyl)aminomethane (Tris)-modified magnetic microspheres with specific affinity toward LZM were prepared using Tris as ligand and silica-coated magnetic microshperes as support. Transmission electron microscopy and magnetic property measurement results showed that the Tris-modified magnetic microspheres have a very good core-shell structure and high magnetization.The maximum binding capacity of LZM was about 108.6 mg/g magnetic microspheres. LZM purified from chicken egg white had high purity and well-maintained activity of 8140 U/mg. This magnetic-mediated LZM purification strategy has advantages of high efficiency, low cost and easy operation.     

Synthesis of aligned hematite nanoparticles on chitosan–alginate films

Iron oxide nanoparticles are being viewed with interest owing to the great potential they have in the biomedical applications like MRI contrast enhancement, targeted drug delivery, hyperthermia and recently in magnetic separation of cancer cells from the body. Templated synthesis has been considered ideal for synthesis of iron oxide nanoparticles as particles are attracted magnetically, in addition to usual flocculation through van der Waals attraction. Biological templates are attractive owing to their biocompatibility and the attractive porosity and surface chemistry that nature provides. Polysaccharides like chitosan and alginate have been employed in the synthesis of a polyion complex, which provided the active-binding sites for iron(II) ions in solution to bind. The natural organization of chitosan and alginate into a porous film has been exploited to synthesize spherical iron oxide nanoparticles through careful calcination of the iron(II) conjugate film. Our experiments indicate that the formed nanoparticles are highly crystalline, confirm to the hematite structure and have a superparamagnetic response with a low coercivity of 116 Oe. Particles thus synthesized were highly monodisperse with hydrodynamic diameter of 1.8 nm. The symmetric porosity of the film translates into the synthesis of well-aligned nanoparticles of iron oxide. Compared to synthesis in solution, the film-assisted synthesis offered a greater degree of control over the particle size distribution pattern, with the chitosan–alginate template providing the needed spatial separation to prevent the aggregation due to magnetostatic coupling. Such hematite nanoparticles can either be used directly or converted to paramagnetic magnetite by reduction. Zeta potential measurements indicate highly stable nanoparticles, which can therefore be conjugated to cationic liposomes carrying drugs and magnetically guided to target sites.     

Protein Denaturation Through the Use of Magnetic Molecularly Imprinted Polymer Nanoparticles

The inhibition of the protein function for therapeutic applications remains challenging despite progress these past years. While the targeting application of molecularly imprinted polymer are in their infancy, no use was ever made of their magnetic hyperthermia properties to damage proteins when they are coupled to magnetic nanoparticles. Therefore, we have developed a facile and effective method to synthesize magnetic molecularly imprinted polymer nanoparticles using the green fluorescent protein (GFP) as the template, a bulk imprinting of proteins combined with a grafting approach onto maghemite nanoparticles. The hybrid material exhibits very high adsorption capacities and very strong affinity constants towards GFP. We show that the heat generated locally upon alternative magnetic field is responsible of the decrease of fluorescence intensity.