Gold nanoparticle/polymer nanocomposites: dispersion of nanoparticles as a function of capping agent molecular weight and grafting density

The dispersion of polymer-covered gold nanoparticles in high molecular weight (MW) polymer matrixes is reported. Complete particle dispersion was achieved for PS125-Au in the polystyrene (PS) matrixes studied (up to and including Mn = 80 000 g/mol). PS19-Au, on the other hand, exhibits complete dispersion in a low MW PS matrix (Mn = 2000 g/mol) but only partial dispersion in higher MW matrixes (up to 80 000 g/mol). Similarly, PEO45-Au is fully dispersed in a low MW poly(ethylene oxide) (PEO) matrix (Mn = 1000 g/mol) but only partially in a higher MW PEO matrix (Mn = 15 000 g/mol). Wetting of the polymer-Au brushes by the polymer matrix is associated with dispersibility. Theory predicts that, for dense polymer brushes, wetting is achieved when the MW of the polymer brush equals (and is greater than) that of the polymer matrix. The observed partial dispersion of the PS19-Au and PEO45-Au nanoparticles in matrixes whose MW is greater than the brush MW is attributable to the existence of a high volume fraction of voids within the brush. These voids arise from the unique geometry of the nanoparticle surface arising from the juxtaposed facets of the gold nanoparticle. PS125-Au brushes are wetted by PS matrixes whose degree of polymerization is larger than 125, probably because of their lower grafting density on the gold core or the high fraction of void volumes caused by the facets on the gold cores. Dispersion thus occurs when the matrix MW is greater than that of the brush.     

Magnetic force-based multiplexed immunoassay using superparamagnetic nanoparticles in microfluidic channel

This paper describes a novel microfluidic immunoassay utilizing binding of superparamagnetic nanoparticles to beads and deflection of these beads in a magnetic field as the signal for measuring the presence of analyte. The superparamagnetic 50 nm nanoparticles and fluorescent 1 microm polystyrene beads are immobilized with specific antibodies. When target analytes react with the polystyrene beads and superparamagnetic nanoparticles simultaneously, the superparamagnetic nanoparticles can be attached onto the microbeads by the antigen-antibody complex. In the poly(dimethylsiloxane)(PDMS) microfluidic channel, only the microbeads conjugated with superparamagnetic nanoparticles by analytes consequently move to the high gradient magnetic fields under the specific applied magnetic field. In this study, the magnetic force-based microfluidic immunoassay is successfully applied to detect the rabbit IgG and mouse IgG as model analytes. The lowest concentration of rabbit IgG and mouse IgG measured over the background is 244 pg mL(-1) and 15.6 ng mL(-1), respectively. The velocities of microbeads conjugated with superparamagnetic nanoparticles are demonstrated by magnetic field gradients in microfluidic channels and compared with the calculated magnetic field gradients. Moreover, dual analyte detection in a single reaction is also performed by the fluorescent encoded microbeads in the microfluidic device. Detection range and lower detection limit can be controlled by the microbeads concentration and the higher magnetic field gradient.     

A micropillar-integrated smart microfluidic device for specific capture and sorting of cells

An integrated smart microfluidic device consisting of nickel micropillars, microvalves, and microchannels was developed for specific capture and sorting of cells. A regular hexagonal array of nickel micropillars was integrated on the bottom of a microchannel by standard photolithography, which can generate strong induced magnetic field gradients under an external magnetic field to efficiently trap superparamagnetic beads (SPMBs) in a flowing stream, forming a bed with sufficient magnetic beads as a capture zone. Fluids could be manipulated by programmed controlling the integrated air-pressure-actuated microvalves, based on which in situ bio-functionalization of SPMBs trapped in the capture zone was realized by covalent attachment of specific proteins directly to their surface on the integrated microfluidic device. In this case, only small volumes of protein solutions (62.5 nL in the capture zone; 375 nL in total volume needed to fill the device from inlet A to the intersection of outlet channels F and G) can meet the need for protein! The newly designed microfluidic device reduced greatly chemical and biological reagent consumption and simplified drastically tedious manual handling. Based on the specific interaction between wheat germ agglutinin (WGA) and N-acetylglucosamine on the cell membrane, A549 cancer cells were effectively captured and sorted on the microfluidic device. Capture efficiency ranged from 62 to 74%. The integrated microfluidic device provides a reliable technique for cell sorting.     

Free-standing poly(L-lactic acid) nanofilms loaded with superparamagnetic nanoparticles

Freely suspended nanocomposite thin films based on soft polymers and functional nanostructures have been widely investigated for their potential application as active elements in microdevices. However, most studies are focused on the preparation of nanofilms composed of polyelectrolytes and charged colloidal particles. Here, a new technique for the preparation of poly(l-lactic acid) free-standing nanofilms embeddidng superparamagnetic iron oxide nanoparticles is presented. The fabrication process, based on a spin-coating deposition approach, is described, and the influence of each production parameter on the morphology and magnetic properties of the final structure is investigated. Superparamagnetic free-standing nanofilms were obtained, as evidenced by a magnetization hysteresis measurement performed with a superconducting quantum interference device (SQUID). Nanofilm surface morphology and thickness were evaluated by atomic force microscopy (AFM), and the nanoparticle dispersion inside the composites was investigated by transmission electron microscopy (TEM). These nanofilms, composed of a biodegradable polyester and remotely controllable by external magnetic fields, are promising candidates for many potential applications in the biomedical field.     

Preparation of novel bovine hemoglobin surface-imprinted polystyrene nanoparticles with magnetic susceptibility

In this research, a surface imprinting strategy has been adopted in protein imprinting. Bovine hemoglobin surface-imprinted polystyrene (PS) nanoparticles with magnetic susceptibility have been synthesized through multistage core-shell polymerization system using 3-aminophenylboronic acid (APBA) as functional and cross-linking monomers. Superparamagnetic molecularly imprinted polystyrene nanospheres with poly(APBA) thin films have been synthesized and used for the first time for protein molecular imprinting in an aqueous solution. The magnetic susceptibility is imparted through the successful encapsulation of Fe₃O₄ nanoparticles. The morphology, adsorption, and recognition properties of superparamagnetic molecularly imprinted polymers (MIPs) have been investigated using transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer. Rebinding experimental results show that poly(APBA) MIPs-coated superparamagnetic PS nanoparticles have high adsorption capacity for template protein bovine hemoglobin and comparatively low nonspecific adsorption. The imprinted superparamagnetic nanoparticles could easily reach the adsorption equilibrium and achieve magnetic separation in an external magnetic field, thus avoiding some problems of the bulk polymer.     

Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers: from micelles to vesicles

We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.     

A novel superparamagnetic surface molecularly imprinted nanoparticle adopting dummy template: An efficient solid-phase extraction adsorbent for bisphenol A

Leakage of the residual template molecules is one of the biggest challenges for application of molecularly imprinted polymer (MIP) in solid-phase extraction (SPE). In this study, bisphenol F (BPF) was adopted as a dummy template to prepare MIP of bisphenol A (BPA) with a superparamagnetic core–shell nanoparticle as the supporter, aiming to avoid residual template leakage and to increase the efficiency of SPE. Characterization and test of the obtained products (called mag-DMIP beads) revealed that these novel nanoparticles not only had excellent magnetic property but also displayed high selectivity to the target molecule BPA. As mag-DMIP beads were adopted as the adsorbents of solid-phase extraction for detecting BPA in real water samples, the recoveries of spiked samples ranged from 84.7% to 93.8% with the limit of detection of 2.50 pg mL⁻¹, revealing that mag-DMIP beads were efficient SPE adsorbents.     

Study of the colloidal stability of concentrated bimodal magnetic fluids

In this paper, we describe an investigation of the stability and sedimentation behavior of moderately concentrated suspensions of extremely bimodal magnetite particles, including micro- (diameter 1450 nm) and nano- (diameter 8 nm) units. An original method is used, based on the determination of the time dependence of the inductance of a coil surrounding the suspensions. The method proves to be very useful for the determination of the volume fraction of magnetic material in the sensed volume. The observed changes in the resonant frequency of a parallel LC circuit demonstrate that the addition of the magnetite nanoparticles improves the stability and slows down the settling rate of the mixed suspensions. It is proposed that the observed behavior is the result of competition between two processes. One is the formation of a cloud of nanoparticles around the large magnetite units, by virtue of which the latter are maintained at distances beyond the range of DLVO and magnetic attractive interactions. At long times, these composite units will eventually sediment when some critical size is reached, as the small particles are progressively associated with the large ones. The second mechanism is mainly predominant at short times and is related to the higher viscosity of the dispersion medium (the nanoparticles dispersed in the base fluid) for higher nanoparticle concentrations. The stability of the suspensions is discussed in terms of the competition between the two mechanisms.     

Preparation and characterization of thermosensitive polymers grafted onto silica-coated iron oxide nanoparticles

In this study, multifunctional nanoparticles containing thermosensitive polymers grafted onto the surfaces of 6-nm monodisperse Fe(3)O(4) magnetic nanoparticles coated by silica were synthesized using reverse microemulsions and free radical polymerization. The magnetic properties of SiO(2)/Fe(3)O(4) nanoparticles show superparamagnetic behavior. Thermosensitive PNIPAM (poly(N-isopropylacrylamide)) was then grafted onto the surfaces of SiO(2)/Fe(3)O(4) nanoparticles, generating thermosensitive and magnetic properties of nanocomposites. The sizes of fabricated nanoparticles with core-shell structure are controlled at about 30 nm and each nanoparticle contains only one monodisperse Fe(3)O(4) core. For thermosensitivity analysis, the phase transition temperatures of multifunctional nanoparticles measured using DSC was at around 34-36 degrees C. The magnetic characteristics of these multifunctional nanoparticles were also superparamagnetic.     

NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.     

Controlled placement of polystyrene-grafted CdSe nanoparticles in self-assembled block copolymers

Surface functionalization of semiconductor CdSe nanoparticles has been achieved with polystyrene (PS) brushes by “grafting from” technique for further addition to a polystyrene-b-polybutadiene-b-polystyrene (SBS) block copolymer in order to obtain self-assembled composites. For modification of nanoparticle surface 3-glycidoxypropyltrimethoxysilane (GPS) was used at first for the later attachment of the 4,4′-azobis(4-cyanopentanoic acid) azo initiator. Fourier-transform infrared spectroscopy confirmed the presence of GPS and PS on the surface of nanoparticles. Atomic force microscopy was used for morphological characterization of SBS/CdSe nanocomposites. Modification of nanoparticles with PS brushes by radical polymerization improved their affinity with PS block and the dispersion of nanoparticles avoiding agglomeration. CdSe nanoparticle size was measured to be around 2 nm by the use of X-ray diffraction and UV–Vis techniques. Optical properties were characterized using fluorescence measurements.     

Liquid-liquid phase-transfer of magnetic nanoparticles in organic solvents

We report a novel route for the preparation of well-defined colloidal dispersions of magnetic nanoparticles stabilized by steric repulsion in organic solvents. The usual methods standardly lead to the surfaction of multiparticle aggregates, incompatible with our long-term aim of studying and modeling the influence of magnetic dipolar interactions in colloidal dispersions which are free of aggregates, all other interactions being perfectly defined. A new and reproducible method based on a surfactant-mediated liquid-liquid phase transfer of individually dispersed gamma-Fe(2)O(3) nanoparticles from an aqueous colloidal dispersion to an organic phase is developed. The choice of the reagent and the preparation techniques is discussed. Among several solvent/surfactant pairs, the cyclohexane/dimethyldidodecylammonium bromide (DDAB) system is found to fulfill the colloidal stability criterion: aggregation does not appear, even upon aging. A complete transfer of isolated particles is observed above a threshold in DDAB concentration. The nanoparticle surface is then fully covered with adsorbed DDAB molecules, each surfactant head occupying a surface of 0.57+/-0.05 nm(2). The volume fraction of the cyclohexane-based organosols is easily tunable up to a volume fraction of 12% by modifying the volume ratio of the organic and of the aqueous phases during the liquid-liquid phase transfer.     

Generation of core/shell iron oxide magnetic nanoparticles with polystyrene brushes by atom transfer radical polymerization

The functionalization of nanoparticle surfaces is required to improve the dispersion of an inorganic material inside an organic matrix. In this work, polystyrene (PS) brushes were grown on the surface of iron oxide magnetic nanoparticles with atom transfer radical polymerization and a grafting‐from approach. After polymerization, the magnetic nanoparticles had a graft density of 0.9 PS chains/nm². A sacrificial initiator was used to obtain a satisfactory result for the control of the polymerization, as its addition had to generate a sufficient concentration of persistent radicals (deactivator). A variety of techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, water contact‐angle measurements, and atomic force microscopy, were used to characterize the nanoparticles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4744–4750, 2007     

The interplay of catechol ligands with nanoparticulate iron oxides

The unique properties exhibited by nanoscale materials, coupled with the multitude of chemical surface derivatisation possibilities, enable the rational design of multifunctional nanoscopic devices. Such functional devices offer exciting new opportunities in medical research and much effort is currently invested in the area of "nanomedicine", including: multimodal imaging diagnostic tools, platforms for drug delivery and vectorisation, polyvalent, multicomponent vaccines, and composite devices for "theranostics". Here we will review the surface derivatisation of nanoparticulate oxides of iron and iron@iron-oxide core-shells. They are attractive candidates for MRI-active therapeutic platforms, being potentially less toxic than lanthanide-based materials, and amenable to functionalisation with ligands. However successful grafting of groups onto the surface of iron-based nanoparticles, thus adding functionality whilst preserving their inherent properties, is one of the most difficult challenges for creating truly useful nanodevices from them. Functionalised catechol-derived ligands have enjoyed success as agents for the masking of superparamagnetic iron-oxide particles, often so as to render them biocompatible with medium to long-term colloidal stability in the complex chemical environments of biological milieux. In this perspective, the opportunities and limitations of functionalising the surfaces of iron-oxide nanoparticles, using coatings containing a catechol-derived anchor, are analysed and discussed, including recent advances using dopamine-terminated stabilising ligands. If light-driven ligand to metal charge transfer (LMCT) processes, and pH-dependent ligand desorption, leading to nanoparticle degradation under physiologically relevant conditions can be suppressed, colloidal stability of samples can be maintained and toxicity ascribed to degradation products avoided. Modulation of the redox behaviour of iron catecholate systems through the introduction of an electron-withdrawing substituent to the aromatic π-system of the catechol is a promising approach towards achieving these goals.     

多功能磁性纳米粒的合成、修饰及生物医学应用

多功能磁性纳米粒由于其独特的性质而受到广泛的关注。磁性纳米粒可以与荧光探针、生物靶向分子或抗肿瘤药物等相结合实现磁性纳米粒的多功能化,因此在多模式成像、癌症的靶向诊断与治疗中有较好的应用前景。本文介绍了磁性纳米粒的合成以及多功能磁性纳米粒的构建方法,重点介绍了核壳型、哑铃型和组合杂化型三种不同类型多功能磁性纳米粒的合成方法。多功能磁性纳米粒通常具有粒径小、超顺磁性以及荧光等独特性质,在此基础上对纳米粒表面进行稳定化和靶向性修饰后即可在多模式成像、特异性靶向药物输送、基因转染等生物医学领域得到应用。最后指出了当前研究中需要解决的问题。     

Control of nanoparticle dispersion in SPAES/SiO2 composite proton conductors and its influence on DMFC membrane performance

A novel approach for effectively dispersing SiO₂ nanoparticles in a sulfonated poly(arylene ether sulfone) ionomer (SPAES) matrix has been demonstrated. It is based on the application of wet-type milling process. Compared to a conventional mixing process such as sonication, wet-type milling allowed noticeable improvements in SiO₂ nanoparticle dispersion, owing to the intensive impact of collisions between milling beads and nanoparticles. In terms of nanoparticle dispersion, the influence of wet-type milling on the direct methanol fuel cells (DMFC) membrane performance such as proton conductivity, methanol permeability, and selectivity was examined and compared with sonication process. This study underlines that nanoparticle dispersion in the composite membranes is crucial in determining DMFC membrane performance and can be substantially improved by employing a novel mixing process, i.e. wet-type milling.     

The force acting on a superparamagnetic bead due to an applied magnetic field

This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.     

Preparation and characterization of a polystyrene/bovine serum albumin nanoparticle‐coated capillary for chiral separation using open‐tubular capillary electrochromatography

Polystyrene (PS) nanoparticles coated by BSA, hereafter denoted as PS/BSA, were prepared and chemically immobilized for the first time onto a capillary inner wall for open‐tubular CEC (OTCEC). EOF and scanning electron micrography were used to characterize the prepared nanoparticle‐coated capillaries. To investigate the performance of the prepared columns in OTCEC, chiral separation of d ,l ‐tryptophan (dl ‐Trp) was performed in monolayer BSA‐modified capillary and PS/BSA nanoparticle‐coated columns. The results indicated that the nanoparticle‐modified column afforded a higher resolution compared with the monolayer type. Rapid enantioseparation of dl ‐Trp (within 3 min) was achieved with the PS/BSA‐immobilized column using an electroosmotic pump‐assisted CEC. Enantiomer separations of other compounds like dl ‐tyrosine and warfarin were also achieved with the column. Besides, run‐to‐run and column‐to‐column repeatabilities of the PS/BSA‐coated column in the chiral separation were systematically introduced.     

Glucose oxidase–magnetite nanoparticle bioconjugate for glucose sensing

Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of magnetite (Fe₃O₄) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase to the amino-modified nanoparticle surface. Functionalization of the magnetic nanoparticle surface with amino groups greatly increased the amount and activity of the immobilized enzyme compared with immobilization procedures involving physical adsorption. The enzymatic activity of the glucose oxidase-coated magnetic nanoparticles was investigated by monitoring oxygen consumption during the enzymatic oxidation of glucose using a ruthenium phenanthroline fluorescent complex for oxygen sensing. The glucose oxidase-coated magnetite nanoparticles could function as nanometric glucose sensors in glucose solutions of concentrations up to 20 mmol L^–1. Immobilization of glucose oxidase on the nanoparticles also increased the stability of the enzyme. When stored at 4°C the nanoparticle suspensions maintained their bioactivity for up to 3 months.     

Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles

4-Dimethylaminopyridine (DMAP)-stabilized palladium nanoparticles with a mean diameter of 3.4 +/- 0.5 nm are prepared from the aqueous phase reduction of Na2PdCl4 using NaBH4 in the presence of DMAP. TEM and UV-vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation. 1H NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP)4(OH)2 by X-ray crystallography. Following extensive analysis, it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms alpha to the endocyclic nitrogen atom on the DMAP-stabilizing ligands through reaction with D2O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.