Photo-induced magnetic bistability in a controlled assembly of anisotropic coordination nanoparticles

Anisotropic coordination nanoparticles of the photomagnetic network Cs(I)(2)Cu(II)(7)[Mo(IV)(CN)(8)](4) are obtained through a surfactant-free high-yield synthetic procedure in water. These particles are organised as Langmuir-Blodgett films with a preferential orientation of the nano-objects within the film that exhibit a magnetic bistability below 20 K with a very large coercivity due to an efficient photo-transformation.     

Heterodimeric particle assemblies: preparation of anisotropically connected spherical silica particles via surface-bound gold nanoparticles

Assemblies of heterodimeric particles were prepared through selective coupling of two kinds of spherical silica particles of different sizes by connection with gold nanoparticles attached anisotropically to the particles.     

pH-Triggered controlled drug release from mesoporous silica nanoparticles via intracelluar dissolution of ZnO nanolids

Acid-decomposable, luminescent ZnO quantum dots (QDs) have been employed to seal the nanopores of mesoporous silica nanoparticles (MSNs) in order to inhibit premature drug (doxorubicin) release. After internalization into HeLa cells, the ZnO QD lids are rapidly dissolved in the acidic intracellular compartments, and as a result, the loaded drug is released into the cytosol from the MSNs. The ZnO QDs behave as a dual-purpose entity that not only acts as a lid but also has a synergistic antitumor effect on cancer cells. We anticipate that these nanoparticles may prove to be a significant step toward the development of a pH-sensitive drug delivery system that minimizes drug toxicity.     

Preparation of raspberry-like silica microcapsules via sulfonated polystyrene template and aniline medium assembly method

Raspberry-like composite particles and microcapsules were prepared with anionic sulfonated polystyrene (PSS) particles as templates and cationic aniline monomer as assembly medium. With the help of the sulfonated microgel shells, aniline and silica particles could not only adsorbed onto template surfaces but also go inward shells and finally form microcapsules with varied silica shell thickness. The sulfonation extent of PSS particles first climbed up and then decreased with sulfonation time due to the competition of sulfonation reaction and PSS chain detachment. The silica content in composite particles and shell thickness of microcapsules followed similar trend with sulfonation extent. The choice of aniline as assembly medium was checked by comparing with methyl methacrylate and [2-(methacryloyloxy) ethyl] trimethylammonium chloride, and it was found that the cationic and water-insoluble properties of aniline are both important for the composite efficiency.     

Electrostatic assembly of core-corona silica nanoparticles onto cotton fibers

In this investigation core-corona silica nanoparticles were employed to decorate cotton fibers using electrostatic forces. The resultant composites of silica and cellulose were characterized by FESEM and TEM techniques revealed that layers of the core-corona silica deposited on cotton fibers were more uniform and smoother than those of colloidal silica nanoparticles. This improvement was mostly due to the enhanced dispersion and stabilization capabilities of the covalently bonded corona of silica nanoparticles. Experimental results also unveiled that the adsorption amount of nano core-corona silica materials was strongly governed by the surface charge density and charge strength of the cellulosic substrates. The incorporation of core-corona nanoparticles on cotton will provide a wide range of applications for this natural substrate as the surface properties can be fine tuned by a judicious choice of core, corona materials or by attaching complementary organic or inorganic shells (nano particles or polymers) to the charged corona.     

Reversible controlled assembly of thermosensitive polymer-coated gold nanoparticles

Aggregation of thermosensitive polymer-coated gold nanoparticles was performed in aqueous solution in the presence of a triblock copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic P123, PEO(20)-PPO(68)-PEO(20)). The gold nanoparticles, AuNPs, which are covered by thermosensitive statistical copolymers poly(EO(x)-st-PO(y)), aggregate when the temperature is higher than the phase transition temperature of the polymer, leading to a macroscopic precipitation. The presence of Pluronic chains in solution prevents the uncontrolled aggregation of the AuNPs at higher temperature than both the aggregation temperature of the AuNPs (T(agg)) and the critical micellization temperature (cmt) of the Pluronic. The size, the colloidal stability, and the optical properties of the AuNPs aggregates are modulated as a function of the P123-to-AuNP ratio, which constitutes the critical parameter of the system. Moreover, the AuNP aggregation is totally reversible upon decreasing the temperature below T(agg). Our approach constitutes an easy way to the formation of well-controlled nanoparticle aggregates with well-defined sizes. The resulting aggregates have been characterized by UV-vis spectroscopy, dynamic light scattering, and electron microscopy.     

Novel spherical assembly of gold nanoparticles mediated by a tetradentate thioether

The ability to construct three- and two-dimensional architectures via nanoscale engineering is important for emerging applications of nanotechnology in sensors, catalysis, controlled drug delivery, microelectronics, and medical diagnostics. In this paper, we report novel 3D assembly using multidentate molecular building blocks. It is demonstrated that the interparticle linking of gold nanoparticles (3.7 nm core size) by a tetradentate thioether, tetra[(methylthio)methyl]silane, leads to the formation of a spherical assembly. The spherical size (30-80 nm diameter) is dependent on reaction time and relative ratio of the building blocks. The novelty of this approach is the viability of multidentate thioethers to link nanoparticles and produce spherical assemblies that can be readily assembled and disassembled. The spherical assembly can also be partially "melted" depending on the nature of interfacial interactions between the assembly and the substrate. These unusual morphological properties in shape and surface interaction and the intriguing assembling-disassembling capabilities may form the basis of designing and fabricating novel functional nanostructures.     

Synthesis of zwitterionic polymer brushes hybrid silica nanoparticles via controlled polymerization for highly efficient enrichment of glycopeptides

Zwitterionic hydrophilic interaction chromatography (ZIC-HILIC) materials have been increasingly attractive in glycopeptide enrichment. However, the traditional ZIC-HILIC materials are modified with monolayer zwitterionic molecules on the surface, therefore, the hydrophilicity, detection sensitivity and loading capacity are limited. In this work, we synthesized novel silica nanoparticles with uniform poly(2-(methacryloyloxy)ethyl)dimethyl-(3-sul-fopropyl)ammonium hydroxide (PMSA) brushes grafted onto the surface via reversible addition-fragmentation chain transfer (RAFT) polymerization (denoted as SiO₂-RAFT@PMSA). The resulting SiO₂-RAFT@PMSA nanoparticles demonstrated low detection limit (10 fmol) and high recovery yield (over 88%) for glycopeptide enrichment from tryptic digest of human IgG. The SiO₂-RAFT@PMSA nanoparticles were further applied for the analysis of mouse liver glycoproteome, a total number of 303 unique N-glycosylation sites corresponding to 185 glycoproteins was reliably profiled in three replicate nano-LC–MS/MS runs. Significantly, more glycopeptides were identified than those of nanoparticles, monolayer MSA molecules modified SiO₂@single-MSA and nonuniform multi-layer PMSA brushes coated SiO₂@PMSA, as well as commercial ZIC@HILIC beads and Click Maltose beads. The excellent performance of SiO₂-RAFT@PMSA nanoparticles results from the non-fouling property, a large quantity of functional molecules and suitable link arms provided by uniform PMSA brushes, as well as efficient interaction between glycopeptides and uniform PMSA brushes. It is concluded that the synthesized SiO₂-RAFT@PMSA nanoparticles exhibit great potential in glycoproteome analysis. Moreover, this strategy to modify nanopaticles with uniform polymer brushes via RAFT polymerization can also be explored to design other types of materials for bioseparation application.     

Highly crystalline anisotropic superstructures via magnetic field induced nanoparticle assembly

A magnetic field is successfully utilized to induce the fabrication of size controllable one-dimensional (1-D) supercrystals which are composed of a highly crystalline assembly of fcc-packed cobalt nanoparticles; the anisotropy associated supercrystal magnetism is enhanced with four times higher coercivity than that of randomly aggregated nanoparticles.     

Caspase-3 controlled assembly of nanoparticles for fluorescence turn on

A caspase-3 controlled condensation was applied to self-assemble biotinylated nanoparticles for capturing FITC-labelled streptavidin and subsequently turning on the fluorescence signal.     

Preparation of Cu nanoparticles with controlled particle size and distribution via reaction temperature and sonication

This paper presents metallic copper nanoparticles (CuNPs) that differ according to the process parameters used, such as bath temperature and sonication. The effect of different reactions on the size and distribution of CuNPs that had been formed in ethylene glycol solvent were characterized by the X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses after extraction from the solvent. The optimal dimensional properties, including size, distribution, and agglomeration, of CuNPs were determined by controlling the reaction temperature. On the other hand, the mechanically induced sonication process enhances the formation of the selective CuNPs because of the many homogeneous interactions among precursors, reducing agents, and capping agents related to the nucleation and growth of CuNPs. The mechanics of the origin of the diverse CuNPs of different size and distribution are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of large monodispersed spherical silica particles using seed particle growth

To obtain large-sized, monodispersed spherical particles of silica by sol precipitation, a seed particle growth method was attempted. The formation of secondary particles during seed particle growth causing a multimodal distribution of particle size was suppressed via fine adjustment of the reaction conditions, such as TEOS, ammonia, and water concentrations, as well as operational conditions such as feeding time and agitation speed. Among the reaction conditions, an increase of TEOS concentration promoted secondary particle formation, resulting in bimodal particle distribution. However, secondary particle formation was depressed with increasing ammonia and water concentrations. In addition, long feeding time (low feed flow rate) and rigorous agitation significantly reduced secondary particle formation because they contributed to the slow generation of supersaturation and rapid seed particle growth, respectively.     

Synthesis of narrowly distributed polystyrene-encapsulated silica nanoparticles via emulsion polymerization

Polystyrene (PS)-encapsulated silica nanoparticles were successfully synthesized by conventional emulsion polymerization for solving the aggregation matter of nanoscaled silica. The grafting coupling agents and PS on the silica surface were detected by Fourier Transform Infrared (FTIR) spectroscopy. The influence of silica and monomer to water ratios and initiator concentration on particle size distribution of the nanocomposite latex was investigated. The particle size distribution firstly narrowed and then broadened with the increase of silica and monomer to water ratios and initiator concentration. The narrow distribution could be controlled in an appropriate silica and monomer to water ratio and an initiator concentration of 1/15 and 2 wt%, respectively. From the evaluation of transmission electron microscopy (TEM) micrographs and dynamic light scattering (DLS) measurement, it was proved that the nanocomposite latex did not have all sphere-like shape, but contained tiny amounts of irregular bodies. The formation mechanism of PS-encapsulated silica nanoparticles was also discussed.     

Synthesis of well-defined, polymer-grafted silica nanoparticles via reverse ATRP

The surface grafting onto ultrafine silica via reverse ATRP of methyl methacrylate initiated by peroxide groups introduced onto the surface and conventional ATRP of Styrene initiated by the hybrid nanoparticles were investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polymer layer. The polymerization was closely controlled in solution at quite low temperature such as 70 °C. In both cases, linear kinetic plots, linear plots of molecular weight (M_n) versus conversion, in hydrodynamic diameter with increasing conversion, and narrow molecular weight distributions (M_w/M_n) for the grafted polymer samples were observed. Hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved polymer using GPC. Ultrathin films of hybrid nanoparticles were examined using TEM and AFM.     

Preparation and controlled self-assembly of Janus magnetic nanoparticles

Janus magnetic nanoparticles (~20 nm) were prepared by grafting either polystyrene sodium sulfonate (PSSNa) or polydimethylamino ethylmethacrylate (PDMAEMA) to the exposed surfaces of negatively charged poly(acrylic acid) (PAA)-coated magnetite nanoparticles adsorbed onto positively charged silica beads. Individually dispersed Janus nanoparticles were obtained by repulsion from the beads on reversal of the silica surface charge when the solution pH was increased. Controlled aggregation of the Janus nanoparticles was observed at low pH values, with the formation of stable clusters of approximately 2-4 times the initial size of the particles. Cluster formation was reversed, and individually dispersed nanoparticles recovered, by restoring the pH to high values. At intermediate pH values, PSSNa Janus nanoparticles showed moderate clustering, while PDMAEMA Janus nanoparticles aggregated uncontrollably due to dipolar interactions. The size of the stable clusters could be controlled by increasing the molecular weight of the grafted polymer, or by decreasing the magnetic nanoparticle surface availability for grafting, both of which yielded larger cluster sizes. The addition of small amounts of PAA-coated magnetic nanoparticles to the Janus nanoparticle suspension resulted in a further increase in the final cluster size. Monte Carlo simulation results compared favorably with experimental observations and showed the formation of small, elongated clusters similar in structure to those observed in cryo-TEM images.     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

Preparation of ultrathin coating layers using surface modified silica nanoparticles

Silica nanoparticles are used in various applications including catalysts, paints and coatings. To reach an optimal performance via stability and functionality, in most cases, the surface properties of the particles are altered using complex procedures. Here we describe a simple method for surface modification of silica nanoparticles (SNP) using sequential adsorption of oppositely charged components. First, the SNPs were made cationic by adsorption of a cationic polyelectrolyte. Poly(allylamine hydrochloride) (PAH) and polyethyleneimine (PEI) were chosen as polycations to investigate the difference between a linear and a branched polyelectrolyte. Next, the dispersion of cationic SNPs was combined with an anionic alkyl ketene dimer (AKD) emulsion. Using this approach cationic, hydrophobic silica particle dispersions were produced. Dynamic light scattering, contact angle measurements and atomic force microscopy (AFM) were used for analyzing the particle and coating layer properties. The chosen polyelectrolyte affected the structure of the dispersion. The layer build-up was studied in detail using a quartz crystal microbalance with dissipation monitoring (QCM-D). The adsorption and layer properties of the cationic polyelectrolytes adsorbed on silica as well as the affinity of AKD to this layer were explored. The application possibilities of the modified particle dispersions were demonstrated by preparing paper and silica surfaces with tailored properties, such as elevated surface hydrophobicity, using an ultrathin coating layer.