Synthesis,characterization and bactericidal activity of silica/silver core–shell nanoparticles

Silica/silver core–shell nanoparticles (NPs) were synthesized by coating silver NPs on silica core particles (size ~300 ± 10 nm) via electro less reduction method. The core–shell NPs were characterized for their structural, morphological, compositional and optical behavior using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–Visible spectroscopy, respectively. The size (16–35 nm) and loaded amount of silver NPs on the silica core were found to be dependent upon reaction time and activation method of silica. The bactericidal activity of the NPs was tested by broth micro dilution method against both Bacillus subtilis (gram positive) and Escherichia coli ATCC25922 (gram negative) bacterium. The bactericidal activity of silica/silver core–shell NPS is more against E. coli ATCC25922, when compared to B. subtilis. The minimal inhibitory concentration of the core–shell NPs ranged from 7.8 to 250 μg/mL and is found to be dependent upon the amount of silver on silica, the core. These results suggest that silica/silver core–shell NPs can be utilized as a strong substitutional candidate to control pathogenic bacterium, which are otherwise resistant to antibiotics, making them applicable in diverse medical devices.     

Structure,swelling, and drug release of thermoresponsive poly(amidoamine) dendrimer–poly(N-isopropylacrylamide) hydrogels

Functional drug delivery systems are important for improved pharmacotherapy. The aim of this work was to describe how the introduction of varying amounts of the dendrimer polyamidoamine (PAMAM) into a chemically cross-linked thermoresponsive poly(N-isopropylacrylamide) (PNIPAAM) gel affects the structure, swelling properties, and drug release characteristics. The structure of the gel system was characterized by small-angle X-ray scattering (SAXS), while the drug delivery system was characterized by measuring the swelling, loading, and release of the model drug. The SAXS results suggest that the PNIPAAM gel is heterogeneous on a local length scale, whereas more homogeneous gels are formed in the presence of PAMAM. Increased swelling and loading capacity were observed for higher fractions of PAMAM dendrimer. This was explained by the enhanced hydrophilicity obtained by inclusion of the dendrimers. The swelling process was observed to be very slow taking place over several days, indicating other mechanisms than diffusion to be the rate-limiting step. The temperature-induced deswelling was more pronounced for the dendrimer-containing formulations. This process was observed to be very fast and complete within a couple of hours. Similarly the release rate was quite fast without being affected by inclusion of the dendrimer. Retention of a significant portion of the loaded drug at specific conditions was shown to be due to the hydrogen bonding ability of PNIPAAM. Improved conditions for drug delivery were achieved in several respects by incorporation of PAMAM dendrimer molecules in the PNIPAAM hydrogel. Our results indicate that the PAMAM entities expand the PNIPAAM gel and that the gel becomes more homogeneous.     

Synthesis and characterization of core–shell nanoparticles and their influence on the mechanical behavior of acrylic bone cements

Core–shell nanoparticles consisting of polybutyl acrylate (PBA) rubbery core and a polymethyl methacrylate (PMMA) shell, with different core–shell ratios, were synthesized in order to enhance the fracture toughness of the acrylic bone cements prepared with them. It was observed by TEM and SEM that the core–shell nanoparticles exhibited a spherical morphology with ca. 120 nm in diameter and that both modulus and tensile strength decreased by increasing the PBA content; the desired structuring pattern in the synthesized particles was confirmed by DMA. Also, experimental bone cements were prepared with variable amounts (0, 5, 10 and 20 wt.%) of nanoparticles with a core–shell ratio of 30/70 in order to study the influence of these nanostructured particles on the physicochemical, mechanical and fracture properties of bone cements. It was found that the addition of nanostructured particles to bone cements caused a significant reduction in the peak temperature and setting time while the glass transition temperature (T_g) of cements increased with increasing particles content. On the other hand, modulus and strength of bone cements decreased when particles were incorporated but fracture toughness was increased.     

Synthesis and characterization of core∕shell Fe(3)O(4)∕ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.     

Preparation, characterization, and fluorescence properties of well-dispersed core–shell CdS/carbon nanoparticles

The core–shell CdS-carbon (CdS/C) nanoparticles were synthesized for the first time via a facile pyrolysis approach of bis(β-mercaptoethanol)-cadmium(II) as a single-source precursor. After using acid treatment method, well-dispersed and homogeneous core–shell CdS/C nanoparticles were obtained. The morphology, structure, and properties of CdS/C nanoparticles were investigated by X-ray diffraction (XRD), Raman spectra, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and fluorescence spectroscopy. Most of the prepared nanoparticles presented core–shell structures with core diameter of ~10 nm and shell thickness of ~4 nm. The CdS core belonged to hexagonal crystal system. The carbon shell was employed as a good dispersion medium to form well-dispersed small sized CdS particles. XRD and XPS results revealed that there is an interaction between CdS core and carbon shell. Fluorescence measurement showed that the monodispersed CdS-carbon nanoparticles exhibit remarkable fluorescence enhancement effect compared with that of the pristine CdS nanoparticles, which indicates the prepared nanoparticles are a promising photoresponsive material.     

Synthesis of Au@CdS core–shell nanoparticles and their photocatalytic capacity researched by SERS

High-quality Au@CdS core–shell nanoparticles (CSNs) have been synthesized to improve photo-conversion efficiency in photocatalysis. They demonstrate higher photocatalytic activity in the experiment of photocatalytic degradation of rhodamine 6G (R6G) solution than that of CdS counterparts. Au@CdS CSNs can broaden the absorption range in visible region compared to CdS counterparts. The heterojunction interface between Au and CdS facilitates the separation of photo-generated electron–hole pairs, and transfers electrons from CdS region to Au core. The two advantages are crucial to improve the photocatalytic activity of Au@CdS CSNs. Charge transfer mechanism between metal and semiconductor is efficient that can be used to guide the design of photocatalysts, photovoltaics, and other optoelectronic devices to effectively utilize the solar power. In this paper, we research the photocatalytic process by surface-enhanced Raman scattering (SERS). The combination of photocatalysis and SERS not only can show the change in concentration of R6G solution, but also can provide the information of the change of R6G molecular structure in photocatalytic process.     

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

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

Synthesis and characterization of chitosan–carbon nanotube composites

Acid functionalized single walled carbon nanotubes were covalently grafted to chitosan by first reacting the oxidized carbon nanotubes with thionyl chloride to form acyl-chlorinated carbon nanotubes which are subsequently dispersed in chitosan and covalently grated to form composite material, CNT–chitosan, 1, which was washed several times to remove un-reacted materials. This composite has been characterized by FTIR, 13C NMR, TGA, SEM and TEM and has been shown to exhibit enhanced thermal stability. The reaction of 1, with poly lactic acid has also been accomplished to yield CNTchitosan–g-poly(LA), 2 and fully characterized by the above techniques. Results showed covalent attachment of chitosan and chitosan–poly lactic acid to the carbon nanotubes.     

Controllable synthesis and characterization of Ag@AgBr core–shell nanowires

Ag@AgBr core–shell nanowires have been synthesized in large quantities via a redox reaction between Ag nanowires and FeBr₃ in solution at room temperature. The effect of the molar ratio of Fe:Ag on the formation and optical absorption of the Ag@AgBr core–shell nanowires was systematically studied. The results showed that Ag nanowires were converted into Ag@AgBr core–shell nanowires and finally into AgBr nanorods with the increase of the molar ratio of Fe:Ag. At the same time, the optical absorption of Ag nanowires decreased gradually and disappeared finally. In addition, the growth mechanism of the Ag@AgBr core–shell nanowires was also discussed in detail.     

Development of electrosprayed artesunate-loaded core–shell nanoparticles

Objective: Artesunate (ART) is proven to have potential anti-proliferative activities, but its instability and poor aqueous solubility limit its application as an anti-cancer drug. The present study was undertaken to develop coaxial electrospraying as a novel technique for fabricating nanoscale drug delivery systems of ART as the core–shell nanostructures.

Methods: The core–shell nanoparticles (NPs) were fabricated with coaxial electrospraying and the formation mechanisms of NPs were examined. The physical solid state and drug–polymer interactions of NPs were characterized by X-ray powder diffraction (XRPD) and Fourier transform infrared (FTIR) spectroscopy. The effects of materials and electrospraying process on the particle size and surface morphology of NPs were investigated by scanning electron microscopy (SEM). The drug release from NPs was determined in vitro by a dialysis method.

Results: The ART/poly(lactic-co-glycolic) acid (PLGA) chitosan (CS) NPs exhibited the mean particle size of 303?±?93?nm and relatively high entrapment efficiency (80.5%). The release pattern showed an initial rapid release within two hours followed by very slow extended release. The release pattern approached the Korsmeyer–Peppas model.

Conclusions: The present results suggest that the core–shell NPs containing PLGA and CS have a potential as carriers in the anticancer drug therapy of ART.     

Host-guest interaction and nano-microstructure of spherical poly(amidoamine) dendrimer/gold hybrid colloids under γ-ray irradiation

This investigation shows that in absence of the chemical reductant and the other protective reagents, the host-guest interaction and the molar ratio of dendrimers/Au³⁺ other than size and shape of the templates play an important role for the preparation of stable gold hybrid colloids by ⁶⁰Co γ-ray irradiation using spherical PAMAM-G5 as nonlinear polymeric template. The hybrid colloid resultants comprised of the ordered nano-crystal and the random non-crystal part, which has been confirmed by HRTEM, display spherical structure and the polydispersity of the size distribution in the range of nanometer scale. The dendrimer/gold hybrid colloids are formed by the intramolecular and intermolecular adsorption action between PAMAM-G5 template and gold nanoparticles, respectively.     

Synthesis and characterization of silica–lead sulfide core–shell nanospheres for applications in optoelectronic devices

Nanoscale miniaturization of chalcogenide semiconductors such as lead sulfide (galena) can generate interesting quantum confinement effects in the field of optoelectronic applications. In this work, we developed a process in order to obtain SiO₂ nanospheres coated with Galena, as the denominated core–shell system; this process is based on Stöber’s method, where the magnetic stirring was replaced by an ultrasonic bath to achieve well rounded and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. The nanostructures’ chemical composition, morphology, and optical properties were determined by transmission electron microscopy and UV–Vis spectroscopy. As a result, the nanoshells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nanoshell also shown an optical spectrum shift toward blue and a remarkable increase of 3.75 eV in its band gap, compared with the PbS bulk value. The chemical composition is studied by energy scattering spectroscopy and X-ray photoelectron spectroscopy analysis.

     

Synthesis,structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO₂) and Zinc oxide (ZnO) as well as Silica (SiO₂) coated ZrO₂ core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO₂ on ZrO₂@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO₂) and the shell materials (ZnO and SiO₂) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.     

Bi-layered polymer–magnetite core/shell particles: synthesis and characterization

Polymer magnetic core particles receive growing attention due to these materials owing magnetic properties which are widely used in different applications. The prepared composite particles are characterized with different properties namely: a magnetic core, a hydrophobic first shell, and finally an external second hydrophilic shell. The present study describes a method for the preparation of bi-layered polymer magnetic core particles (diameter range is 50–150 nm). This method comprises several steps including the precipitation of the magnetic iron oxide, coating the magnetite with oleic acid, attaching the first polymer shell by miniemulsion polymerization and finally introducing hydrophilic surface properties by condensation polymerization. The first step is the formation of magnetite nanoparticles within a co-precipitation process using oleic acid as the stabilizing agent for magnetite. The second step is the encapsulation of magnetite into polyvinylbenzyl chloride particles by miniemulsion polymerization to form a magnetic core with a hydrophobic polymer shell. The hydrophobic shell is desired to protect magnetite nanoparticles against chemical attack. The third step is the coating of magnetic core hydrophobic polymer shell composites with a hydrophilic layer of polyethylene glycol by condensation polymerization. Regarding the miniemulsion polymerization the influence of the amount of water, the mixing intensity and the surfactant concentration were studied with respect to the formation of particles which can be further used in chemical engineering applications. The resulting magnetic polymer nanoparticles were characterized by particle size measurement, chemical stability, iron content, TEM, SEM, and IR.     

Novel and simple route for the synthesis of core–shell chitosan–gold nanocomposites

This work presents a novel and simple route for the synthesis of water-soluble core–shell chitosan–gold nanocomposites. The experimental procedure can be summarized by the following steps: (i) chitosan deacetylation, (ii) chitosan depolymerization, (iii) chitosan nanoparticles’ formation and (iv) chitosan–gold nanocomposite formation. FT-IR spectroscopic results indicate that the formation of chitosan nanoparticles (ChtNPs) occurs via NH₃⁺ and PO⁻ groups electrostatic interactions, while UV–vis spectra points to a possible embedding of gold nanoparticles into the ChtNPs. This feature was confirmed by electronic transmission microscopy measurements. Chitosan and gold are biocompatible materials. Added to this, the obtained chitosan–gold nanocomposites presented thermal and absorbance properties which strongly point to their potential use in phototherapeutic processes.     

Ascorbic acid-mediated synthesis and characterisation of iron oxide/gold core–shell nanoparticles.

The current article reports on providing surface modification of magnetic nanoparticles with gold to provide stability against aggregation. Gold-coated magnetite nanoparticles were synthesised to combine both magnetic as well as surface plasma resonance (SPR) properties in a single moiety. The nanocomposites were produced by reduction (using ascorbic acid) of gold chloride on to the surface of iron oxide nanoparticles. Ascorbic acid not only acts as a reducing agent, but also the oxidised form of ascorbic acid i.e. Dehydro-ascorbic acid acts as a capping agent to impart stability to as synthesised gold-coated iron oxide nanocomposites. The synthesised nanocomposite was monodispersed with a mean particle size of around 16 nm and polydispersity index of 0.190. X-ray diffraction analysis confirms presence of gold on the surface of magnetite nanoparticles. The synthesised nanocomposites had a total organic content of around 3.2% w/w and also showed a shifted SPR peak at 546 nm as compared to gold nanoparticles (528 nm). Both uncoated and gold-coated magnetite exhibited superparamagnetic behaviour at room temperature. Upon coating with gold shell, saturation magnetisation of iron oxide nanoparticles decreases from 42.806 to 3.54 emu/gram.     

Synthesis of Al/Fe3Al core–shell intermetallic nanoparticles by chemical liquid deposition method

In this work, an Al/Fe₃Al core–shell nanoparticle was obtained by heat treatment of a precursor in high purity of argon. The precursor, with Fe(CO)₅ and nano Al as raw materials, was synthesized simply by a chemical liquid deposition method. The evolution of the phase and morphology during the heat-treatment has been carefully studied by XRD and TEM. The results indicate that the precursor transformed to core–shell structure of Fe₃Al intermetallic nanoparticle. The formation of the Fe₃Al intermetallic nanoparticle was explored by DSC test, which reveals that the formation temperature of the nanoparticle is around 587 °C. Moreover, the TG–DSC measurements from 50 °C to 1000 °C in compressed air (20% O₂ and 80% N₂) reveal that the heat-treated powder of the precursor remains thermal stability in relatively low temperature but becomes concentrated combustion in elevated temperature.