Multilayer Nanoparticles Research Articles

Effect of Liquid Media on the Formation of Multi-Layer Graphene-Synthesized Metal Particles.

We report a simple approach for the production of copper nanoparticles by a wire explosion process that creates different structures in deionized (DI) water versus isopropyl alcohol (IPA) liquid media. In DI water, copper nanoparticles (CNs) are formed, while multi-layer graphene-synthesized copper nanoparticles (MGCNs) with a high degree of graphitization are formed in the IPA liquid media. The nanoparticles have an average diameter ranging from 10 nm to 300 nm and a quasi-spherical morphology. The morphologies and sizes of nanoparticles formed via this method were characterized by high-resolution transmission electron microscopy (HRTEM), field-emission scattering electron microscopy (FESEM), and analysis of dynamic light scattering (DLS). The microstructures and chemical bonding of the nanoparticles were studied by X-ray diffraction (XRD), Raman spectra measurement, and X-ray photoelectron spectroscopy (XPS). This results show an easily reproducible way to synthesize metal-core nanoparticles with multi-layer graphene shells based onto the liquid media used during synthesis. These materials can be used in the field of energy storage and as additives in the near future.

Europium(III)-Doped ZnO Obtained by a Hierarchically Nanostructured Multilayer Growth Strategy

A layer-by-layer growth method, named herein as impregnation–decomposition cycles (IDCs), was used to build hierarchically nanostructured multilayered nanoparticles, alternating undoped ZnO and Eu(...

Sol–gel-based single and multilayer nanoparticle thin films on low-temperature substrate poly-methyl methacrylate for optical applications

Single and multilayer (SiO2, TiO2, SiO2–TiO2, TiO2/SiO2–TiO2/SiO2) films were deposited on polymer substrate poly-methyl methacrylate (PMMA) at room temperature by sol–gel method. Optical micrographs show that spin-coated nanoparticle thin films have homogeneous surface with good adhesion with PMMA substrate. Scanning electron microscope results show good incorporation of silica and titania particles as composites with small grain size within range of 0.2–1.28 µm. The structural characterization was carried out by X-ray diffraction, which shows an amorphous pattern for SiO2, SiO2–TiO2 and TiO2/SiO2–TiO2/SiO2 samples but shows semicrystalline behavior in TiO2 sample. From UV–visible spectroscopy, it is found that coated films have a good optical transparency with tunable refractive index of 1.39–2.14. So, these films can be useful for various potential optical applications.

Magnetically Multilayer Polysaccharide Membranes for Biomedical Applications.

Self-standing nanocomposite films based on biopolymers and functional nanostructures have been widely used due to their potential applications as active elements in biomedical devices. The coupling between chitosan (CHI) and alginate (ALG) multilayered films and magnetic nanoparticles (MNPs) allowed to fabricate magnetic responsive freestanding membranes with a high structural control along the thickness, using the layer-by-layer (LbL) methodology. The mechanical characterization evidenced a trend for an increase of both Young modulus, and ultimate tensile strength with the inclusion of MNPs, or by cross-linking with genipin. Additionally, the multilayered membranes exhibited shape memory properties triggered by hydration. The in vitro biological performance studies showed that cells were more viable and adherent with higher proliferation rates when MNPs were included in the membranes. Our results suggested the potential of the developed magneto-active freestanding membranes for biomedical applications, such as in tissue engineering and biomedical applications.

Hydrothermal synthesis of 3D disulfide nanoparticles molybdenum / carbon

The results of the synthesis of 3D multilayer nanoparticles of molybdenum disulfide / carbon by hydrothermal synthesis with the use of cetyltrimethylammonium cation as micelles are presented in the paper. The elemental composition, structural and morphological properties of the obtained materials were investigated by X-ray diffractometry, transmission electron microscopy, energy-dispersive X-ray spectrometry and adsorption porometry. The synthesized nanoparticles, preferably spherical in shape with an average size of 40-70 nm, have been found to have a doublet-hierarchical structure in which 2H-MoS2 layers alternate with carbon layers (atomic ratio of about 1: 1). Annealing at a temperature of 500 ° C in an argon atmosphere leads to the destruction of nanospheres, but does not change the atomic Mo: S ratio.

Multilayered Nanoparticles for Gene Delivery Used to Reprogram Human Foreskin Fibroblasts to Neurospheres.

Polycationic nanocomplexes are a robust means for achieving nucleic acid condensation and efficient intracellular gene deliveries. To enhance delivery, a multilayered nanoparticle consisting of a core of electrostatically bound elements was used. These included a histone-mimetic peptides, poly-l-arginine and poly-d-glutamic acid was coated with silicate before surface functionalization with poly-l-arginine. Transfection efficiencies and duration of expression were similar when using green fluorescent protein (GFP) plasmid DNA (pDNA) or GFP mRNA. These nanoparticles demonstrated significantly higher (>100%) and significantly longer (15 vs. 4 days) transfection efficiencies in comparison to a commercial transfection agent (Lipofectamine 2000). Reprogramming of human foreskin fibroblasts using mRNA to the Sox2 transcription factor resulted in three-fold higher neurosphere formation in comparison to the commercial reagent. These results demonstrate the potential of these nanoparticles as ideal vectors for gene delivery.

Multilayer graphene–gold nanoparticle hybrid substrate for the SERS determination of metronidazole

In this paper, a simple, quick and reproducible SERS substrate combining the properties of multilayer graphene (≈4 layers) and gold nanoparticles has been developed. The Raman signal of metronidazole is enhanced at a factor of 124 when deposited on the hybrid substrate enabling its determination at low concentrations. The five most relevant added values of the paper as regards other similar proposed procedures are: i) better sensibility, ii) good reproducibility, iii) rapidity, iv) reusability and v) instrumental simplicity. The procedure presented is capable of detecting and quantifying small quantities of metronidazole without implying any preconcentration step, just using an affordable and portable Raman spectrometer. The LOD and LOQ achieved with this hybrid substrate were 1.1 and 3.68mgL−1 of the analyte. The use of graphene provides high reproducibility to the SERS active hybrid substrate. The RSD was 7.76% within a substrate and 10.92% between substrates. The developed SERS active hybrid substrate can be reused without loss in sensitivity.

Cu(III)-independent oxidation and sensing of glucose on multi-layer stacked copper nanoparticles

A highly sensitive electrode for sensing glucose has been fabricated by electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole on a solid carbon paste substrate, and subsequent electrodeposition of multi-layer stacked copper particles as an outer surface. The individual copper particles are characterized by a large number of edges and corners of crystallites. Their preferred orientation {111} is parallel to the electrode surface. The conductive polymer interlayer results in an increase of the particle nucleation density and a further decrease of the polarization overpotential for direct (enzyme-free) oxidation of glucose in 0.1 M NaOH solution. A well-shaped voltammetric peak can be observed at around 0.3–0.5 V (vs. SCE, depending on scan rate) that is due to glucose oxidation. This potential is much lower than the one required for Cu(III) formation. A bulk electrolysis experiment using a thin-layer electrochemical cell confirmed the assumption that that glucose undergoes 2-electron oxidation. The mechanism of glucose oxidation in the absence of Cu(III) is discussed. The electrode exhibits a very high sensitivity (slope) of 3.31 mA cm−2 mM−1, and the detection limit is 2 μM (at an SNR of 3). Features of the new sensor include the ease of fabrication, its high stability and good selectivity.

Multi-layered polymeric nanoparticles for pH-responsive and sequenced release of theranostic agents.

In this study, multi-layered pH-responsive polymeric nanoparticles (NPs) are prepared by multiple (up to 4) emulsifications to encapsulate multiple hydrophilic and hydrophobic theranostic agents for controlled and sequenced release. It is found that the sequence of release of multiple chemotherapeutic agents from the NPs significantly affects their efficacy against cancer cells.

High temperature continuous flow synthesis of CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS nanocrystals.

Continuous flow reactors show great promise for large-scale synthesis of quantum dots. Here, we discuss results for the synthesis of multi-layered Cd-based hybrid nanocrystals - CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS - in a continuous flow reactor. The simple reactor design and liquid-phase chemistry obviate the need for preheating or in-line mixing, and the chosen reactor dimensions and operating conditions allow for high flow rates (∼10 mL min(-1)). Additionally, the simple reactor design is well suited for scale-up. The CdSe/CdS/ZnS particles synthesized at elevated temperatures in the reactor exhibit quantum yields of over 60% at longer wavelengths (red region). The shell growth for these particles is conducted without the need for complex dropwise addition or SILAR shell growth procedures used in batch reactors. CdS-based particles were shown to have a higher performance when using octadecene-S instead of TOP-S, which improved the quality of shell growth. In addition, stoichiometric synthesis of the alternate CdSeS/ZnS alloy particles was conducted, removing the need for a large excess of S to offset the lower S reactivity. CdSeS/ZnS alloy nanoparticles exhibit quantum yields of about 50% in the intermediate wavelength range (500-600 nm).

Colorimetric plasmon sensors with multilayered metallic nanoparticle sheets.

Colorimetric plasmon sensors for naked-eye detection of molecular recognition events have been proposed. Here, 3-layered Ag nanoparticle (NP) sheets on a Au substrate fabricated using the Langmuir-Schaefer method were utilized as the detection substrates. A drastic color change was observed following the binding of Au NPs via avidin-biotin interactions at less than 30% surface coverage. The color change was attributed not only to the localized surface plasmon resonance (LSPR) of the adsorbed Au NPs but also to the multiple light trapping effect derived from the stratified Au and Ag NPs, as predicted by a finite-difference time-domain (FDTD) simulation. This plasmonic multi-color has great potential in the development of simple and highly sensitive diagnostic systems.

Multilayer fluorescent magnetic nanoparticles with dual thermoresponsive and pH-sensitive polymeric nanolayers as anti-cancer drug carriers

Fluorescent magnetic nanoparticles with dual thermoresponsive and pH-sensitive polymeric nanolayers as anti-cancer drug carriers.

Facile synthesis of N-halamine-labeled silica-polyacrylamide multilayer core-shell nanoparticles for antibacterial ability.

Silica-polymer antimicrobial composites with a core-shell nanostructure are often prepared through a polymeric process. However, it is difficult to control the polymerization degree of the polymers to give a uniform size distribution. In this article, we present a facile approach to produce antimicrobial silica@polyacrylamide (SiO2@PAM) core-shell nanoparticles, which were synthesized via an electrostatic self-assembly method using acyclic N-halamine polymeric polyacrylamide. The morphologies and structures of these as-prepared nanoparticles were characterized by different techniques. And their antibacterial performance against both Gram-positive bacteria and Gram-negative bacteria was also evaluated. Based on the preliminary results, these core-shell nanosized spheres were made of an outer polymer shell which decorated the inner SiO2 core, showing the encapsulation of silica nanoparticles with PAM polymers. After chlorination, the resultant nanosized particles displayed a powerful and stable bactericidal capability toward both of the two model bacterial species. Bactericidal assessment further suggested a coordinated effect of the well-known antibacterial performance of N-halamines and the flocculation of PAM on the antibacterial behavior. The in vitro cytotoxicity of the prepared nanoparticles with varying concentrations was studied using mouse fibroblast cells (L929). The CCK-8 assay revealed that the SiO2@PAM composites possessed a non-cytotoxic and favorable response to the seeded cells in vitro. These results indicate the suitability of the SiO2@PAM composite particles for controlling biocidal activity, demonstrating their potential applications in deactivating bacteria or even disease control.

Formation of self-assembled multi-layer stable palladium nanoparticles for ligand-free coupling reactions

SAPD works for ligand-free Buchwald–Hartwig reaction and Suzuki–Miyaura coupling with low-leaching (<1 ppm) and high recyclability (>10 times).

Evaluation of multilayer coated magnetic nanoparticles as biocompatible curcumin delivery platforms for breast cancer treatment

A novel biocompatible multi-layer iron oxide magnetic nanoparticles with sustained sensitive release profile, and improved cellular uptake.

Designing multilayered nanoplatforms for SERS-based detection of genetically modified organisms

In this study, the multilayered surface-enhanced Raman spectroscopy (SERS) platforms were developed for the analysis of genetically modified organisms (GMOs). For this purpose, two molecules [11-mercaptoundecanoic acid (11-MUA) and 2-mercaptoethylamine (2-MEA)] were attached with Aurod and Auspherical nanoparticles to form multilayered constructions on the gold (Au)slide surface. The best multilayered platform structure was chosen depending on SERS enhancement, and this surface was characterised with atomic force microscopy (AFM) and attenuated total reflectance Fourier transform infrared spectroscopy. After the optimum multilayered SERS platform and nanoparticle interaction was identified, the oligonucleotides on the Aurod nanoparticles and Auslide were combined to determine target concentrations from the 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) signals using SERS. The correlation between the SERS intensities for DTNB and target concentrations was found to be linear within a range of 10 pM to 1 µM, and with a detection limit of 34 fM. The selectivity and specificity of the developed sandwich assay were tested using negative and positive controls, and nonsense and real sample studies. The obtained results showed that the multilayered SERS sandwich method allows for sensitive, selective, and specific detection of oligonucleotide sequences.

Preparation of ZrO2-Silica Microspheres by Layer-by-Layer Self-Assemble Technique

The uniform nanoparticle multilayers micrometer-sized silica particle have been fabricated by consecutively assembling of surfactant C12H25SO4Na (SDS) and nanoparticles onto Silica microspheres and subsequently removing the surfactant by calcinations. The samples were characterized by X-ray diffraction, FT-IR,TG and SEM. Presence of the FT-IR bands with frequencies ranging from 800 to 900 cm-1 can be assigned to Si–O vibration, and to Zr–O–Si stretching vibration. XRD analysis showed obviously the characteristic diffraction peaks of tetragonal (T-ZrO2) and nanoscale of ZrO2. The SEM image showed that the surface layers of silica microspheres were coated by nanoparticles.

Dimensionality-dependent charge transport in close-packed nanoparticle arrays: from 2D to 3D.

Charge transport properties in close-packed nanoparticle arrays with thickness crossing over from two dimensions to three dimensions have been studied. The dimensionality transition of nanoparticle arrays was realized by continually printing spatially well-defined nanoparticle monolayers on top of the device in situ. The evolution of charge transport properties depending on the dimensionality has been investigated in both the Efros-Shaklovskii variable-range-hopping (ES-VRH) (low temperature) regime and the sequential hopping (SH) (medium temperature) regime. We find that the energy barriers to transport decrease when the thickness of nanoparticle arrays increases from monolayer to multilayers, but start to level off at the thickness of 4–5 monolayers. The energy barriers are characterized by the coefficient βD at ES-VRH regime and the activation energy Ea at SH regime. Moreover, a turning point for the temperature coefficient of conductance was observed in multilayer nanoparticle arrays at high temperature, which is attributed to the increasing mobility with decreasing temperature of hopping transport in three dimensions.

Preparation and Characterization of Silver Liquid Thin Films for Magnetic Fluid Deformable Mirror

Silver liquid thin film, formed by silver nanoparticles stacking and spreading on the surface of the liquid, is one of the important parts of magnetic fluid deformable mirror. First, silver nanoparticles were prepared by liquid phase chemical reduction method using sodium citrate as reducing agent and stabilizer and silver nitrate as precursor. Characterization of silver nanoparticles was studied using X-ray diffractometer, UV-vis spectrophotometer, and transmission electron microscope (TEM). The results showed that silver nanoparticles are spherical and have a good monodispersity. Additionally, the effect of the reaction conditions on the particle size of silver is obvious. And then silver liquid thin films were prepared by oil-water two-phase interface technology using as-synthesized silver nanoparticles. Properties of the film were investigated using different technology. The results showed that the film has good reflectivity and the particle size has a great influence on the reflectivity of the films. SEM photos showed that the liquid film is composed of multilayer silver nanoparticles. In addition, stability of the film was studied. The results showed that after being stored for 8 days under natural conditions, the gloss and reflectivity of the film start to decrease.

Quaternized chitosan mediated assembly of gold nanoparticles multilayers

Self-assembled multilayers of quaternized chitosan (QCHI) and gold nanoparticles (AuNPs) were built up on quartz and gold substrates. To evaluate the effect of the surface coverage of AuNPs on the structural, optical and electrochemical properties of multilayers prepared with different AuNPs adsorption time were compared. UV-Vis and AFM characterization indicated that AuNPs in each bilayer are spatially separated, and interparticle interactions are mainly produced between bilayers. The complex refractive index and thickness of the QCHI-AuNPs multilayers were properly determined using an anisotropic single layer model. The optical constants obtained were quite different from those of bulk gold, and their values depend on the coverage of AuNPs. The thickness per bilayer of the structures present a progressive increase as AuNP's coverage augments, reaching a value close to the nominal AuNPs diameter after 60min of adsorption. These results indicate that the interpenetration of bilayers in the structure depends on the surface concentration of AuNPs. The charge transport through the QCHI-AuNPs film was studied using different redox probes. The effects of the adsorption time of AuNPs and the number of bilayers (n) of the structure on the charge transfer rate constants, kct, were analyzed. The incorporation of AuNPs in the structure produces an increase of kct, as the adsorption time of AuNPs rise. In addition, the values of kct were independent of n, in the interval studied (up to n=5), suggesting that the electronic communication in the multilayered structure was mediated by the AuNPs.