Multilayer Nanoparticles Research Articles

Coaxial electrospray of microparticles and nanoparticles for biomedical applications

Coaxial electrospray is an electrohydrodynamic process that produces multilayer microparticles and nanoparticles by introducing coaxial electrified jets. In comparison with other microencapsulation/nanoencapsulation processes, coaxial electrospray has several potential advantages such as high encapsulation efficiency, effective protection of bioactivity and uniform size distribution. However, process control in coaxial electrospray is challenged by the multiphysical nature of the process and the complex interplay of multiple design, process and material parameters. This paper reviews the previous works and the recent advances in design, modeling and control of a coaxial electrospray process. The review intends to provide general guidance for coaxial electrospray and stimulate further research and development interests in this promising microencapsulation/nanoencapsulation process.

The multilayer nanoparticles formed by layer by layer approach for cancer-targeting therapy

The multilayer nanoparticles (NPs) were prepared for cancer-targeting therapy using the layer by layer approach. When drug-loaded Pluronic NPs were mixed with vesicles (liposomes) in the aqueous medium, Pluronic NPs were incorporated into the vesicles to form the vesicle NPs. Then, the multilayer NPs were formed by freeze-drying the vesicle NPs in a Pluronic aqueous solution. The morphology and size distribution of the multilayer NPs were observed using a TEM and a particle size analyzer. In order to apply the multilayer NPs as a delivery system for docetaxel (DTX), which is a model anticancer drug, the release pattern of the DTX was observed and the tumor growth was monitored by injecting the multilayer NPs into the tail veins of tumor (squamous cell carcinoma)-bearing mice. The cytotoxicity of free DTX (commercial DTX formulation (Taxotere®)) and the multilayer NPs was evaluated using MTT assay. We also evaluated the tumor targeting ability of the multilayer NPs using magnetic resonance imaging. The multilayer NPs showed excellent tumor targetability and antitumor efficacy in tumor-bearing mice, caused by the enhanced permeation and retention (EPR) effect. These results suggest that the multilayer NPs could be a potential drug delivery system for cancer-targeting therapy.

Independence of plasmonic near-field enhancements to illumination beam profile

Near-field enhancements of the electric field at the center of spheroidal multilayer metallic nanoparticles (NPs) are investigated when illuminated by focused beams of arbitrary field structure (i.e., amplitude, phase, and polarization distributions). Employing a Mie-type representation, the enhancement at the center of such NPs (such as a core-shell geometry) is analytically shown to be independent of the field structure of the illumination beam for both on- and off-axis NPs. Furthermore, it is shown that, to leading order, the average field enhancement in the near field of these NPs is also approximately illumination independent.

In vivo magnetic enrichment, photoacoustic diagnosis, and photothermal purging of infected blood using multifunctional gold and magnetic nanoparticles.

Bacterial infections are a primary cause of morbidity and mortality worldwide. Bacteremia is a particular concern owing to the possibility of septic shock and the development of metastatic infections. Treatment of bacteremia is increasingly compromised by the emergence of antibiotic resistant strains, creating an urgent need for alternative therapy. Here, we introduce a method for in vivo photoacoustic (PA) detection and photothermal (PT) eradication of Staphylococcus aureus in tissue and blood. We show that this method could be applicable for label-free diagnosis and treatment of in the bloodstream using intrinsic near-infrared absorption of endogenous carotenoids with nonlinear PA and PT contrast enhancement. To improve sensitivity and specificity for detection of circulating bacteria cells (CBCs), two-color gold and multilayer magnetic nanoparticles with giant amplifications of PA and PT contrasts were functionalized with an antibody cocktail for molecular targeting of S. aureus surface-associated markers such as protein A and lipoprotein. With a murine model, the utility of this approach was demonstrated for ultrasensitive detection of CBCs with threshold sensitivity as low as 0.5 CBCs/mL, in vivo magnetic enrichment of CBCs, PT eradication of CBCs, and real-time monitoring of therapeutic efficacy by CBC counting. Our PA-PT nano-theranostic platform, which integrates in vivo multiplex targeting, magnetic enrichment, signal amplification, multicolor recognition, and feedback control, could be used as a biological tool to gain insights on dissemination pathways of CBCs, infection progression by bacteria re-seeding, and sepsis development and treatment, and could potentially be feasible in humans, especially using bypass schematic.

Meso-scale modelling of shock wave propagation in a SiC/Al nanocomposite reinforced with WS2-inorganic fullerene nanoparticles

It has been postulated that nanocomposites incorporating IF-WS2 nanoparticles within a strong matrix might form the next generation of highly shock-resistant materials. The present work describes initial analyses into the shock response of such materials via a sequential multi-scale dynamic analysis. Density functional theory is used to calculate the elastic properties of the multilayered WS2 nanoparticles. These properties are then used within an explicit finite element (FE) analysis of wave propagation through an embedded statistical volume element (SVE) of a two-phase nanocomposite consisting of a matrix with IF-WS2 nanoparticles. Some wave front dispersion was noted, particularly where the modulus of the matrix is significantly different from that of the particles. A three-phase nanocomposite consisting of an aluminium matrix with IF-WS2 and SiC nanoparticles was also considered, and showed more apparent wave front dispersion than for the two-phase nanocomposite. Hugoniot shock propagation data have been derived from the simulation outputs. It is concluded that sequential multiscale modelling of these systems is appropriate and can provide useful information about shock wave propagation in the elastic region. The work also provides a foundation for more realistic simulations at higher rate loading, where it will be necessary to incorporate material failure in the models.

Tuning Colors of Silver Nanoparticle Sheets by Multilayered Crystalline Structures on Metal Substrates

We report a new concept of tuning plasmonic colors of two-dimensional crystalline silver nanoparticle sheets with layer-by-layer structures. The multilayered crystalline sheets fabricated by the Langmuir–Schaefer method keep the localized surface plasmon resonance bands at the same position (λmax = 465 nm) on quartz, while they change their colors drastically on metal substrates depending on the number of layers (one to five layers). The response of the absorption spectra was absolutely nonlinear, with maximum absorption for two or three layers. The obtained results were well reproduced by the finite difference time domain simulation. The simulation confirmed that these plasmonic colors originate not only from near-field coupling of plasmon resonance but also far-field nano-optics of the multilayered silver nanoparticle sheets.

Electrochromic Bragg Mirror: ECBM

The colloidal assembly of a nanoporous electrochromic 1D Bragg mirror comprising NiO and WO3 nanoparticle multilayers enables the convolution of electrically tunable electronic crystals and photonic crystals into a single device, providing thereby a distinctive means of creating and manipulating color.

A displacement principle for mercury detection by optical waveguide and surface enhanced Raman spectroscopy

A novel displacement principle of metal nanoparticles for target analysis, differing from the usual target-induced aggregation principle, was proved feasible by the use of para-aminothiophenol coupled Au nanoparticles (PATP-Au) multilayer as probes to detect Hg2+. The PATP-Au multilayer was fabricated through layer-by-layer assembly of Au nanoparticles on optical waveguide (OWG) chip surface using para-aminothiophenol (PATP) as coupling molecules. The localized surface plasmon resonance (LSPR) extinction from Au nanoparticles and the PATP as a Raman reporter enable to easily capture changes in PATP-Au multilayer by OWG and of surface enhanced Raman spectroscopy, respectively. The introduction of the Hg2+, which has a higher binding affinity to the thiol group of PATP, greatly destroyed the multilayer structure, and produced a large change, several folds higher than the noise, in LSPR features and Raman signals of PATP-Au multilayer probes, and resulted in an excellent selectivity for Hg2+ detection at a low level of 1nM. This investigation provides us more ideas on the future development of surface analysis techniques for the detection of various target analytes.

Plasmonic multilayer nanoparticles enhanced photocurrent in thin film hydrogenated amorphous silicon solar cells

A plasmonic-structure incorporated double layer of Au nanoparticles embedded in the transparent conducting oxide at the back-reflector of the hydrogenated amorphous silicon (a-Si:H) solar cells is demonstrated. These devices exhibit an increase of energy conversion efficiency of 18.4% and short-circuit current density of 9.8% while improving fill-factor and without sacrificing open-circuit voltage. The increase in photocurrent is correlated with the enhanced optical absorption in the cell, with improved optical-path-length by a factor of 7 at the wavelength of 800 nm, due to enhanced diffuse scattering of light through resonant plasmon excitations within Au nanoparticles. In addition to enhanced scattering, applying high-work-function Au nanoparticles can improve the work function match at TCO/a-Si:H interface.

Layer-by-Layer Assembled Multilayers of Polyethylenimine-Stabilized Platinum Nanoparticles and PEDOT:PSS as Anodes for the Methanol Oxidation Reaction

Polyethylenimine-capped platinum nanoparticles (PEI-capped Pt NPs) are synthesized by photoreduction and qualified as a component for electrostatic layer-by-layer assembly and subsequent electrocatalysis. The PEI-capped Pt NPs are characterized for size and charge using scanning force microscopy, transmission electron microscopy, dynamic light scattering and zetapotential. Well-defined multilayers are produced via thin film electrostatic assembly of PEI-capped Pt NPs with the conducting polymer: poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) [(PEDOT:PSS)(-)Na(+)]. The composite thin films are subsequently characterized by ultraviolet-visible spectroscopy, scanning force microscopy, inductively coupled plasma mass spectroscopy and thermogravimetric analysis. The layer-by-layer deposition process was found to proceed in a controlled manner which permits the fabrication of stable and uniform multilayer thin films. [PEI-capped Pt NPs/(PEDOT:PSS)] multilayers were found to be an active catalyst coating for the oxidation of methanol and a 20 bilayer film proceeds with a stable level of catalyst activity for over 1000 oxidation cycles.

Amperometric Immunosensor Based on L-Cysteine/Gold Colloidal Nanoparticles for Carbofuran Detection

In this study, anti-carbofuran monoclonal antibodies (Ab) were immobilized onto a gold electrode surface modified with multilayers of L-cysteine and gold colloidal nanoparticles (GNPs). Furthermore, horseradish peroxidase (HRP) as enzyme membrane was used for blocking unspecific sites and amplifying signal. The conformational properties of the immunosensor were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The concentration of antibody solution, pH of working buffer and incubation time were studied in detail for optimization of analytical performance. Under optimal conditions, the variation of current response was proportional to the concentration of carbofuran which ranged from 0.01 ng/mL to 50 ng/mL with a correlation coefficient of 0.9912. The detection limit was 0.01 ng/mL (S/N = 3). The proposed immunosensor exhibited good reproducibility and stability and it can be used for the rapid detection of carbofuran pesticide.

Layer by Layer Deposition of Polyethylene Glycol Capped Silver Nanoparticles/Chitosan on Polyethylene Substrate

Multilayers of silver nanoparticles and chitosan were deposited on polyethylene film by a layer-by-layer (LBL) self-assembly technique. Silver nanoparticles with a size of about 5 nm were prepared by chemical reduction and then fabricated onto a polyethylene (PE) substrate, which led to the formation of a colored film with the thicknesses of 2, 4, 8, 12, and 20 layers. Silver nanocomposites were characterized by atomic force microscopy (AFM) and UV-visible spectroscopy, X-ray diffraction (XRD), and infrared spectroscopy (FTIR). Results showed that nanoparticles deposited homogenously on the surface of the polyethylene film. LBL silver nanocomposites showed considerable antimicrobial activity by agar diffusion test.

Polyelectrolyte Multilayered Nanoparticles: Using Nanolayers for Controlled and Targeted Systemic Release

The simplicity of layer-by-layer (LbL) assembly [1] – a method that involves the alternating adsorption from water of two or more polymers or other multivalent species with complementary interactions – has led to a recent and greatly accelerated growth of new drug delivery systems that take advantage of the mild aqueous conditions and high drug loadings that are possible using this method [2–4]. The ability to incorporate a broad range of therapeutic molecules at meaningful drug loadings, from small molecule drugs to sensitive biologics such as peptides, proteins, growth factors and nucleic acids has contributed significantly to this revolution. Furthermore, there is significant promise in the ability to release multiple drugs from a singular nanoscale thin film with independent release profiles of each drug tuned to the desired pharmacokinetics [5]. This promise is furthered by recent demonstrations that multilayer thin films can regulate not only relative release behavior, but yield time-sequenced release from surfaces [6,7]. Many exciting new applications involve the use of coated micron-sized particles and microcapsules that are of interest for localized release biomaterials, cellular mimics and the targeting of cells that readily engage with micronscale particles, such as macrophages and certain immunological cells [8]. The advantages described above are highly relevant to the goals of targeted nanomedicine, in which the nanoscale nature of the delivery vehicle itself enables accumulation of drug carriers in pathological tissues and access to tissues via various modes of cell penetration and entry. The concept of generating drug delivery nanoparticles that provide controlled, staged and/or triggered release of different drugs at appropriate points in the body is highly attractive to the treatment of cancer, infectious disease, lung, cardiovascular

Characterization of localized surface plasmon resonance transducers produced from Au25 nanoparticle multilayers

This article reports the preparation of gold plasmonic transducers using a nanoparticle self-assembly/heating method and the characterization of the films using scattering-type scanning near-field optical microscopy (s-SNOM). Nanoparticle-polymer multilayer films were prepared by the layer-by-layer assembly on glass slides by alternating exposures to monodisperse Au25 nanoparticles and ionic polymer linkers. Thermal evaporation of organic matters from the nanoparticle-polymer multilayer films at 600°C allowed the nanoparticles to coalescence and form nanostructured films. Characterization of the nanostructured films generated from Au25 nanoparticles using atomic force microscopy (AFM) showed that the films have rounded, small, island-like morphologies (d: 30–50nm) with a pit in the center of many islands. However, further characterizations with s-SNOM revealed that the produced nanoislands contain a single gold cluster in a pit surrounded by donut-shaped dielectric species. Formation of such a structure is thought to be resulted from the embedding of gold clusters under the reorganized polysiloxane binder coatings and glass surfaces during heat treatment of the Au25 nanoparticle multilayer films. The nanostructured films displayed strong surface plasmon resonance bands in UV–vis spectra with a peak absorbance occurring at ∼545–550nm. The optical sensing capability of the films was examined using d-glucose-functionalized gold island films with the interaction of Concanavalin A (ConA). The result showed that the adsorption of ConA on island films causes a large change in the LSPR band intensity.

Effects of temperature gradient induced nanoparticle motion on conduction and convection of fluid

The role of temperature gradient induced nanoparticle motion on conduction and convection was investigated. Possible mechanisms for variations resulting from variations in the thermophysical properties are theoretically and experimentally discussed. The effect of the nanoparticle motion on conduction is demonstrated through thermal conductivity measurement of deionized water with suspended CuO nanoparticles (50 nm in diameter) and correlated with the contributions of Brownian diffusion, thermophoresis, etc. The tendencies observed is that the magnitude of and the variation in the thermal conductivity increases with increasing volume fraction for a given temperature, which is due primarily to the Brownian diffusion of the nanoparticles. Using dimensional analysis, the thermal conductivity is correlated and both the interfacial thermal resistance and near-field radiation are found to be essentially negligible. A modification term that incorporates the contributions of Brownian motion and thermophoresis is proposed. The effect of nanoscale convection is illustrated through an experimental investigation that utilized fluorescent polystyrene nanoparticle tracers (200 nm in diameter) and multilayer nanoparticle image velocimetry. The results indicate that both the magnitude and the deviation of the fluid motion increased with increasing heat flux in the near-wall region. Meanwhile, the fluid motion tended to decrease with the off-wall distance for a given heating power. A corresponding numerical study of convection of pure deionized water shows that the velocity along the off-wall direction is several orders of magnitude lower than that of deionized water, which indicates that Brownian motion in the near-wall region is crucial for fluid with suspended nanoparticles in convection.

Direct release of synthetic antiferromagnetic nanoparticles fabricated by defect-free thermal imprinting

We report an improved process, using a defect-free thermal imprinting process that directly releases homogeneously patterned lithographic nanoparticles from a large-area wafer to water. Our method has a substantially larger yield and avoids all the pitfalls that are associated with the sacrificial layers in the traditional imprinting methods. By using an ethylene tetrafluoroethylene mold and a bi-layer resist lift-off, defect-free imprints were achieved in areas larger than 1 × 1 cm2. Illustrating the effectiveness of this method, high-quality planar Fe/Ta multi-layered magnetic nanoparticles, 300 nm in diameter, were deposited by ion-beam sputtering and their basic magnetic properties are characterized. These particles prepared by direct release with tunable magnetic properties and good engineering possibilities are ideal for a wide range of applications, including those specifically for biomedicine.

Carbon-supported ultra-high loading Pt nanoparticle catalyst by controlled overgrowth of Pt: Improvement of Pt utilization leads to enhanced direct methanol fuel cell performance

Carbon-supported Pt nanoparticle catalysts with ultra-high loading up to 85% are prepared by multi-step reduction (Pt/C-nR), in which additional Pt precursors are reduced upon a preformed Pt/C catalyst (Pt/C-1R). Transmission electron microscopy images show that the Pt/C-nR catalysts are composed of multilayers of Pt nanoparticles. The multiply stacked morphology in the Pt/C-nR catalysts may originate from the local overgrowth of additionally reduced Pt nanoparticles on the pre-existing Pt nanoparticles in the Pt/C-1R catalyst rather than conformal growth. The electrochemical characterizations by cyclic voltammograms in HClO4 solution reveal that Pt/C-2R catalyst exhibits an increased Pt utilization over the Pt/C-1R catalyst of the same Pt loading on the carbon support where a significant portion of catalytically active surfaces are buried within micropores of carbons. Furthermore, a direct methanol fuel cell (DMFC) single cell employing Pt/C-2R catalyst exhibits an enhanced DMFC performance compared to a single cell using the Pt/C-1R catalyst, demonstrating the importance of morphological control of Pt nanoparticles that can improve the catalyst utilization.

Self-assembled iron oxide nanoparticle multilayer: x-ray and polarized neutron reflectivity

We have investigated the structure and magnetism of self-assembled, 20 nm diameter iron oxide nanoparticles covered by an oleic acid shell for scrutinizing their structural and magnetic correlations. The nanoparticles were spin-coated on an Si substrate as a single monolayer and as a stack of 5 ML forming a multilayer. X-ray scattering (reflectivity and grazing incidence small-angle scattering) confirms high in-plane hexagonal correlation and a good layering property of the nanoparticles. Using polarized neutron reflectivity we have also determined the long range magnetic correlations parallel and perpendicular to the layers in addition to the structural ones. In a field of 5 kOe we determine a magnetization value of about 80% of the saturation value. At remanence the global magnetization is close to zero. However, polarized neutron reflectivity reveals the existence of regions in which magnetic moments of nanoparticles are well aligned, while losing order over longer distances. These findings confirm that in the nanoparticle assembly the magnetic dipole–dipole interaction is rather strong, dominating the collective magnetic properties at room temperature.

GISAXS analysis of 3D nanoparticle assemblies—effect of vertical nanoparticle ordering

We report on grazing-incidence small-angle x-ray scattering (GISAXS) study of 3D nanoparticle arrays prepared by two different methods from colloidal solutions—layer-by-layer Langmuir–Schaefer deposition and spontaneous self-assembling during the solvent evaporation. GISAXS results are evaluated within the distorted wave Born approximation (DWBA) considering the multiple scattering effects and employing a simplified multilayer model to reduce the computing time. In the model, particular layers are represented by nanoparticle chains where the positions of individual nanoparticles are generated following a model of cumulative disorder. The nanoparticle size dispersion is considered as well. Three model cases are distinguished—no shift between the neighboring chains (AA stacking), a shift equal to half of the mean interparticle distance (AB stacking) and random shift between the chains. The first two cases correspond to vertically correlated nanoparticle positions across different chains. A comparison of the experimental GISAXS patterns with the model cases enabled us to distinguish important differences between the 3D arrays prepared by the two methods. In particular, laterally ordered layers without vertical correlation of the nanoparticle positions were found in the nanoparticle multilayers prepared by the Langmuir–Schaefer method. On the other hand, the solvent evaporation under particular conditions produced highly ordered 3D nanoparticle assemblies where both laterally and vertically correlated nanoparticle positions were found.

Multi-Layer Pt Nanoparticle Embedded High Density Non-Volatile Memory Devices

This work presents high density non-volatile memory devices by embedding multi-layers of ∼1 nm Pt nanoparticles between Al2O3 tunneling, inter-particle, and blocking dielectric layers. Up to four layers of Pt nanoparticle embedded memory devices were fabricated using a unique Tilted Target sputter deposition method. A combination of angular deposition flux and self-limiting growth process resulted in the formation of nearly mono-dispersed metal nanoparticles at room temperature allowing the fabrication of multi-layer devices without the need for further annealing. Multi-layer Pt nanoparticle embedded memory devices showed an enhanced memory window dependent on the number of nanoparticle layers. The memory window of 14.68 V and an electron charge density of 2.6 × 1013 cm−2 were obtained at ±10 V sweeping gate voltage in quad-layer Pt nanoparticle embedded memory-a twofold increase when compared to the single-layer device. We also demonstrated that asymmetrical quad-layer Pt nanoparticle embedded memory reduced an initial charging and improved the charge retention property.