Multilayer Nanoparticles Research Articles

Optical Properties of Plasmon Resonances with Ag/SiO2/Ag Multi-Layer Composite Nanoparticles

Optical properties of plasmon resonance with Ag/SiO2/Ag multi-layer nanoparticles are studied by numerical simulation based on Green's function theory. The results show that compared with single-layer Ag nanoparticles, the multi-layer nanoparticles exhibit several distinctive optical properties, e.g. with increasing the numbers of the multi-layer nanoparticles, the scattering efficiency red shifts, and the intensity of scattering enhances accordingly. It is interesting to find out that slicing an Ag-layer into multi-layers leads to stronger scattering intensity and more “hot spots" or regions of stronger field enhancement. This property of plasmon resonance of surface Raman scattering has greatly broadened the application scope of Raman spectroscopy. The study of metal surface plasmon resonance characteristics is critical to the further understanding of surface enhanced Raman scattering as well as its applications.

Granular metals: From electronic correlations to strain-sensing applications

An analysis scheme is presented that allows for a quantitative description of the sensitivity of granular metal based strain sensors. The scheme draws on recent advances in the understanding of charge transport mechanisms in granular metals. How to deduct the relevant model parameters from temperature-dependent conductivity measurements is demonstrated by using recently published data for fcc-packed gold nanoparticle multilayers. Based on this model parameter set the intrinsic strain gauge factor is calculated as function of the intergrain coupling strength for different transport regimes. General trends for strain gauge factor optimization are identified. The absolute values for the calculated gauge factor are in good correspondence with typical values obtained for metal-containing diamondlike carbon thin film strain sensors.

Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy

Highly hydrophilic cotton fabrics were rendered superhydrophobic via electrostatic layer-by-layer assembly of polyelectrolyte/silica nanoparticle multilayers on cotton fibers, followed with a fluoroalkylsilane treatment. The surface morphology of the silica nanoparticle-coated fibers, which results in the variety of the hydrophobicity, can be tailored by controlling the multilayer number. Although with the static contact angle larger than 150°, in the case of 1 or 3 multilayers, the fabrics showed sticky property with a high contact angle hysteresis (>45°). For the cotton fabrics assembled with 5 multilayers or more, slippery superhydrophobicity with a contact angle hysteresis lower than 10° was achieved. The buoyancy of the superhydrophobic fabric was examined by using a miniature boat made with the fabric. The superhydrophobic fabric boat exhibited a remarkable loading capacity; for a boat with a volume of 8.0 cm 3, the maximum loading was 11.6 or 12.2 g when the boat weight is included. Moreover, the superhydrophobic cotton fabric showed a reasonable durability to withstand at least 30 machine washing cycles.

Combined Electrostatic-Covalent Building of Au NPs Multilayers and Their Size-Enhanced Cohesive and SERS Properties

Multilayers of well-ordered and close-packed 2D nanostructures of gold nanoparticles (NPs) were fabricated using a layer-by-layer technique. Colloidal spherical Au NPs of 5 and 15 nm diameters were synthesized and, respectively, self-assembled in multilayers. The robustness of these systems was insured by a combination of electrostatic and covalent bonds between nanoparticles and linker molecules. The compacity of the superlattice was characterized by AFM observation and ellipsometry measurements. Evidence of stronger cohesion of multilayers of smaller NPs size was brought by submitting the systems to sonication test. The multilayers have also proved analytical potential when used to detect low concentration methylene blue molecules adsorbed on the Au nanoparticles, by surface-enhanced Raman spectroscopy (SERS). The detection sensitivity of these two sized Au NPs architectures was directly compared to an evaporated “bulk” Au thin film of equivalent thickness. Results have displayed a strong increase of the electromagnetic field enhancement with a decrease of the NPs size, whereas the bulk thin Au film was shown to be inefficient as a SERS substrate. These results bring a nice evidence of size effects on the global performance (SERS, cohesion) and hopefully on the stability of NPs based nanostructures.

Possibility and necessity of constructing new nanoformula systems of traditional Chinese medicine

The past decade has witnessed the remarkable progress on nanotechnology and nanoherb. With the globally rapid development of nanotechnology, we are considering to construct new nanoformula systems of traditional Chinese medicine (TCM) by using porous materials, multilayered core-shell particles or nanoparticles containing various multifunctional parts. With the compatibility of sovereign, minister, assistant and courier in a formula, new nanoformula systems of TCM will have various advantages, such as containing multiple active species, controlled release, targeting function, and labeling and tracing capabilities. Using the latest breakthroughs of nanotechnology for the modern research of TCM will greatly help enhance the ability to investigate the principles of TCM, and to design, screen and utilize new nanoformula systems of TCM.

Multilayer nanoparticles with a magnetite core and a polycation inner shell as pH-responsive carriers for drug delivery

Nanocarriers with multilayer core-shell architecture were prepared by coating a superparamagnetic Fe(3)O(4) core with a triblock copolymer. The first block of the copolymer formed the biocompatible outermost shell of the nanocarrier. The second block that contains amino groups and hydrophobic moiety formed the inner shell. The third block bound tightly onto the Fe(3)O(4) core. Chlorambucil (an anticancer agent) and indomethacin (an anti-inflammation agent), each containing a carboxyl group and a hydrophobic moiety, were loaded into the amino-group-containing inner shell by a combination of ionic and hydrophobic interactions. The release rate of the loaded drugs was slow at pH 7.4, mimicking the blood environment, whereas the release rate increased significantly at acidic pH, mimicking the intracellular conditions in the endosome/lysosome. This can be attributed to the disruption of the ionic bond caused by protonation of the carboxylate anion of the drugs and the swelling of the inner shell caused by protonation of the amino groups.

Versatility and multifunctionality of highly reflecting Bragg mirrors based on nanoparticle multilayers

The use of both supported and flexible self-standing nanoparticle-based one dimensional photonic crystal films as effective frequency selective filters in the UV-vis-NIR is herein evaluated. The requirements to achieve a flat spectral response at the desired frequency range are analyzed and a synthetic route to realize materials with such properties presented. Strict control over the structural parameters yields multilayers in which the opening or closing of higher order photonic band gaps can be devised, thus leading to films capable of blocking the UV and NIR ranges simultaneously. Furthermore, the physico-chemical properties of the mirror can be modified to yield either moisture-repelling or, on the contrary, environmentally responsive optical filters. These materials present a great potential to be used as versatile and multifunctional optical elements.

Modified Langmuir-Blodgett deposition of nanoparticles - measurement of 2D to 3D ordered arrays

The ordered nanoparticle monolayers and multilayers over macroscopic areas were prepared by the modified Langmuir-Blodgett method. Using this approach, the nanoparticle monolayer is formed on the water surface by compression and subsequently it is transferred onto the substrate by a controlled removal of the water subphase. The ordering and homogeneity of the prepared mono- and multilayers was studied by scanning electron microscope (SEM), grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR) techniques. From the results it follows that an ordered nanoparticle monolayer was formed over a large area. For the multilayer, the layering and lateral ordering of each layer was confirmed by XRR and SEM performed after the deposition of each nanoparticle layer.

Layer-by-layer fabrication of well-packed gold nanoparticle assemblies guided by a β-sheet peptide network

In this study, we describe the first demonstration of well-ordered multilayer thin films of gold nanoparticles through a layer-by-layer (LbL) technique assisted by a polypeptide template. Anionic poly(L-glutamic acid) (PLGA)-modified gold nanoparticles were prepared as building units for LbL self-assembly. Two types of synthetic polymers, poly(L-lysine) (PLL) and poly(allylamine), were used as polycations that carry the same amino groups at the side chain, although the former is a polypeptide and the latter is a vinyl polymer. The deposition process and the resultant multilayer films were characterized by means of absorption, circular dichroism, Fourier transform infrared and atomic force microscopy measurements. Experimental results revealed that LbL multilayer properties, such as thickness, conformation of the peptide component, homogeneity and periodicity of nanoparticle layers, were significantly affected by the kind of polycations present. In particular, the combination of anionic PLGA-coated gold nanoparticles and cationic PLL induced β-sheet formation, which enabled the fabrication of a homogeneously well-packed gold nanoparticle multilayer without aggregation. LbL multilayer properties such as thickness, conformation of the peptide component, homogeneity and periodicity of nanoparticle layers were significantly affected by the kind of polycations. The combination of anionic PLGA-coated gold nanoparticle and cationic PLL induced a β-sheet formation, which enables the fabrication of a homogeneously well-packed gold nanoparticle multilayer without aggregation.

Electrical characterization of multilayered SiC nano-particles for application as tunnel barrier engineered non-volatile memory

SiC nano-particles on tunnel layer with variable oxide thickness composed of SiO 2 and Si 3N 4 layers were fabricated and their electrical properties were evaluated. The flat-band voltage shifts due to the memory effect of multilayered SiC nano-particles in the non-volatile memory (NVM) device with SiO 2/Si 3N 4/SiO 2, Si 3N 4/SiO 2/Si 3N 4 and SiO 2 tunnel layer were observed about 1.5, 1.4 and 0.2 V after the voltage sweep from −6 to 3 V under applied program/erase voltages at ±13 V for 10 ms, respectively. The program/erase speeds of ONO and NON tunnel layered devices were faster than that of the SiO 2 tunnel layer device. The memory window of the NVM devices with ONO tunnel layers after applied program/erase bias at ±10 V for 500 ms was maintained about 1.6 V after 10 5 s. These results indicate that the ONO and NON tunnel barriers can provide a thin effective tunneling thickness for the fast P/E speeds and comparatively thick physical thickness for the long charge retention characteristic.

On the formation mechanism of metal nanoparticle nanotubes

We have previously described nanoparticle nanotubes (NPNTs), i.e., tubular metallic nanostructures comprising coalesced nanoparticles (NPs), obtained by passing citrate-stabilized metal (Au, Ag, Pd) NP solutions through aminosilane-modified nanoporous alumina membranes. Here we show that the mechanism of NPNT formation involves two stages: (i) electrostatic binding of a monolayer of metal NPs to the amine groups on the membrane pore walls; and (ii) accumulation of NP multilayers and room-temperature coalescence to form solid nanotubes. Free-standing NPNTs are obtained by post-dissolution of the membrane template. An improved fabrication apparatus enabled evaluation of the role of drying and other preparation parameters on the NP coalescence and NPNT formation and structure. Intermittent drying during the NP accumulation stage is necessary for the formation of solid NPNTs, while a slow flow rate of the colloid solution through the membrane pores and reversal of the flow direction promote the formation of more uniform and longer NPNTs.

Abstract C66: A novel technique to quantify condensation/decondensation status in the nuclear subdomains by QD-FRET

Abstract Recent studies have reported that control of nuclear decondensation at specific nuclear subdomains (i.e. euchromatin) is highly desired for the efficient transfection efficiency. Here, we have established a novel technology for the imaging of nuclear condensation/decondensation status in the nuclear subdomains (i.e. heterochromatin and euchromatin) by based on the three key technologies. One is imaging of fluorescence resonance energy transfer (FRET) between quantum dots (QDs)-labeled plasmid DNA (pDNA) as a donor, and acceptor-labeled polycation, which can monitor a specific molecular interactions at the nanometre scale. The second technology is a multilayered lipid envelope-type nanoparticle, which we refer to as a Tetra-lamellar Multi-functional Envelope-type Nano Device (T-MEND). The critical structural elements of the T-MEND are a DNA—polycation condensed core coated with two nuclear membrane-fusogenic inner envelopes and two endosome-fusogenic outer envelopes, which are designed for nuclear delivery via a stepwise fusion. It is required to evaluate the nuclear dispositions in relation to the transgene expression, to avoid a situation that intracellular trafficking processes rate-limit transfection activity. The last one is confocal image-assisted 3-dimensionally integrated quantification (CIDIQ) method. In this method, fluorophore-labeled pDNA was transfected in HeLa cell line, and then intracellular distribution was distinguished by staining organelle. Z-series of confocal images were captured by confocal laser scanning microscopy (CLSM), and thereafter, pDNA was quantified based on the pixel area of the signals derived from the fluorophore on pDNA in nuclear subdomains (heterochromatin and euchromatin). As a model of the analysis, QD-labeled DNA was condensed with reductive environment-dependently cleavable polyrotaxane (DMAE-ss-PRX), an artificial condenser, and encapsulated in T-MEND. As a result, transfection activity depends on the number of cationic DMAE of cyclodextrin (α-CD), in conjunction with a drastic change in decondensation efficiency in euchromatin region. These data collectively indicate that this imaging technology is highly advantageous to clarify the dynamics of plasmid DNA in post-nuclear delivery process of cancer cells. Citation Information: Cancer Res 2009;69(23 Suppl):C66.

Effective catalytic electrode system based on polyviologen and Au nanoparticles multilayer

Au nanoparticles encapsulated by very labile chloride ions are synthesised and characterised. Through layer-by-layer deposition technique they are stably anchored to an electrode surface, using a polyviologen derivative as the polycationic organic component. The structure and morphology of the multilayer is exhaustively studied by UV–vis spectroscopy, X-ray diffraction, scanning and transmission electron microscopy. The nanocomposite material shows very interesting electrocatalytic properties with respect to the reduction of H 2O 2, which occurs at particularly less negative potentials. Furthermore, the presence of Au nanoparticles inside the electrode coating greatly improves the sensitivity of the electrochemical system. The system results to be a well suitable sensor for H 2O 2 quantification, with high sensitivity and low detection limit.

Self-assembled multilayers of polyethylenimine, DNA and gold nanoparticles. A study of electron transfer reaction

The present manuscript describes studies of the electron transfer kinetics at gold electrodes modified by electrostatic self-assemblies of polyethylenimine (PEI), DNA and gold nanoparticles (NP) by Scanning Electrochemical Microscopy (SECM). Two redox mediators of similar structure, ferrocenemethanol (FcOH), and ferrocenecarboxylic acid (FcCOOH) were used to evaluate the effect of the electrode modification on the electron transfer process. For both redox probes, the observed electrochemical behavior was dependent of the charge of the external layer of the self-assembled structure. The corresponding apparent heterogeneous rate constant, k0, was determined. The effect of NP adsorption was also evaluated. Independently of the mediator used, an increase of the k0 was observed when NPs were incorporated, and the surfaces presented a conductive behavior similar to the bare gold electrode. SECM images using FcOH as redox mediator were also recorded. Variations in the normalized currents permitted to evaluate differences of the surface electroactivity due to the polymers and/or nanoparticles adsorption.

Nanoscale Architecture Dictates Detection Profile of Surface-Confined DNA by MALDI-TOF MS

The design and fabrication of various nanoscale architectures for the effective MALDI-TOF MS analysis of surface-confined DNA are reported. The nanoscale architectures are derived from layer-by-layer assemblies of negatively charged nanoparticles and positively charged polymers. An important finding is that porous structures comprising bottom SiO(2) nanoparticle layers and top Au nanoparticle layers enable the observation of both covalently bound (with Au-S bond) and hybridized oligonucleotides. The achievement of this unprecedented detection capability is attributed to the unique combination of a nanoporous dielectric film and discrete noble metal nanoparticles. The conclusion is supported by control experiments performed on a variety of single and multilayered Au nanoparticle structures, where only the hybridized oligonucleotides in a two- or three-strand system could be detected.

Multilayered Magnetic Nanoparticles as a Support in Solid-Phase Peptide Synthesis

The synthesis of multilayered magnetic nanoparticles (MNPs) for use as a support in solid-phase peptide synthesis (SPPS) is described. Silanization of magnetite (Fe3O4) nanoparticles with 3-(trimethoxysilyl)propyl methacrylate introduced polymerizable groups on the surface. Polymerization with allylamine, trimethylolpropane trimethacrylate, and trimethylolpropane ethoxylate (14/3 EO/OH) triacrylate provided a polymeric coating and amino groups to serve as starting points for the synthesis. After coupling of an internal reference amino acid and a cleavable linker, the coated MNPs were applied as the solid phase during synthesis of Leu-enkephalinamide and acyl carrier protein (65-74) by Fmoc chemistry. A “high-load” version of the MNP support (0.32 mmol/g) was prepared by four consecutive cycles of Fmoc-Lys(Fmoc)-OH coupling and Fmoc deprotection. Successful synthesis of Leu-enkephalin was demonstrated on the “high-load” MNPs. Chemical stability studies proved the particles to be stable under SPPS conditions and magnetization measurements showed that the magnetic properties of the particles were maintained throughout derivatizations and SPPS. The MNPs were further characterized by high-resolution transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, elemental analysis, and nitrogen gas adsorption measurements.

Fabrication of Fe Nanoparticle Assemblies on Au(111) with Xe Buffer Layer and Low Temperature Growth

Growth of Fe nanoparticle assemblies on Au(111) herringbone surface is systematically studied by scanning tunneling microscope (STM) through the variation of (1) deposition coverage, (2) substrate temperature, (3) Xe buffer layer assisted growth (BLAG), and (4) nucleation seed effect. 0.09–0.18 ML Fe deposited at 230–250 K results in regular nanoparticle arrays, which can serve as templates with well-ordered nucleation sites for subsequent growth. BLAG and 90 K growth lead to the multi-layer height nanoparticles. Combination of Xe buffer layer and nucleation seeds is demonstrated to be a new method for the nanoparticle growth on nano-patterned template, maintaining the three-dimensional shape and ordering without lateral percolation.

FRET Enhancement in Multilayer Core−Shell Nanoparticles

This study describes the preparation and characterization of novel multilayer core-shell nanoparticles displaying metal-enhanced Forster resonant energy transfer. The increase in range and efficiency of Forster resonant energy transfer in these fluorescent nanocomposites and their vastly improved luminosity make them promising optical probes for a variety of applications such as cell imaging and biosensing.

Efficient Electro-Oxidation of Water near Its Reversible Potential by a Mesoporous IrOx Nanoparticle Film

We describe the formation of stable, adherent, mesoporous films of 2 nm diameter IrIVOx nanoparticles on glassy carbon electrodes, by a previously unreported method of controlled potential electro-flocculation from pH 13 nanoparticle solutions. These films initiate O2 evolution from water oxidation and then achieve 100% current efficiency, at overpotentials only ∼0.15 and ∼0.25 V higher, respectively, than the reversible H2O/O2 potential. The overpotentials, measured at ∼0.5 mA/cm2, are independent of pH and are the smallest yet reported for electrochemical water oxidation, a property important in possible uses in electrochemical solar cells. The films appear to be mesoporous and microscopically accessible, since O2 evolution currents increase proportionately to multilayer nanoparticle film coverage but without a concurrent increase in overpotential.

Heme Protein Assisted Dispersion of Gold Nanoparticle Multilayers on Chips: From Stabilization to High-Density Double-Stranded DNAs Fabricated in Situ for Protein/DNA Binding

Heme proteins in general are shown to be an effective linking agent in stabilizing gold nanoparticles (AuNPs) and thus facilitate the fabrication of three-dimensional (3D) AuNP multilayers on a chip, resulting in a higher coating density than that on polymer linker anchored surfaces for analytical applications. With the use of electron spectroscopy for chemical analysis (ESCA) measurements, a lower oxidation state of Au(0) and dramatic changes among multiple chemical states of N1s are detected upon coating AuNPs with heme proteins but not detected upon coating AuNPs with non-heme proteins. Thus, we propose that the stabilization power arises from pi-conjugation between AuNPs and the heme group. We also propose that such conjugation must be facilitated by the exposure of the heme group through a conformational change of the protein as well as interactions of other functional groups with AuNPs to bring the heme moiety to a close face-to-face distance with the AuNPs. A high-density double-stranded DNA (dsDNA) composed of a sequence of estrogen response element (ERE) is then fabricated on heme protein anchored chips. An in situ hybridization and tracking method is developed based on hybridization-induced fluorescence restoration associated with AuNPs and assists in the subsequent detection of DNA/protein binding on the same chip. The AuNP ERE chips are shown to have high sensitivity and specificity for quantitative detection of ERE binding with its two transcription factor isoforms, estrogen receptors alpha and beta (ERalpha and ERbeta), in cell lysates with reduced reagents and reaction time.