Multilayer Nanoparticles Research Articles

Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C1C2Im][OTf] Monitored by In Situ IR Spectroscopy.

The synthesis of ionic-liquid-modified nanomaterials has attracted much attention recently. In this study we explore the potential to prepare such systems in an ultraclean fashion by physical vapor codeposition (PVCD). We codeposit metallic cobalt and the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C1C2Im][OTf] simultaneously onto a Pd(111) surface at 100 K. This process is performed under ultrahigh-vacuum (UHV) conditions in the presence of CO, or in the presence of O2 and CO. We use time-resolved (TR) and temperature-programmed (TP) infrared reflection absorption spectroscopy (IRAS) to investigate the formation and stability of the IL-modified Co deposits in situ during the PVD-based synthesis. CO is used as a probe molecule to monitor the growth. After initial growth of flat Co films on Pd(111), multilayers of Co nanoparticles (NPs) are formed. Characteristic shifts and intensity changes are observed in the vibrational bands of both CO and the IL, which originate from the electric field at the IL/Co interface (Stark effect) and from specific adsorption of the [OTf](-) anion. These observations indicate that the Co aggregates are stabilized by mixed adsorbate shells consisting of CO and [OTf](-). The CO coverage on the Co particle decreases with increasing temperature, but some CO is preserved up to the desorption temperature of the IL (370 K). Further, the IL shell suppresses the oxidation of the Co NPs if oxygen is introduced in the PVCD process. Only chemisorbed oxygen is formed at oxygen partial pressures that swiftly lead to formation of Co3O4 in the absence of the IL (5 × 10(-6) mbar O2). This chemisorbed oxygen is found to destabilize the CO ligand shell. The oxidation of Co is not suppressed if IL and Co are deposited sequentially under otherwise identical conditions. In this case we observe the formation of fully oxidized cobalt oxide particles.

Colorimetric Detection of an Airborne Remote Photocatalytic Reaction Using a Stratified Ag Nanoparticle Sheet.

Photocatalysts are practically used for decomposition of harmful and fouling organic compounds. Among the photocatalytic reactions, remote oxidation via airborne species is a relatively slow process, so that a sensitive technique for its detection has been awaiting. Here, we investigated an airborne remote photocatalytic reaction of a TiO2 photocatalyst modified with Pt nanoparticles as co-catalysts via the color change caused by a decomposition of a multilayered silver nanoparticle sheet. The silver nanoparticle sheet fabricated by the Langmuir-Schaefer method on a gold substrate exhibits a unique multicolor depending upon the number of layers. The color originates from multiple light trapping in the stratified sheets that has a metamaterial characteristic along with an intra- and interlayer coupling of localized surface plasmon resonance (LSPR). The stepwise decomposition of the sheets was confirmed by the colorimetric data, which exhibited not only a monotonic decrease but also a maximized absorption of light when the film thickness reached the optimal thickness for light trapping or when the oxidation of the Ag core started. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance (SPR) spectroscopy data provided a complete view of the decomposition process of this inorganic-organic nanocomposite film, and simulation by the transfer-matrix method explained a simultaneous plasmonic response rationally. The influence of the humidity and gas flow rate on the airborne remote photocatalytic reaction kinetics was examined by this colorimetric detection method, and it suggests that H2O in air plays an essential role in the reaction.

The multilayer nanoparticles for deep penetration of docetaxel into tumor parenchyma to overcome tumor microenvironment

Deep penetration of the anticancer drug, docetaxel (DTX), into tumor parenchyma was demonstrated to achieve improved chemotherapy. For this purpose, a multistage nanostructure was designed and characterized using the multilayer nanoparticles (NPs). The multilayer NPs had a core/shell structure. The core was composed of the DTX-loaded Pluronic NPs (diameter: 12nm) that were transferred into the inner side of vesicles to form the vesicle NPs. Förster resonance energy transfer (FRET) in the NPs was observed to verify the incorporation of the DTX-loaded Pluronic NPs into the inner side of the vesicles during the formation of the vesicle NPs. Subsequently, the vesicle NPs were stabilized through Pluronic-lipid bilayer interaction to form the multilayer NPs. To examine the morphology and size distribution of the multilayer NPs, transmittance electron microscopy and dynamic light scattering were used. In vitro release behavior and toxicity were observed to verify the functionality of the multilayer NPs as nanocarriers for cancer therapy. Multistage functionality was evaluated by cellular uptake and tissue distribution behaviors of the multilayer NPs. The biodistribution of the multilayer NPs and their antitumor efficacy were also observed to understand the role of multistage functionality for improved chemotherapy.

Three-dimensional particle tracking around microstructures in water via total internal reflection fluorescence microscopy and refractive-index-matching method

Multilayer nanoparticle image velocimetry (MnPIV) with a refractive-index-matching method is powerful technique for x–y–z (3D) flow measurement, because it can detect the 3D position of fluorescent particles with submicron resolution. In MnPIV, the intensity of fluorescence of a particle is used to estimate its z-position. However, it has been difficult to measure 3D flows around microstructures in water by total internal reflection fluorescence microscopy because of light scattering caused by the different refractive indices of the structures and the working fluid. By using a thermal nanoimprinting technique, we succeeded in fabricating microstructures from a polymer resin whose refractive index is equal to that of water, and we used these microstructures to perform MnPIV in water. As a result of the match between the refractive index of water and that of the microstructures, we were able to perform 3D tracking of nanoparticles around the microstructures in water.

Nanoparticles for Targeting Intratumoral Hypoxia: Exploiting a Potential Weakness of Glioblastoma.

Extensive hypoxic regions are the daunting hallmark of glioblastoma, as they host aggressive stem-like cells, hinder drug delivery and shield cancer cells from the effects of radiotherapy. Nanotechnology could address most of these issues, as it employs nanoparticles (NPs) carrying drugs that selectively accumulate and achieve controlled drug release in tumor tissues. Methods overcoming the stiff interstitium and scarce vascularity within hypoxic zones include the incorporation of collagenases to degrade the collagen-rich tumor extracellular matrix, the use of multistage systems that progressively reduce NP size or of NP-loaded cells that display inherent hypoxia-targeting abilities. The unfavorable hypoxia-induced low pH could be converted into a therapeutical advantage by pH-responsive NPs or multilayer NPs, while overexpressed markers of hypoxic cells could be specifically targeted for an enhanced preferential drug delivery. Finally, promising new gene therapeutics could also be incorporated into nanovehicles, which could lead to silencing of hypoxia-specific genes that are overexpressed in cancer cells. In this review, we highlight NPs which have shown promising results in targeting cancer hypoxia and we discuss their applicability in glioblastoma, as well as possible limitations. Novel research directions in this field are also considered.

Novel pH-responsive multilayer magnetic nanoparticles for controlled drug delivery

A multifunctional nanocarrier with multilayer core–shell architecture was prepared by chemical modification of Fe3O4 magnetic nanoparticle (MNPs) with acrolein–styrene–polyethyleneimine (AL–St–PEI) via covalent bonding. MNPs were prepared by co-precipitation method, and then, thiol functionalized (MNPs-SH) were synthesized by treating MNPs with the (3-mercaptopropyl) trimethoxysilane. Subsequently, the copolymerization of St and AL was performed in the presence of the MNPs-SH and butyrolactam by thiol-lactam initiated radical polymerization. Finally, PEI was covalently bounded to the aldehyde groups on the surface of AL–St copolymer. The AL–St–PEI MNPs were investigated by FTIR, XRD, TGA, SEM and TEM. The drug release from AL–St–PEI MNPs was evaluated using doxorubicin as the model anticancer. Furthermore, to determine the effect of drug structure in the release profile from the modified MNPs, some lipophilic model drugs were studied in loading and release study. It was found that the nature of the drugs affect the release profile. The in vitro release modeling demonstrated that doxorubicin release is described by zero-order mechanism while release of lipophilic model drugs is controlled by fickian diffusion.

Highly Emissive Nd3+‐Sensitized Multilayered Upconversion Nanoparticles for Efficient 795 nm Operated Photodynamic Therapy

Photodynamic therapy (PDT) is a noninvasive and site‐specific therapeutic technique for the clinical treatment of various of superficial diseases. In order to tuning the operation wavelength and improve the tissue penetration of PDT, rare‐earth doped upconversion nanoparticles (UCNPs) with strong anti‐stokes emission are introduced in PDT recently. However, the conventional Yb3+‐sensitized UCNPs are excited at 980 nm which is overlapped with the absorption of water, thus resulting in strong overheating effect. Herein, a convenient but effective design to obtain highly emissive 795 nm excited Nd3+‐sensitized UCNPs (NaYF4:Yb,Er@NaYF4:Yb0.1Nd0.4@NaYF4) is reported, which provides about six times enhanced upconversion luminescence, comparing with traditional UCNPs (NaYF4:Yb,Er@NaYF4). A colloidal stable and non‐leaking PDT nanoplatform is fabricated later through a highly PEGylated mesoporous silica layer with covalently linked photosensitizer (Rose Bengal derivative). With as‐prepared Nd3+‐sensitized UCNPs, the nanoplatform can produce singlet oxygen more effective than traditional UCNPs. Significant higher penetration depth and lower overheating are demonstrated as well. All these features make as‐prepared nanocomposites excellent platform for PDT treatment. In addition, the nanoplatform with uniform size, high surface area, and excellent colloidal stability can be extended for other biomedical applications, such as imaging probes, biosensors, and drug delivery vehicles.

Biotin-Conjugated Multilayer Poly [D,L-lactide-co-glycolide]-Lecithin-Polyethylene Glycol Nanoparticles for Targeted Delivery of Doxorubicin

Multilayer nanoparticle combining the merits of liposome and polymer nanoparticle has been designed for the targeted delivery of doxorubicin (DOX) in cancer treatment. In this study, DOX-PLGA-lecithin-PEG-biotin nanoparticles (DOX-PLPB-NPs) were fabricated and functionalized with biotin for specific tumor targeting. Under the transmission electron microscopy observation, the lipid layer was found to be coated on the polymer core. The physical characteristics of PLPB-NPs were also evaluated. The confocal laser scanning microscopy confirmed the cellular uptake of nanoparticles and targeted delivery PLPB-NPs. The in vitro release experiment demonstrated a pH-depending release of DOX from drug-loaded PLPB-NPs. Cytotoxicity studies in HepG2 cells and in vivo antitumor experiment in tumor-bearing mice both proved DOX-PLPB-NPs showed the best inhibition effect of tumor proliferation. In biodistribution studies, DOX-PLPB-NPs showed a higher DOX concentration than free DOX and DOX-PLGA-lecithin-PEG nanoparticles (DOX-PLP-NPs) in tumor site, especially in 24 h, and the lowest DOX level in normal organs. The results were coincident with the strongest antitumor ability showed among in vivo antitumor experiment. Histopathology analysis demonstrated that DOX-PLPB-NPs exhibited the strongest antitumor ability and lowest cardiotoxicity. In brief, the PLPB-NPs were proved to be an efficient delivery system for tumor-targeting treatment.

Regulating Cell Apoptosis on Layer-by-Layer Assembled Multilayers of Photosensitizer-Coupled Polypeptides and Gold Nanoparticles.

The design of advanced, nanostructured materials by layer-by-layer (LbL) assembly at the molecular level is of great interest because of the broad application of these materials in the biomedical field especially in regulating cell growth, adhesion, movement, differentiation and detachment. Here, we fabricated functional hybrid multilayer films by LbL assembly of biocompatible photosensitizer-coupled polypeptides and collagen-capped gold nanoparticles. The resulting multilayer film can well accommodate cells for adhesion, growth and proliferation. Most significantly, controlled cell apoptosis (detachment) and patterning of the multilayer film is achieved by a photochemical process yielding reactive oxygen species (ROS). Moreover, the site and shape of apoptotic cells can be controlled easily by adjusting the location and shape of the laser beam. The LbL assembled multilayer film with integration of functions provides an efficient platform for regulating cell growth and apoptosis (detachment).

Structure and magnetic properties of multi-layered ZrO2 nanoparticles embedded in Al2O3 matrix and doped with 57Fe3+ ions

The multi-layered 3–8 nm ZrO2 particles doped with 57Fe3+ ions were synthesized by successive impregnations of Al2O3 with a solution of Zr isopropoxide and 57Fe acetylacetonate. This gave (FeZrO2)/Al2O3 samples containing ZrO2 (≈30 mass%) and different Fe content (0.06–0.26 mass%). By means of XRD, TEM and EDS techniques, it was found that the size of ZrO2 nanoparticles in the (FeZrO2)/Al2O3 samples increases in proportion to the Fe content. According to magnetic measurements and Mössbauer spectroscopy data, (FeZrO2)/Al2O3 samples contain two types of paramagnetic high-spin 57Fe3+ ions. The 57Fe3+ ions of type (I) are most probably adsorbed on the outer surface of ZrO2 nanoparticles and are responsible for the spin-lattice relaxation observed in the (FeZrO2)/Al2O3 samples. The 57Fe3+ ions of type (II) are embedded in the bulk of ZrO2 nanoparticles by replacing the octahedral Zr4+ positions to give a mixed oxide. As the Fe content in the (FeZrO2)/Al2O3 samples increases, the fraction 57Fe3+ ions of type (I) decreases, while that of 57Fe3+ ions of type (II) increases.

Self‐Assembled Multilayer‐Stabilized Nickel Nanoparticle Catalyst for Ligand‐Free Cross‐Coupling Reactions: in situ Metal Nanoparticle and Nanospace Simultaneous Organization

AbstractWe have developed a conceptually and methodologically novel self‐assembled multilayer nickel nanoparticle (NP) catalyst – sulfur‐modified gold‐supported Ni NPs (SANi) – for organic synthesis. The SANi catalyst was easily prepared through a three‐step procedure involving simultaneous in situ metal NP and nanospace organization. This unique method does not require any conventional preformed template for immobilizing and stabilizing NPs. SANi catalyzes carbon‐carbon bond‐forming cross‐coupling, Kumada coupling, and Negishi coupling reactions under ligand‐free conditions and can be used repeatedly for these reactions. Physical analysis of SANi showed that the active species in these reactions are self‐assembled multilayer zerovalent Ni NPs with a size of ∼3 nm.magnified image

Layer-by-layer Deposition of TiO2 Nanoparticles in the Wood Surface and its Superhydrophobic Performance

A hydrophilic wood surface was transformed to become superhydrophobic by layer-by-layer (LbL) assembly of polyelectrolyte/titanium dioxide (TiO2) nanoparticles multilayers and subsequent hydrophobic modification with 1H, 1H, 2H, 2H-perfluoroalkyltriethoxysilane (POTS). The chemical composition of the wood samples before and after treatment was characterized by energy dispersive X-ray analysis (EDXA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). These analyses showed that a high-surface-roughness film of TiO2 nanoparticles deposited by LbL became combined on the wood surface with a low-surface-energy thin layer of POTS. The microstructure and the hydrophobicity of the wood samples were analyzed by scanning electron microscope (SEM) and contact angle measurements, respectively. The morphology and the values of water contact angle (WCA) demonstrated that the reaction pH and number of self-assembled layers were the main factors affecting hydrophobic wood samples. After assembly with 5 or more multilayers, the wood surface exhibited excellent superhydrophobicity with the highest WCA of 161°.

Docetaxel-loaded multilayer nanoparticles with nanodroplets for cancer therapy.

A mixture of docetaxel (DTX) and Solutol® HS 15 (Solutol) transiently formed nanodroplets when it was suspended in an aqueous medium. However, nanodroplets that comprised DTX and Solutol showed a rapid precipitation of DTX because of their unstable characteristics in the aqueous medium. The incorporation of nanodroplets that comprised DTX and Solutol through vesicle fusion and subsequent stabilization was designed to prepare multilayer nanoparticles (NPs) with a DTX-loaded Solutol nanodroplet (as template NPs) core for an efficient delivery of DTX as a chemotherapeutic drug. As a result, the DTX-loaded Solutol nanodroplets (~11.7 nm) were observed to have an increased average diameter (from 11.7 nm to 156.1 nm) and a good stability of the hydrated NPs without precipitation of DTX by vesicle fusion and multilayered structure, respectively. Also, a long circulation of the multilayer NPs was observed, and this was due to the presence of Pluronic F-68 on the surface of the multilayer NPs. This led to an improved antitumor efficacy based on the enhanced permeation and retention effect. Therefore, this study indicated that the multilayer NPs have a considerable potential as a drug delivery system with an enhanced therapeutic efficacy by blood circulation and with low side effects.

Amperometric Glucose Biosensor Based on Effective Self-Assembly Technology for Preparation of Poly(allylamine hydrochloride)/Au Nanoparticles Multilayers.

Novel nanomaterials and nanotechnology for use in bioassay applications represent a rapidly advancing field. This study developed a novel method to fabricate the glucose biosensor with good gold nanoparticles (AuNPs) fixed efficiency based on effective self-assembly technology for preparation of multilayers composed of poly(allylamine hydrochloride) (PAH) and AuNPs. The electrochemical properties of the biosensor based on (AuNPs/PAH)n/AuNPs/glucose oxide (GOD) with different multilayers were systematically investigated. Among the resulting glucose biosensors, electrochemical properties of the biosensor with three times self-assembly processes ((AuNPs/PAH)3/AuNPs/GOD) is best. The GOD biosensor exhibited a fast amperometric response (5 s) to glucose, a good linear current-time relation over a wide range of glucose concentrations from 0.05 to 162 mM, and a low detection limit of 0.029 mM. The GOD biosensor modified with (AuNPs/PAH)n layers will have essential significance and practical application in future owing to the simple method of fabrication and good performance.

Materials and applications of flexible metamaterials and plasmonics

Given the ability to bend, stretch and roll like stretchable electronics, the newly developed metamaterial and plasmonic devices would open new chapters in functional optics. They can manipulate the electromagnetic waves in unprecedented forms and realize powerful applications like invisibility cloaking, sub-wavelength imaging, transformation optics and functional sensors etc. This review focused on the recent development in soft, flexible metamaterials and plasmonics that resonate from microwave to visible frequencies, various applications have been realized in filters, sensors and surface enhanced Raman spectroscopy etc. Optical structure designs are ranged from split ring resonators, multilayer fishnet metamaterials and nanoparticle arrays. Common soft substrates include polyimide, polydimethysiloxane, polyethylene terephthalate and polyethylene naphthalene. Their mechanical and optical properties were discussed. Compatible fabrication techniques such as conventional photolithography, electron beam lithography and a few newly developed nanofabrication techniques were introduced. Among which, nanoimprint and nanotransfer techniques that result in large area, low cost, high quality soft metamaterials and plasmonics are promising in wearable and tunable applications.

Functionalization of multilayer carbon shell-encapsulated gold nanoparticles for surface-enhanced Raman scattering sensing and DNA immobilization

In this paper, we reported the surface modification of multilayer carbon shell-encapsulated gold nanoparticles (Carbon Nanoparticles, or CNPs) via an oxygen plasma treatment approach and their subsequent functionalization with extraneous gold (Au) nanoparticles for Surface-enhanced Raman Scattering (SERS) sensing and DNA immobilization. The oxygen plasma treatment process led to purification of the multilayer carbon shell, reduction of the shell thickness, and derivatization of carbon shell with functional carboxylic groups. This further opens potential opportunities for surface functionalization of CNPs with extraneous Au nanoparticles or λ-DNA fragments, which were both achieved through a well-defined carbodiimide based covalent linking chemistry without removing the CNPs from the substrate. The resulting CNP–Au nanoparticle hybrids as well as the CNP-DNA architectures were characterized using various microscopic and spectroscopic techniques. The CNP–Au nanoparticle hybrids were further used as highly-sensitive SERS substrate for the detection of trace amount water-containing organic molecule. Meanwhile, they were also fundamentally simulated for their plasmonic behavior using discrete dipole approximation (DDA) method to understand the basic Raman enhancement principle. On the other hand, highly-ordered assembly of CNP-DNA architectures were also demonstrated in detail for their great potential in future DNA detection/recognition and bio-device applications.

Исследование рассеивающих свойств многослойных сферических наночастиц

Исследование рассеивающих свойств многослойных сферических наночастиц

Polymeric nanoparticle systems for non-viral gene delivery

Event Abstract Back to Event Polymeric nanoparticle systems for non-viral gene delivery Corey J. Bishop1*, Stephany Y. Tzeng1*, Kristen L. Kozielski1*, Alfredo Quinones-Hinojosa2, 3* and Jordan Green1, 2, 3 1 Johns Hopkins University School of Medicine, Biomedical Engineering, United States 2 Johns Hopkins University School of Medicine, Neurosurgery, United States 3 Johns Hopkins University School of Medicine, Oncology, United States Introduction: Through engineering polymer and nanoparticle properties, non-viral intracellular delivery of DNA and siRNA can be made efficacious. By delivering DNA in conjunction with inorganic nanoparticles, such as biocompatible gold nanoparticles, therapeutic function (gene/thermotherapy) can be combined with diagnostic function (imaging). Figure 1. Representative PBAE polymer 447 Materials and Methods: Libraries of poly(beta-amino esters) (PBAEs) were synthesized as described[1]. As an example, to synthesize polymer 447 (Figure 1), 1,4-butanediol diacrylate and 4-amino-1-butanol were reacted neat in a 1.2:1 molar ratio for 24 hrs. Subsequently, the linear polymers were end-capped with 1-(3-aminopropyl)-4-methylpiperazine in anhydrous tetrahydrofuran (THF) for 1 hour at 1000 RPM. Polymeric nanoparticles were formed by combining cationic PBAEs with anionic DNA or siRNA and allowing for self-assembly. Gold nanoparticles (AuNPs) were synthesized via a modified Frens method. Multilayer theranostic nanoparticles were designed following Figure 2. Fluorescence microscopy and flow cytometry were performed over time to measure transfection efficacy of reporter genes in GB319 human glioblastoma cells. siRNA-mediated gene knockdown was performed in constitutively eGFP positive GB319s. Cellular viability was measured by the CellTiter96® assay. In vivo evaluation of non-viral gene delivery nanoparticles was performed in an orthotopic patient-derived glioblastoma model in male nude athymic mice[2]. Figure 2. The layer-by-layer (LbL) fabrication process to create inorganic/polymeric hybrid nanoparticles. Results and Discussion: Non-bioreducible PBAE nanoparticles were found to be highly effective for DNA delivery, reaching 90% transfection efficacy without causing non-specific cytotoxicity. Certain bioreducible PBAE nanoparticles were found to be relatively ineffective for DNA delivery, but highly effective for siRNA delivery. These bioreducible nanoparticles led to 90% gene knockdown also without causing non-specific cytotoxicity. Polymers with increased hydrophobicity were found to be more effective for both DNA and siRNA delivery. When administered in vivo, 447/DNA nanoparticles successfully transfected the patient-derived glioblastoma cells in the mouse model and also demonstrated tumor-cell specific transfection. To enable kinetic control of exogenous gene expression of multiple genes, layer-by-layer (LbL) inorganic/polymeric hybrid nanoparticles were successfully fabricated. The zeta potential of the LbL inorganic/polymeric nanoparticles reversed at each of the 7 stages of layering, confirming that the coatings of each polyelectrolyte layer were achieved. The outer eGFP DNA layer of the LbL inorganic/polymeric nanoparticles transfected highly at day 2 and this level of gene expression persisted until day 9, when it then decreased over time (Figure 3). In contrast, the inner dsRed DNA layer had low expression initially that steadily increased to a maximum at day 9. Temporal control of multi-gene delivery was achieved by the physical placement of these different plasmids within the LbL layers and by biomaterial properties. Figure 3. Normalized transfection efficacies of inorganic/polymeric hybrid nanoparticles demonstrating temporal control of exogenous gene expression in human glioblastoma cells. Conclusion: Using a polymer library approach we were able to achieve high non-viral DNA delivery with low cytotoxicity as well as high siRNA knockdown with low cytotoxicity to human brain cancer cells. Certain polymer features, including hydrophobicity and mode of degradation, were key parameters for the effective nanomaterials. In addition, these nanoparticles showed efficacy in vivo in a human glioblastoma mouse model. Using an LbL approach, we were able to successfully develop a method to electrostatically coat inorganic theranostic nanoparticles that can load two different types of plasmids and deliver them with temporal control. National Institutes of Health (R01EB016721)

Highly effective and uniform SERS substrates fabricated by etching multi-layered gold nanoparticle arrays.

Gold nanoparticle multilayers printed on silicon substrates layer by layer were etched by a gold etchant to form highly effective and uniform substrates for surface-enhanced Raman scattering (SERS). The performance of the SERS substrates was systematically studied by adjusting the number of nanoparticle layers and the etching time. The optimized enhancement factor (EF) and the detection limit of the substrates were determined to be 8.6 × 10(6) and 1 × 10(-12) M, respectively. The high EF and low detection limit were attributed to the high density of "hot-spots" and the facile accession of probe molecules to these spots. Moreover, the SERS substrates exhibited a nice uniformity with a small spot-to-spot variation and a good sample-to-sample reproducibility as well. The experimental results were supported by finite-difference time domain (FDTD) simulations. Our study suggests that low-cost, large-scale, and uniform SERS substrates with a high EF and low detection limit can be achieved by using bottom-up chemical methods.

Electrostatically assisted fabrication of silver–dielectric core/shell nanoparticles thin film capacitor with uniform metal nanoparticle distribution and controlled spacing

An electrostatically-assisted strategy for fabrication of thin film composite capacitors with controllable dielectric constant (k) has been developed. The capacitor is composed of metal–dielectric core/shell nanoparticle (silver/silica, Ag@SiO2) multilayer films, and a backfilling polymer. Compared with the simple metal particle-polymer mixtures where the metal nanoparticles (NP) are randomly dispersed in the polymer matrix, the metal volume fraction in our capacitor was significantly increased, owing to the densely packed NP multilayers formed by the electrostatically assisted assembly process. Moreover, the insulating layer of silica shell provides a potential barrier that reduces the tunneling current between neighboring Ag cores, endowing the core/shell nanocomposites with a stable and relatively high dielectric constant (k) and low dielectric loss (D). Our work also shows that the thickness of the SiO2 shell plays a dominant role in controlling the dielectric properties of the nanocomposites. Control over metal NP separation distance was realized not only by variation the shell thickness of the core/shell NPs but also by introducing a high k nanoparticle, barium strontium titanate (BST) of relatively smaller size (∼8nm) compared to 80–160nm of the core/shell Ag@SiO2 NPs. The BST assemble between the Ag@SiO2 and fill the void space between the closely packed core/shell NPs leading to significant enhancement of the dielectric constant. This electrostatically assisted assembly method is promising for generating multilayer films of a large variety of NPs over large areas at low cost.