Ag Dendrites Research Articles

Ag@Au core-shell dendrites: a stable, reusable and sensitive surface enhanced Raman scattering substrate.

Surface enhanced Raman scattering (SERS) substrate based on fabricated Ag@Au core-shell dendrite was achieved. Ag dendrites were grown on Si wafer by the hydrothermal corrosion method and Au nanofilm on the surface of Ag dendritic nanostructure was then fabricated by chemical reduction. With the help of sodium borohydride in water, Au surface absorbates such as thiophene, adenine, rhodamine, small anions (Br– and I–), and a polymer (PVP, poly(N-vinylpyrrolidone)) can be completely and rapidly removed. After four repeatable experiments, the substrate SERS function did not decrease at all, indicating that the Ag@Au dendrite should be of great significance to SERS application because it can save much resource. Six-month-duration stability tests showed that the Ag@Au core-shell dendrite substrate is much more stable than the Ag dendrite substrates. We have also experimented on fast detection of Cd2+ at 10−8 M concentration by decorating single-stranded DNA containing adenine and guanine bases on the surface of this Ag@Au dendrite. Finite-difference time-domain simulations were carried out to investigate the influence of Au nanolayer on Ag dendrites, which showed that the local electric fields and enhancement factor are hardly affected when a 4 nm Au nanolayer is coated on Ag dendrite surface.

Functionalizing Aluminum Oxide by Ag Dendrite Deposition at the Anode during Simultaneous Electrochemical Oxidation of Al.

A novel synthesis strategy is presented for depositing metallic Ag at the anode during simultaneous electrochemical oxidation of Al. This unexpected result is achieved based on galvanic coupling. Metallic dendritic nanostructures well-anchored in a high surface area supporting matrix are envisioned to open up a new avenue of applications.

Reversible Liquid Adhesion Switching of Superamphiphobic Pd-Decorated Ag Dendrites via Gas-Induced Structural Changes

Adhesion control of various liquid droplets on a liquid-repellent surface is a fundamental technique in novel open channel microfluidic systems. Herein, we demonstrate reversible liquid droplet adhesion switching on superamphiphobic Pd-decorated Ag dendrites (Pd/Ag dendrites). Although adhesion between liquids and the superamphiphobic surfaces was extremely low under ambient air, high adhesion was instantly achieved by exposure of the dendrites to 8% hydrogen gas. Transition from low to high adhesion and the reverse case were successfully repeated more than 10 times by switching from atmospheric ambient air to 8% hydrogen gas. This is the first technique that allows real-time reversible adhesion change with various liquid droplets to a surface using gas-induced structural changes and can potentially be used to realize various functions for droplet-based microfluidics.

Fabrication of an electrochemical sensor based on computationally designed molecularly imprinted polymer for the determination of mesalamine in real samples.

A novel electrochemical sensor based on mesalamine molecularly imprinted polymer (MIP) film on a glassy carbon electrode was fabricated. Density functional theory (DFT) in gas and solution phases was developed to study the intermolecular interactions in the pre-polymerization mixture and to find the suitable functional monomers in MIP preparation. On the basis of computational results, o-phenylenediamine (OP), gallic acid (GA) and p-aminobenzoic acid (ABA) were selected as functional monomers. The MIP film was cast on glassy carbon electrode by electropolymerization of solution containing ternary monomers and then followed by Ag dendrites (AgDs) with nanobranch deposition. The surface feature of the modified electrode (AgDs/MIP/GCE) was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Under the optimal experimental conditions, the peak current was proportional to the concentration of mesalamine ranging from 0.05 to 100 μM, with the detection limit of 0.015 μM. The proposed sensor was applied successfully for mesalamine determination in real samples.

Effects of Preparation on the Silicon Nanowires Grown By Electroless Etching

Highly oriented SiNWs arrays prepared by electroless etching method can significantly suppress light reflection across a broad spectrum [1]. The antireflective nature of Silicon nanowires (SiNW’s) revealed by their black color and dull appearances have drawn the attention of researchers [2]. Reflectivity studies on these show a significantly decrease in optical reflectivity down to 1.3% for 10 µm long SiNWs arrays [3]. Electroless etching is a top-down technique for growing SiNWs and does not need costly and expensive equipment to grow SiNWs as bottom-up methods usually do. The electroless process begins with the cleaning of silicon substrates. They were cleaned in acetone, methanol and deionized water, then blow-dried with N2. They are dipped in hydrofluoric acid (HF) 49% solution for 1 min to remove any remaining oxide. The silicon (Si) wafers are dipped for 15 minutes at room temperature in an electroless solution prepared in a petri dish containing silver nitrate (AgNO3) and hydrofluoric acid (HF) [4]. The substrates are dipped and galvanic reactions disperse silver ions on their surface, losing silicon as SiF6. As a consequence of this etching process, the removal of Si via Ag ions results in vertically aligned arrays of SiNWs covered with silver dendrites. At the end of the etching process, the samples were dipped in two baths of deionized water and placed in diluted nitric acid (HNO3) 20% to remove the Ag dendrite layer formed on top of the SiNW arrays. Reflectance on different methods to remove the residual silver particles from SiNW’s when using an unstirred, stirred and sonicated diluted nitric acid (HNO3) 20% solution are presented Fig 1. Figure 1

Galvanic replacement synthesis of silver dendrites-reduced graphene oxide composites and their surface-enhanced Raman scattering characteristics

A simple method was developed to synthesize Ag dendrites/reduced graphene oxide (AgD/RGO) composites based on the galvanic displacement method. AgNO3 was used as the precursor for Ag dendrites and aluminum foils served as the sacrifice metal. The as-synthesized AgD/RGO composite was characterized by SEM, FTIR, UV–vis spectroscopy and Raman spectroscopy. The results showed that the graphene oxide was successfully incorporated into the Ag dendritic structure and was reduced during the galvanic displacement between Ag+ ions and the aluminum foil. XRD analysis revealed that the Ag formed in the composite was in the cubic phase. The surface-enhanced Raman scattering (SERS) property of the as synthesized AgD/RGO composite was evaluated using Rhodamine B as a probe. The composite deposited substrate exhibited a much higher SERS activity compared with substrates modified with Ag dendrites or GO, indicating that the AgD/RGO could potentially be used as a highly sensitive SERS substrate for molecule detecting applications.

Growth of giant silver dendrites on layer-by-layer assembled films

Ag dendrites were previously synthesized, with limited success, via the chemical reduction of Ag+ ions with a soluble reducing agent in homogeneous solutions. Here Ag+ ions were first loaded in hydrogen-bonded layer-by-layer (LBL) films fabricated from poly(vinyl pyrrolidone) (PVPON) and poly(acrylic acid) (PAA), then reduced chemically using p-hydroquinone (HQ) as a reducing agent to afford Ag dendritic structures. The dendrites were characterized by SEM, TEM, XRD and optical microscope. Compared with the Ag dendrites synthesized in homogenous solutions, the dendrites obtained here are much larger. The fully developed ones can reach a size over 600 μm, ca. 2 orders of magnitude larger than those synthesized in homogenous solutions (∼1–5 μm). In addition, the dendrites obtained here are 2 dimensional which grow along the surface of the LBL film, instead of 3 dimensional as those obtained in homogenous solutions. A possible 3-step growth mechanism, which involves the rapid reduction of the Ag+ ions in the film, formation of Ag seed particles on the film surface, and fractal dendritic structure formation as described by the diffusion-limited aggregation (DLA) model, was proposed.

A facile formation of silver dendrites on indium tin oxide surfaces using electrodeposition and amperometric sensing of hydrazine

Silver dendritic structures have been prepared using constant potential deposition on indium tin oxide (ITO) electrodes from an aqueous solution of AgNO3 and KNO3 without any surfactants or structure directing agents. The applied potential is shown to be a crucial factor in the formation of dendrites. Depending upon the magnitude of the applied potentials, morphologies vary from polygons to dendrites. The shape evolution of the silver dendrites has been investigated by varying the deposition time and metal precursors. The mechanism of formation of dendrites is interpreted using the diffusion limited aggregation (DLA) model. The fractal dimensions of the dendrites calculated using the box counting algorithm are in agreement with those predicted by the DLA model. The Ag dendrites coated ITO electrodes exhibit excellent electrocatalytic activity toward oxidation of hydrazine in alkaline medium. The sensing of hydrazine is carried out with amperometry, where from the limit of detection and linear calibration range is deduced as 0.5μM and 100–1700μM respectively. The effect of ascorbic acid, urea, ethanol, glucose, K+, Cl−, Br− and I− ions as possible interfering agents in the detection of hydrazine is analyzed.

4-1BB ligand signaling to T cells limits T cell activation.

4-1BB ligand (4-1BBL) and its receptor, 4-1BB, are both induced on T cells after activation, but little is known about the role of 4-1BBL. In this study we show that 4-1BBL can transmit signals that limit T cell effector activity under tolerogenic conditions. Cross-linking 4-1BBL inhibited IL-2 production in vitro, primarily with suboptimal TCR stimulation. Furthermore, naive 4-1BBL-deficient OT-II transgenic T cells displayed a greater conversion to effector T cells in vivo when responding to soluble OVA peptide in wild-type hosts, whereas development of Foxp3(+) regulatory T cells was not altered. A greater number of effector T cells also differentiated from naive wild-type OT-II T cells when transferred into 4-1BB-deficient hosts, suggesting that APC-derived 4-1BB is likely to trigger 4-1BBL. Indeed, effector T cells that could not express 4-1BBL accumulated in larger numbers in vitro when stimulated with 4-1BB-expressing mesenteric lymph node dendritic cells. 4-1BBL was expressed on T cells when Ag presentation was limiting, and 4-1BBL was aberrantly expressed at very high levels on T cells that could not express 4-1BB. Trans-ligation, Ab capture, and endocytosis experiments additionally showed that T cell-intrinsic 4-1BB regulated internalization of membrane 4-1BBL, implying that the strong induction of 4-1BB on T cells may counteract the suppressive function of 4-1BBL by limiting its availability. These data suggest that 4-1BBL expressed on T cells can restrain effector T cell development, creating a more favorable regulatory T cell to effector cell balance under tolerogenic conditions, and this may be particularly active in mucosal barrier tissues where 4-1BB-expressing regulatory dendritic cells present Ag.

Randomly oriented twin domains in electrodeposited silver dendrites

Silver dendrites were prepared by electrochemical deposition. The structures of Ag dendrites, the type of twins and their distribution were investigated by scanning electron microscopy (SEM), Z-contrast high angle annular dark field transmission electron microscopy (HAADF), and crystallografically sensitive orientation imaging microscopy (OIM). The results revealed that silver dendrites are characterized by the presence of randomly distributed 180? rotational twin domains. The broad surface of dendrites was of the {111} type. Growth directions of the main dendrite stem and all branches were of <112> type.

Sensing trace arsenate by surface enhanced Raman scattering using a FeOOH doped dendritic Ag nanostructure

SERS based arsenic detection at ∼10−10M level with a FeOOH doped (3.5%) uniform dendritic Ag nanostructure. Area mapping shows the uniformity of the SERS substrate taking arsenate as the probe molecule.

Silver-assisted chemical etching on silicon with polyvinylpyrrolidone-mediated formation of silver dendrites.

Metal-assisted chemical etching (MaCE) on silicon (Si)-mediated by polyvinylpyrrolidone (PVP)-is systematically investigated herein. It is found that the morphologies and crystallographic natures of the grown silver (Ag) dendrites can be significantly modulated, with the presence of PVP in the MaCE process leading to the formation of faceted Ag dendrites preferentially along the (111) crystallographic phase, rather than along the (200) phase. Further explorations of the PVP-mediated effect on Si etching are also revealed. In contrast to the aligned Si nanowires formed by MaCE without PVP addition, only distributed nanopores with sizes of 200 to 400 nm appear on the Si surfaces in the presence of PVP. The origin of surface polishing on Si in the PVP-mediated MaCE process can be attributed to the distinct transport pathway of holes supplied by the Ag(+) ions, where the holes are injected directly into the primary Ag seeds, rather than through Ag dendrites, thus leading to the isotropic etching of the Si surface.

Application of bimetallic PtPd alloy decorated graphene in peroxydisulfate electrochemiluminescence aptasensor based on Ag dendrites decorated indium tin oxide device

In this paper, PtPd alloy decorated reduced graphene oxide (RGO/PtPd) was synthesized by a simple and green method. The RGO/PtPd could catalytic oxidation of H2O2 to form O2 and O2 acted as the coreactant of peroxydisulfate, could greatly amplify the ECL signal. Moreover, the RGO/PtPd exhibited higher catalytic activity compared to the RGO/Pt or RGO/Pd catalyst because of the synergetic effects of Pt and Pd and the enhanced electron transfer of RGO. Based on this, a highly sensitive and selective label-free electrochemiluminescence (ECL) aptasensor for detection of adenosine triphosphate was designed. In this process, RGO/PtPd could be regarded as mimicking enzyme, the effect of which was similar to horseradish peroxidase in generating O2 and also used as carriers to immobilize ssDNA2. With respect to sensitivity, Ag dendrites with hierarchical nanostructures were electrodeposited on working electrode of portable indium tin oxide device, which improved the electronic transfer rate as well as increased the amount of immobilized capture ssDNA1. Under the optimal conditions, the approach provided a linear range from 0.1pM to 50nM and a low detection limit of 0.037pM.

Dendritic Ag–Fe nanocrystalline alloy synthesized by pulsed electrodeposition and its characterization

Synthesis of dendrite shaped Ag–Fe alloy nanomaterial by pulsed electrodeposition route was investigated. The alloy samples were deposited at different current densities from electrolytes of different compositions to study the influence of current density and bath composition on metal contents in the alloy, which was determined by ICP-OES analysis. The XRD studies were carried out to determine the structure of these samples. Magnetic characterization at room temperature and during heating was carried out to understand their magnetic behaviour and to confirm the inferences drawn from the XRD results. The XPS spectra proved the presence of Fe and Ag in the metallic form in the alloy samples. The FESEM and TEM micrographs were taken to view the surface morphology of the nanosized particles.

Synthesis of Dendritic Silver Nanostructures on Al Foil by Galvanic Displacement for Catalytic Degradation of Methylene Blue

Silver dendrites were synthesized via a simple and straightforward strategy based on the galvanic displacement between Ag ions and aluminum foil in the room temperature. Because the presence of Al2O3 thin layer on the surface of aluminum foil, the NaCl was added to accelerates the reaction rate. The formed Ag dendrites was characterized by UV-vis spectroscopy, SEM and XRD. The as-prepared Ag dendrites were developed as a catalyst by mixed with reduced graphene oxide and used for degradation of methylene blue when the presence of NaBH4. Moreover, the optimal conditions of degradation were also investigated.

Targeting antigens through blood dendritic cell antigen 2 on plasmacytoid dendritic cells promotes immunologic tolerance.

The C-type lectin receptor blood dendritic cell Ag 2 (BDCA2) is expressed exclusively on human plasmacytoid DCs (pDCs) and plays a role in Ag capture, internalization, and presentation to T cells. We used transgenic mice that express human BDCA2 and anti-BDCA2 mAbs to deliver Ags directly to BDCA2 on pDCs in vivo. Targeting Ag to pDCs in this manner resulted in significant suppression of Ag-specific CD4(+) T cell and Ab responses upon secondary exposure to Ag in the presence of adjuvant. Suppression of Ab responses required both a decrease in effector CD4(+) T cells and preservation of Foxp3(+) regulatory T cells (Tregs). Reduction in Treg numbers following Ag delivery to BDCA2 restored both CD4(+) T cell activation and Ab responses, demonstrating that Tregs were required for the observed tolerance. Our results demonstrate that Ag delivery to pDCs through BDCA2 is an effective method to induce immunological tolerance, which may be useful for treating autoimmune diseases or to inhibit unwanted Ab responses.

B Cell Antigen Presentation in the Initiation of Follicular Helper T Cell and Germinal Center Differentiation

High-affinity class-switched Abs and memory B cells are products of the germinal center (GC). The CD4+ T cell help required for the development and maintenance of the GC is delivered by follicular Th cells (T(FH)), a CD4+ Th cell subset characterized by expression of Bcl-6 and secretion of IL-21. The cellular interactions that mediate differentiation of TFH and GC B cells remain an important area of investigation. We previously showed that MHC class II (MHCII)-dependent dendritic cell Ag presentation is sufficient for the differentiation of a T(FH) intermediate (termed pre-T(FH)), characterized by Bcl-6 expression but lacking IL-21 secretion. In this article, we examine the contributions of MHCII Ag presentation by B cells to T(FH) differentiation and GC responses in several contexts. B cells alone do not efficiently prime naive CD4+ T cells or induce T(FH) after protein immunization; however, during lymphocytic choriomeningitis virus infection, B cells induce T(FH) differentiation despite the lack of effector CD4+ T cell generation. Still, MHCII+ dendritic cells and B cells cooperate for optimal T(FH) and GC B cell differentiation in response to both model Ags and viral infection. This study highlights the roles for B cells in both CD4+ T cell priming and T(FH) differentiation, and demonstrates that different APC subsets work in tandem to mediate the GC response.

Lipid and lipid oxidation analysis using surface enhanced Raman spectroscopy (SERS) coupled with silver dendrites

Surface enhanced Raman spectroscopy (SERS) has been exploited widely for sensitive molecular characterization and has been used extensively as a signal transduction mechanism in biological and chemical sensing. However, little application has been explored in analyzing lipids, e.g. edible oils. In this study, we evaluated the SERS method coupled with silver (Ag) dendrites on the enhancement ability and analytical capacity of measuring canola oil and α-tocopherol. The feasibility of using this SERS method to analyze the oxidation process of canola oil was also investigated. Our results showed improved sensitivity when analyzing diluted canola oil and α-tocopherol using SERS, and the potential of analyzing these two components simultaneously in a mixture. Significant changes of SERS spectra were observed between the original canola oil and the oil incubated at 55°C for 5days by principal component analysis (PCA). Compared with conventional Raman measurement and UV absorbance measurement of conjugated diene, this SERS method was more sensitive to detect changes in lipid molecules during the oxidation process. This data suggests a great potential of using SERS for sensitive measurement of lipids and detection of lipid oxidation.

Versatile Ag dendrites: simple galvanostatic deposition and applications

Large Ag dendrites were rapidly deposited via a facile electrochemical route at a deposition current of 20 mA for 10 min in air at room temperature, employing a mixed system of AgNO3 and NH3·H2O as the electrolyte. The phase and morphology of the as-prepared product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and scanning electron microscopy (SEM). It was found that the original ammonia amount played a crucial role in the formation of Ag dendrites. Experiments showed that the as-deposited Ag dendrites exhibited versatile applications in some fields including super-SERS performance for the detection of rhodamine-6G, highly effective antimicrobial activities toward Escherichia coli and excellent catalytic capacities for the reduction of 4-nitrophenol to 4-aminophenol.

Chemical preparation and applications of silver dendrites

AbstractSilver dendrites have received immense attention because of their fascinating hierarchical structures and unique properties. Depending on the methods of synthesis, Ag dendrites can be implemented in numerous fields. This review summarizes a variety of Ag dendrites preparation techniques. The involved growth mechanisms are investigated in order to control the formation progress more effectively. With regard to the applications, this article mainly focuses on surface enhanced Raman spectroscopy, catalysis, superhydrophobic surface and surface enhanced fluorescence by using Ag dendrites. The remaining issues of the preparation methods, which impede the practical applications of Ag dendrites, are pointed out to enlighten their future research.