Nucleation Of Silver Nanoparticles Research Articles

Controlling silver release from antibacterial surface coatings on stainless steel for biofouling control

This study focuses on the in-situ nucleation of silver nanoparticles (AgNPs) on stainless steel (SS) to provide a localized antibacterial action for biofouling control during space missions. Since AgNPs rapidly dissolve in water, partial passivation of AgNPs was provided to slow down silver release and extend the lifetime of the antibacterial coating. Two different passivation approaches, based on the formation of low solubility silver sulfide (Ag2S) or silver bromide (AgBr) shells, were compared to identify the optimal passivation for biofouling control. Highest bacterial inactivation (up to 75%) occurred with sulfidized AgNPs as opposed to bromidized (up to 50%) NPs. The optimal passivation treatment for biofouling control was found at 10−5 M Na2S (for Ag2S) and 10−3 M NaBr (for AgBr) concentrations. Scanning Electron Microscopy (SEM) analyses confirmed the presence of AgNPs on AgBr and Ag2S-coated samples. Further investigation revealed that compared to pristine AgNPs, Ag release from both sulfidized and bromidized NPs was significantly lower (16% vs 6% or less). Overall, both sulfidized and bromidized AgNPs were effective at controlling biofilm formation; however, sulfidized NPs exhibited the maximum antibacterial activity, making it the preferable passivation strategy for AgNPs on SS surfaces.

Latex mediated green synthesis of silver nanoparticles and its antibacterial evaluation

A functional role of plant latex extract in the growth and nucleation of silver nanoparticles synthesized by green method has been discussed. By varying the biological species as capping and reducing agents, silver nanoparticles (AgNPs) of different morphologies under similar reaction conditions were produced. The synthetic protocol involves the preparation of AgNPs derived from two plant latex extract i.e. plumeria obtusa and manilkara zapota. Synthesized AgNPs generate the surface plasmonic resonance peak at 435 nm in UV–Visible spectrophotometer. Fourier-transform infrared spectroscopy (FT-IR) analysis shows the major role of active phenolic constituents and protein in reduction and stabilization of AgNPs. Size and shape of AgNPs were characterized through transmission electron microscopy (TEM) which shows that the AgNPs are of spherical form and relatively uniform. X-ray diffraction (XRD) pattern of AgNPs corresponding to (111), (200), (220) and (311) planes reveals that the generated nanoparticles were face centered cubic crystalline in nature. The average crystalline size was found to be 32.97 and 35.15 nm for plumeria obtusa and manilkara zapota respectively. The role of capping agents in controlling the size and properties of silver nanoparticles has been studied. Phyto-fabricated AgNPs exhibit significant antimicrobial activity against Staphylococcus aures and Escherichia coli.

Heterogeneous nucleation in citrate synthesis of AgNPs: Effect of mixing and solvation dynamics

The heterogeneity issues in silver nanoparticle nucleation (Lee-Meisel route) have been investigated. The final polydispersity and sphericity of the nanoparticles in the Lee-Meisel scheme are shown to depend upon the early time dynamics of silver-citrate complexation. The formation of macromolecular intermediary complexes in the early stages of the reaction is visualized based on online DLS data, TEM analysis, and the mass balances of silver and citrate ions. The reversible complexation between citrate ions and silver citrate is shown to be the limiting step that governs the directional growth of the nanoparticles. The dynamics of the complexation of citrate are seen to form a very rapid step and intense mixing was required for the complexation to happen uniformly across the reaction. This specific observation is also confirmed from the MD simulations. Thus, to get particles of high sphericity, irrespective of the reaction concentration, temperature, or reactor geometry, the mixing time should be <4 s and Da ~ 0.1. Optimal mixing conditions for isotropic growth are suggested based on the reaction kinetics and are also demonstrated with experimental evidence.

Nucleation of Tiny Silver Nanoparticles by Using a Tetrafacial Organic Molecular Barrel: Potential Use in Visible-Light-Triggered Photocatalysis.

Coordination-driven self-assembly of discrete molecular architectures of diverse shapes and sizes has been well studied in the last three decades. Use of dynamic imine bonds for designing analogous metal-free architectures has become a growing challenge recently. This article reports an organic molecular barrel (OB4R ) as a potential template for nucleation and stabilization of very tiny (<1.5 nm) Ag nanoparticles (AgNPs). Imine bond condensation of a rigid tetra-aldehyde with a flexible diamine followed by imine-bond reduction yielded the discrete tetragonal organic barrel (OB4R ). The presence of a molecular pocket ornamented with eight diamine moieties gives the potential for encapsulation of silver(I). The organic barrel was finally used as a molecular vessel for the controlled nucleation of silver nanoparticles (AgNPs) with fine size tuning through binding of AgI ions in the confined space of the barrel followed by reduction. Transmission electron microscopy (TEM) analysis of the Ag0 @OB4R composite revealed that the mean particle size is 1.44±0.16 nm. The composite material has approximately 52 wt % silver loading. The barrel-supported ultrafine AgNPs [Ag0 @OB4R ] are found to be an efficient photocatalyst for facile Ullmann-type aryl-amination coupling of haloarenes at ambient temperature without using any additives. The catalyst was stable for several cycles of reuse without any agglomeration. The new composite Ag0 @OB4R represents the first example of discrete organic barrel-supported AgNPs employed as a photocatalyst in Ullmann-type coupling reactions at room temperature.

Impact of thermal annealing time on luminescence properties of Eu3+ ions in silver nanoparticles embedded lanthanum sodium borate glasses

Eu3+ ions doped Ag NPs embedded glasses have been prepared in a glass composition (80-x-y)B2O3-15Na2O-5La2O3-xEu2O3-yAgCl (where × = 0.0, 0.5 mol% and y = 0.1 mol%) by a well-known conventional melt quenching method. Tuning of the surface plasmon resonance band and the nucleation of silver nanoparticles (Ag NPs) was controlled by a thermal annealing schedule. Annealed samples displayed a broad surface plasmon resonance band positioned at 426 nm and its intensity gradually increases with increasing annealing time. HR-TEM micrographs reveal the formation of spherical Ag NPs inside the glass system with an average particle size around 6 nm (for annealed samples). The structural characterizations FESEM and EDX measurements has been also carried out. Photoluminescence (PL) excitation and emission spectra were recorded for studied glasses. The optimum PL enhancement of the Ag NPs embedded glass system was obtained at 10 h of heat treatment and subsequently PL intensity decreased beyond 10 h annealing time (PL quenching was observed). Photoluminescence results reveal that the improvement in the PL intensity of Eu3+ ions is predominantly due to the local field effect attributed by the silver NPs and the PL intensity quenching of Eu3+ ions attributed to the resonance energy transfer from Eu3+ ions to silver nanoparticles. Judd-Ofelt theory has been used to calculate the radiative parameters like intensity parameters, radiation transition probabilities, branching ratios and radiative lifetimes of Eu3+ ions. The calculated radiative parameters and luminescence studies suggested that the investigated 10 h annealed glass system was practically appropriate material for the development of LEDs and solid state lasers.

Enhancing the Nonlinear Optical Properties of Lithium Tetraborate Glass Using Rare Earth Elements and Silver Nanoparticles

In recent years, nonlinear optics field is in constant growth, particularly on the characterization and study of optical properties of glass compounds. In this sense, the plasmonic effect caused by silver nanoparticles (SNP) on the nonlinear optical (NLO) properties of different materials was studied. Furthermore, we report the experimental absorption spectra, the emission spectra, Z-scan measurements in both closed and open apertures and scanning transmission electron microscopy (STEM) to show the morphology of the matrices and the nucleation of SNP. Moreover, some NLO parameters were calculated, such as the NL refraction index and NL coefficient absorption of lithium tetraborate (Li2B4O7) glass activated with rare earths (Dy3+ and Yb3+), as well as study of the effect of different concentrations of SNP. From the results obtained, it has been ascertained that the plasmon resonance caused by the presence of SNP enhances the NL refraction index value, as well as most of its linear optical properties in the matrix of Li2B4O7.

Nanoscale Mapping of Nonuniform Heterogeneous Nucleation Kinetics Mediated by Surface Chemistry.

Nucleation underlies the formation of many liquid-phase synthetic and natural materials with applications in materials chemistry, geochemistry, biophysics, and structural biology. Most liquid-phase nucleation processes are heterogeneous, occurring at specific nucleation sites at a solid-liquid interface; however, the chemical and topographical identity of these nucleation sites and how nucleation kinetics vary from site-to-site remain mysterious. Here we utilize in situ liquid cell electron microscopy to unveil counterintuitive nanoscale nonuniformities in heterogeneous nucleation kinetics on a macroscopically uniform solid-liquid interface. Time-resolved in situ electron microscopy imaging of silver nanoparticle nucleation at a water-silicon nitride interface showed apparently randomly located nucleation events at the interface. However, nanometric maps of local nucleation kinetics uncovered nanoscale interfacial domains with either slow or rapid nucleation. Interestingly, the interfacial domains vanished at high supersaturation ratio, giving way to rapid spatially uniform nucleation kinetics. Atomic force microscopy and nanoparticle labeling experiments revealed a topographically flat, chemically heterogeneous interface with nanoscale interfacial domains of functional groups similar in size to those observed in the nanometric nucleation maps. These results, along with a semiquantitative nucleation model, indicate that a chemically nonuniform interface presenting different free energy barriers to heterogeneous nucleation underlies our observations of nonuniform nucleation kinetics. Overall, our results introduce a new imaging modality, nanometric nucleation mapping, and provide important new insights into the impact of surface chemistry on microscopic spatial variations in heterogeneous nucleation kinetics that have not been previously observed.

Surface modification of titanium surfaces through a modified oxide layer and embedded silver nanoparticles: Effect of reducing/stabilizing agents on precipitation and properties of the nanoparticles

The final goal of this research is to produce a modified titanium surface simultaneously able to induce bone tissue integration in the case of critical bone quality and/or quantity (elderly population) and to prevent infections at the implant site and around it. A metallic antibacterial agent is used against bacteria colonization and biofilm formation, in agreement with the well-established strategy to reduce the use of antibiotics. A surface treatment able to induce the formation of a chemically modified and nanotextured surface oxide layer (with several functionalities suitable for fast and effective osseointegration), as well as the nucleation of silver nanoparticles on the surface was developed. The present paper aims to optimize the chemical process for the preparation of the modified surfaces. This paper describes the selection and dose of the required additives, such as reducing agents and nanoparticle stabilizers, in order to achieve a good control of the series of chemical reactions concurrently occurring during the surface chemical treatment. Surface topography (oxide nanotexture and nanoparticle precipitation) was investigated by means of Field Emission Scanning Electron Microscopy (FESEM) equipped with Energy Dispersive Spectroscopy (EDS) for semi-quantitative evaluation of the chemical composition. Silver release was measured in ultrapure water through a photometric method and surface ability to induce in vitro apatite precipitation was investigated by soaking in Simulated Body Fluid (SBF) followed by FESEM-EDS observations. Finally, a preliminary test of antibacterial activity of the modified titanium surfaces was carried out by means of both inhibition halo and adhesion assays against Staphylococcus aureus.

Modifying and Fine Controlling of Silver Nanoparticle Nucleation Sites and SERS Performance by Double Silicon Etching Process

Different forms of modified and well-controlled plasmonic silver nanoparticles (AgNPs) were synthesized by silver ion reduction process of porous silicon (PS). Fine control of PS surface morphology was accomplished by employing two etching processes: light-induced etching (LIE) and photo electrochemical etching (PECE). The idea was to prepare excellent and reproducible surface-enhanced Raman scattering (SERS) substrates with high enhancement performance. PS surface modification was employed to create efficient and nearly uniformly distributed AgNP hotspot regions with very high specific surface areas. Reproducibility deviation of no more than 5% and enhancement factor of 1.2 × 1014 were obtained by SERS measurements at very low, rhodamine 6G (R6G) dye, concentration 10−15 M. The PS morphology SERS substrate was well discussed and analyzed using field emission scanning electron microscopy (FE-SEM), X-ray diffraction spectroscopy (XRD), and Raman measurements.

Silver Nanoparticle Formation on Metal Substrate Under Concentration-Limited Condition

Silver nanoparticles were electrodeposited from 0.3 M oxalic acid electrolyte on a pure aluminum working electrode under silver ion concentration-limited condition. A silver wire was held in a glass tube containing 1.0 M KCl solution as the counter electrode. Ion exchange between the glass tube and the main electrodeposition bath through a capillary was driven by the overpotentials as high as 10 V supplied by an electrochemical workstation. Due to the reaction between chlorine anion and silver cation to form AgCl solid at the Ag/AgCl electrode, the silver ion concentration-limited condition holds in the electrolyte. It is found that silver grows at the aluminum working electrode to form nanoparticles with an average size of about 52.4 ± 13.6 nm. With the increasing of the deposition time, the silver nanoparticles aggregate into clusters. The silver particle clusters are separated with approximately 112.6 ± 19.7 nm due to the hydrogen bubble-induced self-assembling, which is shown by the confined deposition of silver on a gold coating. The surface roughness of the aluminum substrate leads to the reduced uniformity of silver nanoparticle nucleation and growth.

Electrochemical Study and Applications of Selective Electrodeposition of Silver on Quantum Dots.

In this work, selective electrodeposition of silver on quantum dots is described. The particular characteristics of the nanostructured silver thus obtained are studied by electrochemical and microscopic techniques. On one hand, quantum dots were found to catalyze the silver electrodeposition, and on the other hand, a strong adsorption between electrodeposited silver and quantum dots was observed, indicated by two silver stripping processes. Nucleation of silver nanoparticles followed different mechanisms depending on the surface (carbon or quantum dots). Voltammetric and confocal microscopy studies showed the great influence of electrodeposition time on surface coating, and high-resolution transmission electron microscopy (HRTEM) imaging confirmed the initial formation of Janus-like Ag@QD nanoparticles in this process. By use of moderate electrodeposition conditions such as 50 μM silver, -0.1 V, and 60 s, the silver was deposited only on quantum dots, allowing the generation of localized nanostructured electrode surfaces. This methodology can also be employed for sensing applications, showing a promising ultrasensitive electrochemical method for quantum dot detection.

Supported Silver Nanoparticle and Near-Interface Solution Dynamics in a Deep Eutectic Solvent

Type III deep eutectic solvents (DES) have attracted significant interest as both environmentally friendly and functional solvents that are, in some ways, advantageous to traditional aqueous systems. While these solvents continue to produce remarkable thin films and nanoparticle assemblies, their interactions with metallic surfaces are complex and difficult to manipulate. In this study, the near-surface region (2–600 nm) of a carbon surface is investigated immediately following silver nanoparticle nucleation and growth. This is accomplished, in situ, using a novel grazing transmission small-angle X-ray scattering approach with simultaneous voltammetry and electrochemical impedance spectroscopy. With this physical and electrochemical approach, the time evolution of three distinct surface interaction phenomena is observed: aggregation and coalescence of Ag nanoparticles, multilayer perturbations induced by nonaggregated Ag nanoparticles, and a stepwise transport of dissolved Ag species from the carbon surface. The multilayer perturbations contain charge-separated regions of positively charged choline-ethylene and negatively charged Ag and Cl species. Both aggregation-coalescence and the stepwise decrease in Ag precursor near the surface are observed to be very slow (∼2 h) processes, as both ion and particle transport are significantly impeded in a DES as compared to aqueous electrolytes. Altogether, this study shows how the unique chemistry of the DES changes near the surface and in the presence of nanoparticles that adsorb the constituent species.

Silver deposition directed by self-assembled gold nanorods for amplified electrochemical immunoassay

A novel electrochemical immunoassay was developed based on the signal amplification strategy of silver deposition directed by gold nanorods (AuNRs), which was in-situ assembled on the sandwich immunocomplex. The superstructure formed by the self-assembly of AuNRs provided abundant active sites for the nucleation of silver nanoparticles. In this pathway, the stripping current of silver was greatly enhanced. Using human immunoglobulin G (HIgG) as a model analyte, the ultrasensitive immunoassay showed a wide linear range of six orders of magnitude from 0.1 fg mL−1 to 100 pg mL−1, with the low detection limit down to 0.08 fg mL−1. The practicality of this electrochemical immunoassay for detection of HIgG in serum was validated with the average recovery of 93.9%. In addition, this enzyme-free immunoassay also has the advantages of acceptable reproducibility and specificity, and thus this immunosensing protocol can be extended to the detection of other low-abundant protein biomarkers.

Paper-based plasmon-enhanced protein sensing by controlled nucleation of silver nanoparticles on cellulose

Cheap, disposable bio-diagnostic devices are becoming increasingly prevalent in the field of biosensing. Earlier we had reported the ability of cellulosic surface to control the nucleation of plasmonic silver nanoparticles and in this report we utilize this nucleation controlling property to demonstrate a new plasmonic sensing mechanism based on paper substrates to quantitatively detect proteins. On contrary to conventional paper based diagnostic devices which use the cellulosic part of paper as a support structure, the proposed method takes advantage of cellulose as nucleation controller during silver nanoparticle formation. Reduction of silver ions interacting competitively with nucleation controlling cellulosic surface and reduction suppressing amino acids of protein (via complexation) resulted in silver nanoparticles whose size–shape dependent plasmonic property quantitatively reflected the concentration of protein on paper, characterized using UV–Vis and surface-enhanced Raman spectroscopies. As a proof-of-concept, bovine serum albumin (BSA) was tested as the target analyte. UV–Vis spectroscopy based BSA quantification was sensitive in the concentration range 10–60 mg ml−1 while that for surface enhanced Raman spectroscopy extended well below 10 mg ml−1, thus demonstrating the potential of this simple method to quantitatively detect a wide range of proteins relevant to the field of biodiagnostics.

Aligning Silicon Nanopillar Formed in Electroless HF/H2O2 Etching through Pre-Forming Porous Layer

For fabricating a controllable nanopillar array structure by utilizing the metal-assisted etching technique, we created a fine porous cladding layer on the surface of bulk silicon to settle down silver nanoparticles. Prior to metal-assisted etching process, a 10nm thick porous silicon layer was produced on the surface of a p-type, 1-10 Ohm-cm, (100) bulk silicon by HF based electrochemically etching and then rinsed by D.I. water. After spin-drying, the specimen and a same silicon specimen but without the porous layer were dipped in a solution (HF / AgNO3 / H2O) for 30 seconds for the nucleation of silver nanoparticles. The dipped specimens were then etched by HF/ H2O2/ H2O solution for forming nanopillar. Through the observation of Field Emission Scanning Electronic Microscopy (FE-SEM), we found the pores on the surface of the porous layer could provide priority nucleation sites for silver nanoparticles. Hence, we could achieve a designed silicon nanopillar array by controlling the formation of the porous layer. After etching, the silicon specimen with the pre-forming porous layer exhibits different characteristic from the one without the layer as shown in figure. Figure 1

Amphiphilic polyoxometalates for the controlled synthesis of hybrid polystyrene particles with surface reactivity.

Amphiphilic organo-polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50-100 nm polystyrene-POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM-mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.

Effects of irradiation defects on the nucleation of silver nanoparticles in spinel

Composites with embedded metal nanoparticles attract much interest due to their unique physical properties, which considerably depend on size and shape of the nanoparticles, and on interparticle distance and dispersity of these parameters. Crystal defects can have an effect on the nucleation of nanoparticles. In this paper, the effect of defects on the nucleation and growth of silver nanoparticles was investigated. Argon ions with kinetic energy of 110 keV were implanted into spinel crystals, to produce defects in the surface-near region, and silver ions were then implanted into the region rich in defects. UV–VIS spectroscopy and TEM were used to analyze the samples. It is found that the introduction of defects can enhance the nucleation of silver nanoparticles and mediate their size distribution, and that the size of these nanoparticles for the sample with argon pre-implantation is larger than that in the sample without argon pre-implantation. During an annealing process, defects can improve the growth efficiency of nanoparticles.

Strategies for specifically directing metal functionalization of protein nanotubes: constructing protein coated silver nanowires

Biological molecules that self-assemble in the nanoscale range are useful multifunctional materials. Rotavirus VP6 protein self-assembles into tubular structures in the absence of other rotavirus proteins. Here, we present strategies for selectively directing metal functionalization to the lumen of VP6 nanotubes. The specific in situ metal reduction in the inner surface of nanotube walls was achieved by the simple modification of a method previously reported to functionalize the nanotube outer surface. Silver nanorods and nanowires as long as 1.5 μm were formed inside the nanotubes by coalescence of nanoparticles. Such one-dimensional structures were longer than others previously obtained using bioscaffolds. The interactions between silver ions and the nanotube were simulated to understand the conditions that allowed nanowire formation. Molecular docking showed that a naturally occurring arrangement of aspartate residues enabled the stabilization of silver ions on the internal surface of the VP6 nanotubes. This is the first time that such a spatial arrangement has been proposed for the nucleation of silver nanoparticles, opening the possibility of using such an array to direct functionalization of other biomolecules. These results demonstrate the natural capabilities of VP6 nanotubes to function as a versatile biotemplate for nanomaterials.

Frequency upconversion in Nd3+ doped PbO–GeO2 glasses containing silver nanoparticles

Abstract Infrared-to-visible frequency upconversion (UC) in Nd3+-doped PbO–GeO2 (PGO) glasses containing silver nanoparticles (NPs) was investigated. The excitation was made at 805 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. Photoluminescence (PL) bands centered at 535 nm, 600 nm and 670 nm were observed corresponding to the electronic transitions 4G7/2 → 4I9/2, [4G7/2 → 4I11/2, 4G5/2 → 4I9/2], and [4G7/2 → 4I13/2, 4G5/2 → 4I11/2], respectively. The quadratic dependence of the UC intensity versus the laser intensity indicates that two laser photons contribute for the emission of each upconverted photon. The results show for the first time that the nucleation of silver NPs in Nd3+-doped PGO glasses contributes to increase the UC efficiency and the PL enhancement reached ≈50% for the samples with the maximum concentration of NPs.

Metal Fe3+ ions assisted synthesis of highly monodisperse Ag/SiO2 nanohybrids and their antibacterial activity

Highly monodispersed Ag/SiO2 nanohybrids with excellent antibacterial property were synthesized by using DMF as a reducing agent and employing an additional redox potential of metal Fe3+ ion as a catalytic agent. The obtained Ag/SiO2-2 nanohybrids of about 240nm were highly monodispersity and uniformity by adding trace Fe3+ ions into the reaction which Ag+ reacted with N,N-dimethyl formamide (DMF) at 70°C. Compared to the conventional techniques, which need long time and high temperature for silica coating of Ag nanoparticles, this new method was capable of synthesizing monodispersed, uniform, high yield Ag/SiO2 nanohybrids. The electron was transferred from the Fe2+ ion to the Ag+ ion to accelerate the nucleation of silver nanoparticles. The chemical structures, morphologies and properties of the Ag/SiO2 nanohybrids were characterized by X-ray diffraction (XRD), (High-resolution, Scanning transmission) transmission electron microscopy (TEM, HRTEM and STEM), and X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy (UV–vis) and test of antibacterial. The results demonstrated that the silver nanoparticles supported on the surface of SiO2 spheres in Ag/SiO2-2 nanohybrids structure, the Ag nanoparticles were homogeneous and monodispersed. The results also indicated that the Ag/SiO2-2 nanohybrid had excellent antibacterial.