Silver Load Research Articles

Acoustic Vibration Modes of Gold–Silver Core–Shell Nanoparticles

Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling.

How colloidal surface additivation of polyamide 12 powders with well-dispersed silver nanoparticles influences the crystallization already at low 0.01 vol%

As Additive Manufacturing (AM) is fast-growing, properties adaption of feedstock materials for AM is becoming more and more relevant due to high quality standards in industrial applications. Compared to traditional manufacturing techniques like injection molding, laser powder bed fusion (PBF-LB) of polymers has a very limited variety of processable materials, which is a major obstacle for future growth. Nanocomposites are an established material class for addressing the limitations in PBF-LB but often show poor dispersion of the nanomaterial in/on the polymer powder. Especially in the context of plasmonic nanomaterials and composites, where the state of aggregation considerably influences the optical properties, dispersion plays an important role. Our study presents a deeper understanding of the colloidal surface additivation of polyamide 12 (PA12) powders with laser-generated plasmonic silver nanoparticles, leading to high dispersion of the nanoparticles on the micropowder surface with good reproducibility. The additivation is ruled by colloidal stability and control of electrostatic forces between particles and resulted in powders that could successfully be processed on a PBF-LB machine to generate plasmonic-functionalized parts. Finally, we introduce the surface specific nanoparticle dose (surf%) as scaling key parameter complementary to the commonly used mass specific dose (wt%) to appropriately describe nanoparticle load, proving the effect of such surface additivation on the recrystallization behavior of PA12. Via flash calorimetry, already at 0.01 vol% silver load, significant nanoparticle-induced heterogeneous nucleation effects are evident, whereas the thermal properties analyzed by conventional calorimetry remain unaffected.

Zeolites Modified with Silver Nanoparticles and Clusters: Synthesis, Characterization, and Catalytic Performance in H2 and CO Oxidation Reactions

Zeolites with Rho, Beta, and paulingite structures, modified with silver nanoparticles and clusters, are prepared, and their catalytic performances in hydrogen and carbon monoxide oxidation reactions are investiagted. The prepared zeolite samples have different silver loads (up to 25 wt %), and the loaded silver exists in the form of nanoparticles and clusters having a different nuclearity ( $$\rm{Ag_8^+},\rm{Ag_4^{2+}},\rm{Ag_4^+}$$ ). Silver clusters were detected and identified using UV−Vis spectroscopy. It is established that the catalytic performance of our silver-modified zeolites varies with the silver load, the form the loaded silver assumes (nanoparticles and/or clusters of a different nuclearity, and their ratio), and the structural type of zeolite matrix.

Preparation of effective Ag-loaded zeolite antibacterial materials by solid phase ionic exchange method

Ag-loaded antibacterial zeolite materials were prepared by a solid phase ionic exchange approach with small NaA zeolite crystals synthesized by sol–gel method as carrier, NH4NO3 and AgNO3 as raw materials. The influence of AgNO3 amount, reaction temperature, and reaction time on silver load in the zeolite was investigated. The phase composition and morphology of the Ag-loaded zeolite were also characterized. In addition, the antibacterial activity, sustained-release performance, and anti-tarnish property of the Ag-loaded zeolite were studied. The results show that the Ag-loaded zeolite was synthesized under optimum conditions. The amount of silver load in the zeolite was up to 23.45% (mass ratio). The minimum inhibitory concentration value (MIC value) was 9.17 ppm, and the diameter of inhibition zone for Escherichia coli was 16.3 mm. The MIC value was 12.50 ppm, and the diameter of inhibition zone for Staphylococcus aureus was 14.5 mm. Furthermore, the Ag-loaded zeolite materials demonstrate good sustained-release performance and anti-tarnish property.

Alginate and polyethyleneimine dually mediated synthesis of nanosilver-containing composites for efficient p-nitrophenol reduction

Three-dimensional silver/polyethyleneimine/alginate hydrogel beads have been prepared successfully via a facile and simple one-pot assembly method, which can be used efficiently in catalytic hydrogenation reaction of p-nitrophenol under batch and fixed-bed experiment. Polyethyleneimine is used to reduce and limit the growth of nano-silver particle and alginate microsphere is used as the catalyst carrier, leading to form well silver nanoparticles dispersion. Several characterizations were applied to the materials, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. As-prepared catalysts only spent 120s finishing reaction at ambient temperature (20% silver load) and stable catalytic performance with high conversion percentage for p-nitrophenol about 90% at 298K under fixed-bed condition. The relationship between concentration and time was well depicted by Pseudo-first order kinetic model. The catalytic performance for recycled catalyst remained highly efficient, and the conversion efficiency of 96.4% can be maintained after 10 cycles.

Synthesis and characterization of silver vanadates thin films for photocatalytic applications

Silver vanadates thin films were deposited by a hybrid deposition system combining laser ablation and thermal evaporation. A high purity vanadium target was ablated using the third harmonic of a Nd:YAG laser whereas high purity silver pellets were evaporated. The as-deposited thin films were subjected to thermal treatments at 400°C to obtain crystalline films. For films without Ag amorphous V2O5 thin films were deposited and as the Ag is incorporated in the material different silver vanadates were obtained. The effect of the silver load on the composition, structure, optical properties, surface morphology and photocatalytic response of the deposited films was studied. The film composition, determined by X-ray photoelectron spectroscopy, reveals Ag contents from 5.5 to 18.9 at.%. The crystalline phases formed were identified by micro-Raman Spectroscopy; the results indicate the formation of three silver vanadates depending on the silver content. The morphology was observed using scanning electron microscopy, the filḿs surface changes from a smooth surface to belts covering the surface and finally Ag nanoparticles are observed at the higher Ag contens. Optical properties determined from UV–vis reveal the presence of the surface plasmon signal in films containing silver. The films were tested in the photocatalytic degradation of Malachite Green dye reaching maximum degradations degrees close to 53% under solar irradiation. Reactive species trapping experiments suggest that O2− produced by the O2 reduction via the photogenerated electrons drives the photodegradation mechanism.

Mass Cytometry for Detection of Silver at the Bacterial Single Cell Level.

Background: Mass cytometry (Cytometry by Time of Flight, CyTOF) allows single-cell characterization on the basis of specific metal-based cell markers. In addition, other metals in the mass range such as silver can be detected per cell. Bacteria are known to be sensible to silver and a protocol was developed to measure both the number of affected cells per population and the quantities of silver per cell.Methods: For mass cytometry ruthenium red was used as a marker for all cells of a population while parallel application of cisplatin discriminated live from dead cells. Silver quantities per cell and frequencies of silver containing cells in a population were measured by mass cytometry. In addition, live/dead subpopulations were analyzed by flow cytometry and distinguished by cell sorting based on ruthenium red and propidium iodide double staining. Verification of the cells’ silver load was performed on the bulk level by using ICP-MS in combination with cell sorting. The protocol was developed by conveying both, fast and non-growing Pseudomonas putida cells as test organisms.Results: A workflow for labeling bacteria in order to be analyzed by mass cytometry was developed. Three different parameters were tested: ruthenium red provided counts for all bacterial cells in a population while consecutively applied cisplatin marked the frequency of dead cells. Apparent population heterogeneity was detected by different frequencies of silver containing cells. Silver quantities per cell were also well measurable. Generally, AgNP-10 treatment caused higher frequencies of dead cells, higher frequencies of silver containing cells and higher per-cell silver quantities. Due to an assumed chemical equilibrium of free and bound silver ions live and dead cells were associated with silver in equal quantities and this preferably during exponential growth. With ICP-MS up to 1.5 fg silver per bacterial cell were detected.Conclusion: An effective mass cytometry protocol was developed for the detection and quantification of silver in single bacterial cells of different physiological states. The silver quantities were generally heterogeneously distributed among cells in a population, the degree of which was dependent on micro-environmental conditions and on silver applied either in ion or nanoparticle-aggregated form.

Silver nanoparticles/ibuprofen-loaded poly(L-lactide) fibrous membrane: anti-infection and anti-adhesion effects.

Infection caused by bacteria is one of the crucial risk factors for tendon adhesion formation. Silver nanoparticles (AgNP)-loaded physical barriers were reported to be effective in anti-infection and anti-adhesion. However, high silver load may lead to kidney and liver damages. This study was designed for Ibuprofen (IBU)-loaded poly(l-lactide) (PLLA) electrospun fibrous membranes containing a low dosage of Ag to evaluate its potential in maintaining suitable anti-infection and good anti-adhesion effects. The in vitro drug release study showed a sustained release of Ag ions and IBU from the membrane. Inferior adherence and proliferation of fibroblasts were found on the Ag4%–IBU4%-loaded PLLA electrospun fibrous membranes in comparison with pure PLLA and 4% Ag-loaded PLLA membranes. In the antibacterial test, all Ag-loaded PLLA electrospun fibrous membranes prevented the adhesion of Staphylococcus aureus and Staphylococcus epidermidis. Taken together, these results demonstrate that Ibuprofen is effective in enhancing the anti-adhesion and anti-proliferation effects of 4% Ag-loaded PLLA fibrous membrane. The medical potential of infection reduction and adhesion prevention of Ag4%–IBU4%-loaded PLLA electrospun fibrous membrane deserves to be further studied.

Flexible PVDF-TrFE pyroelectric sensor driven by polysilicon thin film transistor fabricated on ultra-thin polyimide substrate

In this work we present a flexible pyroelectric sensor composed by a PVDF-TrFE capacitor realized on ultra-thin polyimide film (5μm thick), integrated with a n-channel low temperature polysilicon thin film transistor also fabricated on ultra-thin polyimide (8μm thick). Exploiting a multi-foil approach, the pyroelectric capacitors and the transistors were attached one over the other reaching a final thickness of about 15μm. The bottom contact of the sensor capacitance was connected to the gate of the transistor by a silver ink, while, for bias and load resistances, we used external elements. The active sensor area was defined by a circular capacitor with a diameter of about 2mm. In order to enhance PVDF-TrFE pyroelectric properties, an external stepwise voltage was applied to the structure up to values of 160V at a temperature of about 80°C. The devices were then tested, at different working frequencies (up to 800Hz) under a specific infrared radiation provided by a He–Ne laser, with a wavelength of 632nm and maximum power of 5mW. An output signal of tens of millivolt was observed at 10Hz, exploiting the pre-amplification of polysilicon thin film transistor.

Silver nanoparticles formation within unsaturated polyester/styrene resins induced by UV irradiation and thermal treatment

This article describes the formation of silver nanoparticles (NPs) within preformed unsaturated polyester/styrene resins in which the resulting color could be tuned by changing the silver load, time, and method used to grow the NPs. NP size and aggregation are responsible for the resulting sample color, and the samples present very good optical transparency. The silver ions were first added to the prepolymer that was crosslinked by free radical polymerization in the absence of light. NP formation was subsequently induced by submitting the transparent and colorless samples to heat or UV irradiation. Within the heated samples, isolated spherical particles ranging from 3 to 40 nm were observed. UV irradiation led to the formation of particle aggregates; however, as the exposure time was increased, silver NPs became well dispersed within the matrix within a particle diameter range of 9 to 24 nm. The particle formation is faster when induced by UV irradiation. Samples were also prepared by first dissolving rhodamine 6G in the resin. The emission bandwidth of samples prepared in this way showed a dependence on the silver particles amount and size. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Red Tide Inactivation by Silver Doped TiO<sub>2</sub> Produced in Sono-Chemistry Method

Nano-technology is a super microscopic technology to deal with the structures of 100 nm or smaller. This technology also involves the developing of TiO2 materials or TiO2 devices within that size. The aim of the present paper is to synthesize the silver doped nano-TiO2 by Sonochemistry method and to evaluate the effect of different percentages (0.2-1.5%) of silver load on TiO2 in the algae inactivation, The sample were characterized by using different techniques as XPS, TEM, SEM. Photo-catalytic activity of Silver doped TiO2 were evaluated through the inactivation of red tide (Cochlodinium) using UV-irradiation (315-400nm). The best result was found with silver doped TiO2.

An in vitro method for the quantitative determination of the antimicrobial efficacy of silver-containing wound dressings

Treatment with silver-containing wound dressings is becoming an increasingly popular strategy to eliminate growth of opportunistic wound pathogens during the healing process. However, there are concerns over the possible side-effects of silver to the patient; coupled to the cost of silver as an ingredient there is a desire to ensure that wound dressings contain the least quantity of active ingredient to ensure the minimum bactericidal concentration (MBC) of silver is maintained in the wound environment. This requires the ability to determine the efficacy of silver directly within the wound environment; an extremely complicated task that is difficult using classical (plate counting) microbiological assays because these cannot be conducted in situ. Here, we report a quantitative method for determining the efficacy of silver in wound dressings using an isothermal calorimetric method. The growth curves of P. aeruginosa (NCIMB 8628) were recorded in growth medium and in growth medium containing AQUACEL ® Ag Hydrofiber ® dressing. It was found that 10 mg of dressing was sufficient to ensure no detectable growth of organism in 2.5 mL of medium inoculated to 10 6 cfu/mL. This corresponded to a silver load of 1.1 × 10 −6 moles (equivalent to 4.4 × 10 −4 M, in the volume of medium used in the experiment). Experiments conducted with silver nitrate rather than dressing indicated the MBC of silver against P. aeruginosa was 1 × 10 −4 M. The results suggested that not all of the silver in the dressing was bioavailable, at least over the lifetime of the experiment. One advantage of this effect would be the lack of excess availability of the silver, which allays fears of potential toxicity to the patient and may provide an extended period of time over which the dressing is bactericidal.

Photochromic silver nanoparticles fabricated by sputter deposition

In this study a simple route to preparing photochromic silver nanoparticles in a TiO2 matrix is presented, which is based upon sputtering and subsequent annealing. The formation of silver nanoparticles with sizes of some tens of nanometers is confirmed by x-ray diffraction and transmission electron microscopy. The inhomogeneously broadened particle-plasmon resonance of the nanoparticle ensemble leads to a broad optical-absorption band, whose spectral profile can be tuned by varying the silver load and the annealing temperature. Multicolor photochromic behavior of this Ag–TiO2 system upon irradiation with laser light is demonstrated and discussed in terms of a particle-plasmon-assisted electron transfer from the silver nanoparticles to TiO2 and subsequent trapping by adsorbed molecular oxygen. The electron depletion in the nanoparticles reduces the light absorption at the wavelength of irradiation. A gradual recovery of the absorption band is observed after irradiation, which is explained with a slow thermal release of electrons from the oxygen trapping centers and subsequent capture into the nanoparticles. The recovery can be accelerated by ultraviolet irradiation; the explanation for this observation is that electrons photoexcited in the TiO2 are captured into the nanoparticles and restore the absorption band.

Effects of chloride, calcium, and dissolved organic carbon on silver toxicity: Comparison between rainbow trout and fathead minnows

AbstractThe effects of independently altering chloride, calcium, and dissolved organic carbon (DOC) on the toxicity of silver (presented as AgNO3) were compared between rainbow trout (Oncorhynchus mykiss) and fathead minnows (Pimephales promelas). The 96‐h median lethal concentration (LC50) toxicity tests for both species were performed under the same conditions, within the same containers. In addition, the effect of altering [Cl−] on silver‐induced perturbations to body Na+ influx and gill silver load was studied. Toxicity tests were conducted in synthetic soft water (50 μM Na+, 50 μM Cl−, 50 μM Ca2+, 0.3 mg DOC/L). The [Cl−], [Ca2+], and [DOC] were adjusted by the addition of NaCl, CaNO3, or humic acid, respectively. On the basis of total silver, increasing [Cl−] over a range of 50 μM to 1,500 μM resulted in a 4.3‐fold increase in the 96‐h LC50 values (decrease in toxicity) for rainbow trout, but did not significantly affect the 96‐h LC50 values for fathead minnows. Increasing water [Ca2+] (from 50 to 2,000 μM) had only a small influence (1.5‐fold increase) on the 96‐h LC50 values in either species. However, increasing DOC levels (from 0.3 to 5.8 mg DOC/L) significantly increased the 96‐h LC50 values (2.7‐ to 4.1‐fold increases) in both species. If the 96‐h LC50 values are calculated on the basis of ionic silver, Ag+ (utilizing the aquatic geochemical computer program MINEQL+ ), then, in the case of rainbow trout, toxicity correlates to Ag+. However, this correlation does not exist for fathead minnows. Increasing [Cl− did not affect the degree of perturbation of Na+ influx during acute exposure (first 4 h) to 8 μg Ag/L in either species, nor did it affect the whole‐body silver uptake rates, but it did reduce the gill silver load. These results demonstrate that differences exist in the way in which water chemistry ameliorates silver toxicity between rainbow trout and fathead minnows.