Silver Coatings Research Articles

Fiber optic SPR nanosensor based on synergistic effects of CNT/Cu-nanoparticles composite for ultratrace sensing of nitrate

A fiber optic SPR (FOSPR) based probe with coatings of silver and nanocomposite of CNT/Cu-nanoparticles over unclad core of the fiber is proposed for the sensing of nitrate. The sensing is based on the reduction of nitrate on interaction with copper nanoparticles and the formation of ammonium ions. The adsorption of ammonium ions on CNTs changes the dielectric properties of CNT/Cu-NPs nanocomposite which is measured as the shift in resonance wavelength. The composition ratio and the thickness of the CNT/Cu-NPs nanocomposite layer along with the pH of the nitrate solution are optimised for the best performance of the sensor. The probe operates for the concentration range of 10−6M–5×10−3M and offers a high sensitivity of 80.62×106nm/M. Due to the operation in this wide range, the probe paves the way for a novel means to detect nitrate in real samples and highlights the feasibility of CNT/Cu-NPs nanocomposite based SPR sensors. Moreover, the sensor possesses 4nM as the limit of detection. This is the lowest value reported in the literature. The entire sensing procedure could be completed within 30s with only 20ml of analyte that are the main demands of effective and fast detection in real sample.

A Novel Silver Coating for Antigen-Microarray Preparation Suitable for Application on Antibody Recognition

The present paper reports the development of a novel silver nanoparticles-derivatized polystyrene substrate useful for for protein microarray application. The silvered coating was prepared by a novel photochemical method. Various coatings were tested and characterized by means of chemical-physical methods. It was demonstrated that these methods are useful for the preparation of protein microarray for the analysis of human antibody by sandwich methods of fluorescence immunoassay (Alexa labeled). Comparative studies were carried out with different printing buffers and various surface derivatization to find the optimal conditions for antigen immobilization. Therein described assay, the human myeloperoxidase antigen (MPO) was quantitative detected directly from human serum. The cross-reactivity was here evaluated by reaction with recombinant human tissue transglutaminase antigen (htTG), a linearity response from 20 to 2000 ng/μl was investigated by human IgG probes. The data indicate an increase of both signal-to-noise ratio value and reproducibility for the silver nanoparticle coating respect the value obtained for the polystyrene commercial slides.

Effect of ultrasound on silver electrodeposition: Crystalline structure modification

An attractive possibility for influencing microstructures of electrodeposited coatings, and therefore their properties such as hardness, brightness etc. resides in the use of ultrasound. This method is particularly competitive as it may result in a reduction of chemical use, or even in the complete suppression of chemicals. This paper deals with silver coatings depending strongly on current density, with two main categories identified by X-ray diffraction: one poorly structured and the other following the [110] orientation. It is interesting to note that, while changing from still to mechanically stirred conditions, the value of the current density threshold moves from 2.5mAcm−2 to 5mAcm−2. When ultrasound is used (575kHz or 20kHz), this coating microstructure modification threshold occurs at higher current density values when coatings are produced under sonication, while agitation is kept constant. In both cases, the shift is about 15mAcm−2. It is noteworthy that silver electrodeposits elaborated under 20kHz ultrasound conditions appear to be less oriented than those obtained under high frequency conditions.

Simultaneous tuning of electric field intensity and structural properties of ZnO: Graphene nanostructures for FOSPR based nicotine sensor

We report theoretical and experimental realization of a SPR based fiber optic nicotine sensor having coatings of silver and graphene doped ZnO nanostructure onto the unclad core of the optical fiber. The volume fraction (f) of graphene in ZnO was optimized using simulation of electric field intensity. Four types of graphene doped ZnO nanostructures viz. nanocomposites, nanoflowers, nanotubes and nanofibers were prepared using optimized value of f. The morphology, photoluminescence (PL) spectra and UV–vis spectra of these nanostructures were studied. The peak PL intensity was found to be highest for ZnO: graphene nanofibers. The optimized value of f in ZnO: graphene nanofiber was reconfirmed using UV–vis spectroscopy. The experiments were performed on the fiber optic probe fabricated with Ag/ZnO: graphene layer and optimized parameters for in-situ detection of nicotine. The interaction of nicotine with ZnO: graphene nanostructures alters the dielectric function of ZnO: graphene nanostructure which is manifested in terms of shift in resonance wavelength. From the sensing signal, the performance parameters were measured including sensitivity, limit of detection (LOD), limit of quantification (LOQ), stability, repeatability and selectivity. The real sample prepared using cigarette tobacco leaves and analyzed using the fabricated sensor makes it suitable for practical applications. The achieved values of LOD and LOQ are found to be unrivalled in comparison to the reported ones. The sensor possesses additional advantages such as, immunity to electromagnetic interference, low cost, capability of online monitoring, remote sensing.

Roman sophisticated surface modification methods to manufacture silver counterfeited coins

By means of the combined use of X-ray photoelectron spectroscopy (XPS), optical microscopy (OM) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) the surface and subsurface chemical and metallurgical features of silver counterfeited Roman Republican coins are investigated to decipher some aspects of the manufacturing methods and to evaluate the technological ability of the Roman metallurgists to produce thin silver coatings. The results demonstrate that over 2000 ago important advances in the technology of thin layer deposition on metal substrates were attained by Romans. The ancient metallurgists produced counterfeited coins by combining sophisticated micro-plating methods and tailored surface chemical modification based on the mercury-silvering process. The results reveal that Romans were able systematically to chemically and metallurgically manipulate alloys at a micro scale to produce adherent precious metal layers with a uniform thickness up to few micrometers. The results converge to reveal that the production of forgeries was aimed firstly to save expensive metals as much as possible allowing profitable large-scale production at a lower cost. The driving forces could have been a lack of precious metals, an unexpected need to circulate coins for trade and/or a combinations of social, political and economic factors that requested a change in money supply. Finally, some information on corrosion products have been achieved useful to select materials and methods for the conservation of these important witnesses of technology and economy.

Highly efficient and selective leaching of silver from electronic scrap in the base-activated persulfate – ammonia system

A system composed of persulfate salt and ammonia in highly alkaline aqueous solution is developed and examined for leaching metallic silver from elements of the electronic waste materials (e-scrap). Strong base activates persulfate ions providing in situ generation of highly reactive oxygen molecules. The oxidized metal forms then well soluble complex ions with ammonia ligands. The kinetic studies of the leaching process were performed for pure metallic silver. They revealed that the efficiency of the process is affected by the type of the persulfate salt. By employing potassium persulfate one obtains significantly (more than 50% for silver plates and more than 100% for silver powder) increased efficiency of silver dissolution compared to the solution composed of either sodium or ammonium persulfates. In the range of persulfate concentrations between 0.02 and 0.23mol/L the apparent reaction order with respect to the persulfate concentration was similar for all persulfate salts and was estimated to be around 0.5. The room temperature (22±2°C) seems to be an optimal temperature for the leaching process. An increase in the temperature resulted in the significant drop in the silver dissolution rate due to the decreased solubility of oxygen. Based on these results a possible mechanism of dissolving silver is discussed and the optimal composition of the leaching solution is formulated. The obtained formulation of the leaching solution was applied for the extraction of silver coatings of Cu-based e-waste scrap and the obtained results revealed an important effect of copper in the mechanism of the leaching process. The regression analysis of the leaching curve indicated that each gram of base-activated potassium persulfate under the specified conditions may leach almost 100mg of silver coatings in a form of well soluble diamminesilver (I) complex. The silver complex can be relatively easy reduced to metallic silver. The method developed is relatively cheap, low toxic and does not produce harmful by-products.

Identifying Key Factors towards Highly Reflective Silver Coatings

This paper attempts to identify key factor(s) for highly reflective silver (Ag) coatings. Investigation was made over the crystal orientation and surface roughness, using several types of surfaces, including electroplated Ag polycrystal films, physical vapour deposited polycrystal Ag films, and single crystal Ag foils with different crystal orientations. In each type of the surfaces, surface roughness was varied so that, for different combinations of crystal orientation, roughness would elucidate the key factors towards highly reflective Ag coatings. It is found that surface roughness plays a critical role in determining the reflectance, while the crystal orientation has negligible effect. The mean reflectance and one-way ANOVA analysis indicate that the single crystal Ag foils with three orientations performed statistically the same in the same roughness group at significance levelα= 0.05. Moreover, correlation between the surface reflectance and surface roughness has been proposed for the benefit of coating design. Refection data obtained from the polycrystalline silver samples are used to verify the accuracy of the proposed correlations. It was observed that the development surface area ratio,Sdr, is a better roughness indicator in predicting the reflectance of polycrystalline silver films than the arithmetic average roughness,Ra.

Conductive silver coatings with ultra-low silver consumption on polyimide film via a mild surface ion exchange self-metallization method

Conductive silver coating with ultra-low silver consumption on polyimide filmviaa mild surface ion exchange self-metallization method.

Deposition of metallic silver coatings by Aerosol Assisted MOCVD using two new silver β-diketonate adduct metalorganic precursors.

This work reports two new silver metalorganic precursors for the chemical vapor deposition of Ag metallic coatings. Both precursors are based on β-diketonate adducts, namely, Ag(hfac)(L) (H-hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), where L is 1,10-phenanthroline (phen) or 2,5,8,11-tetraoxadodecane (triglyme). Using these ligands, the designed precursors have better solubility in alcoholic solvents and are less toxic and costly than previously reported ones. The new precursors have been characterized and their crystallographic structure solved. With the new triglyme precursor, [Ag(triglyme)2]+[Ag(hfac)2]-, pure metallic Ag coatings made of Ag nanoparticles about 20 nm in diameter were succesfully deposited on glass and Si substrates using Aerosol Assisted Metalorganic CVD (AA-CVD).

Highly sensitive and selective erythromycin nanosensor employing fiber optic SPR/ERY imprinted nanostructure: Application in milk and honey

An erythromycin (ERY) detection method is proposed using the fiber optic core decorated with the coatings of silver and an over layer of ERY imprinted nanoparticles. Synthesis of ERY imprinted nanoparticles is carried out using miniemulsion method. The operating range of the sensor is observed to be from 1.62×10−3 to 100µM while the sensor possesses the linear response for ERY concentration range from 0.1 to 5µM. The sensing method shows a maximum sensitivity of 205nm/µM near ERY concentration of 0.01µM. The detection limit and the quantification limit of the sensor are found to be 1.62×10−3µM and 6.14×10−3µM, respectively. The sensor’s applicability in real samples is also examined and is found to be in good agreement for the industrial application. The sensor possesses numerous advantages like fast response time (<15s), simple, low cost, highly selective along with abilities towards online monitoring and remote sensing of analyte.

Fiber Optic SPR-Based Uric Acid Biosensor Using Uricase Entrapped Polyacrylamide Gel

In this letter, we report a fiber optic biosensor based on surface plasmon resonance (SPR) for the detection of uric acid in aqueous samples. The sensing probe is prepared by successive coatings of silver and silicon layers over a small unclad length of the plastic clad silica optical fiber in the middle. Thereafter, the probe is dipped in a polyacrylamide gel containing enzyme uricase to immobilize it using a gel entrapment method. The sensor is characterized using a wavelength interrogation method. The SPR spectra corresponding to different concentrations of uric acid in the range of 0-0.9 mM are recorded. A red shift in the resonance wavelength is observed with an increase in the concentration of uric acid around the probe. In addition, the sensitivity of the proposed biosensor is studied in relation to parameters, such as concentration and pH of the uric acid solution. Finally, the sensor is highly selective and possesses better limit of detection and limit of quantification.

Heterogeneous nucleation and surface conformal growth of silver nanocoatings on colloidal silica in a continuous flow static T-mixer

Abstract Dielectric-metal core-shell particles with morphologically tunable optical properties are highly promising candidates for applications ranging from theranostics, energy harvesting and storage to pigments and sensors. Most structures of interest have, until now, been produced in small volume wet chemical batch approaches which are difficult to scale. In extension to the growing interest in continuous flow process for the scalable synthesis of single phase nanomaterials, here we describe the formation of two-phase core-shell particles. Specifically, the coating of silver onto colloidal silica particles using a static T-mixer approach is presented. The coating is achieved in a single reaction step in which careful control of educt concentration and process conditions leads to nucleation and surface conformal growth of silver. Through two generations of reactor, good coating yield and process reproducibility are demonstrated. In particular, the ability to control the characteristic time of mixing, as verified by the Villermaux-Dushmann reaction, was shown to be crucial in narrowing the range of morphologies obtained in the product particles. Moreover we could tune, through process parameters, the degree of coating of the core particles, leading to patchy particles, Janus particles and even complete nanoshells. Since silver nanostructures have a strong structure-dependent plasmon resonance, we could verify the coating morphologies via optical spectroscopy and electrodynamic simulations. Optical measurements were also used in order to optimize, via trial and error, the continuous flow process parameters to produce a high coating yield. This opens up future potential for feedback-driven optimization of particle coating. Finally, we demonstrate that the silver coatings can be morphologically stabilized, opening up the possibility of effective formulation for applications.

Properties of oxide films on nickel contact surfaces

The possibilities of changing the conductivity of surface films during electrolysis are studied. The results of experimental research into films on nickel contacts are presented. From a comparison of ellipsometric, X-ray diffraction, and Auger-spectrum measurements of nickel coating surfaces obtained from electrolytes with organic components, it is revealed that the structure and composition of the surface films undergo changes which result in a decrease in the contact resistance. This makes it possible to employ such films in low-current contacts instead of silver or silver-alloy coatings.

Effect of Silver or Copper Nanoparticles-Dispersed Silane Coatings on Biofilm Formation in Cooling Water Systems.

Biofouling often occurs in cooling water systems, resulting in the reduction of heat exchange efficiency and corrosion of the cooling pipes, which raises the running costs. Therefore, controlling biofouling is very important. To regulate biofouling, we focus on the formation of biofilm, which is the early step of biofouling. In this study, we investigated whether silver or copper nanoparticles-dispersed silane coatings inhibited biofilm formation in cooling systems. We developed a closed laboratory biofilm reactor as a model of a cooling pipe and used seawater as a model for cooling water. Silver or copper nanoparticles-dispersed silane coating (Ag coating and Cu coating) coupons were soaked in seawater, and the seawater was circulated in the laboratory biofilm reactor for several days to create biofilms. Three-dimensional images of the surface showed that sea-island-like structures were formed on silane coatings and low concentration Cu coating, whereas nothing was formed on high concentration Cu coatings and low concentration Ag coating. The sea-island-like structures were analyzed by Raman spectroscopy to estimate the components of the biofilm. We found that both the Cu coating and Ag coating were effective methods to inhibit biofilm formation in cooling pipes.

Efficacy of silver coated surgical sutures on bacterial contamination, cellular response and wound healing

The resistance demonstrated by many microorganisms towards conventional antibiotics has stimulated the interest in alternative antimicrobial agents and in novel approaches for prevention of infections. Silver, a natural braod-spectrum antimicrobial agent known since antiquity, has been widely employed in biomedical field due to its recognized antibacterial, antifungal and antiviral properties. In this work, antibacterial silver coatings were deposited on absorbable surgical sutures through the in situ photo-chemical deposition of silver clusters. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and thermo-gravimetric analysis (TGA) were performed in order to investigate the presence and distribution of the silver clusters on the substrate. The amounts of silver deposited and released by the silver treated sutures were calculated through Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS), and the results were related to the biodegradation of the material. The microbiological properties and the potential cytotoxicity of the silver-treated sutures were investigated in relation with hydrolysis experiments, in order to determine the effect of the degradation on antibacterial properties and biocompatibility.

The potential of photo-deposited silver coatings on Foley catheters to prevent urinary tract infections

Catheter-associated urinary tract infection (CAUTI) represents one of the most common causes of morbidity and mortality. The resistance demonstrated by many microorganisms to conventional antibiotic therapies and the increasing health-care costs have recently encouraged the definition of alternative preventive strategies, which can have a positive effect in the management of infections. Antimicrobial urinary catheters have been developed through the photo-chemical deposition of silver coatings on the external and luminal surfaces. The substrates are exposed to ultraviolet radiation after impregnation into a silver-based solution, thus inducing the in situ synthesis of silver particles. The effect of the surface treatment on the material was investigated through scanning electron microscopy (SEM) and silver ion release measurements. The ability of microorganisms commonly associated with urinary tract infections was investigated in terms of bacterial viability, proliferation and biofilm development, using Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis as target organisms. The silver coatings demonstrated good distribution of silver particles to the substrate, and proved an effective antibacterial capability in simulated biological conditions. The low values of silver ion release demonstrated the optimum adhesion of the coating. The results indicated a good potential of silver-based antimicrobial materials for prevention of catheter-associated urinary tract infection.

Silver-coated glass fabric composites prepared by electroless plating

Silver-coated glass fabrics have been successfully obtained by a facile and versatile electroless plating method, and the silver layers on the surface of glass fabrics were compact and uniform. The purity and quality of these silver coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that the quality of the coating layer was influenced by the dosage of reducing agent and reaction time. The composites possessed an excellent conductivity, and the optimal volume resistivity could reach 6.54×10−4Ωcm. It was expected that such conductive composites have extensive application in shielding materials.

In Vitro Assessment of the Antibacterial Potential of Silver Nano-Coatings on Cotton Gauzes for Prevention of Wound Infections.

Multidrug-resistant organisms are increasingly implicated in acute and chronic wound infections, thus compromising the chance of therapeutic options. The resistance to conventional antibiotics demonstrated by some bacterial strains has encouraged new approaches for the prevention of infections in wounds and burns, among them the use of silver compounds and nanocrystalline silver. Recently, silver wound dressings have become widely accepted in wound healing centers and are commercially available. In this work, novel antibacterial wound dressings have been developed through a silver deposition technology based on the photochemical synthesis of silver nanoparticles. The devices obtained are completely natural and the silver coatings are characterized by an excellent adhesion without the use of any binder. The silver-treated cotton gauzes were characterized through scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA) in order to verify the distribution and the dimension of the silver particles on the cotton fibers. The effectiveness of the silver-treated gauzes in reducing the bacterial growth and biofilm proliferation has been demonstrated through agar diffusion tests, bacterial enumeration test, biofilm quantification tests, fluorescence and SEM microscopy. Moreover, potential cytotoxicity of the silver coating was evaluated through 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide colorimetric assay (MTT) and the extract method on fibroblasts and keratinocytes. Inductively coupled plasma mass spectrometry (ICP-MS) was performed in order to determine the silver release in different media and to relate the results to the biological characterization. All the results obtained were compared with plain gauzes as a negative control, as well as gauzes treated with a higher silver percentage as a positive control.

Contact Resistance and Metallurgical Connections Between Silver Coated Polymer Particles in Isotropic Conductive Adhesives

Recently, there has been an increasing interest in silver thin film coated polymer spheres as conductive fillers in isotropic conductive adhesives (ICAs). Such ICAs yield resistivities similar to conventional silver flake based ICAs while requiring only a fraction of the silver content. In this work, effects of the nanostructure of silver thin films on inter-particle contact resistance were investigated. The electrical resistivity of ICAs with similar particle content was shown to decrease with increasing coating thickness. Scanning electron micrographs of ion milled cross-sections revealed that the silver coatings formed continuous metallurgical connections at the contacts between the filler particles after adhesive curing at 150°C. The electrical resistivity decreased for all samples after environmental treatment for 3 weeks at 85°C/85% relative humidity. It was concluded that after the metallurgical connections formed, the bulk resistance of these ICAs were no longer dominated by the contact resistance, but by the geometry and nanostructure of the silver coatings. A figure of merit (FoM) was defined based on the ratio between bulk silver resistivity and the ICA resistivity, and this showed that although the resistivity was lowest in the ICAs containing the most silver, the volume of silver was more effectively used in the ICAs with intermediate silver contents. This was attributed to a size effect due to smaller grains in the thickest coating.

Tuning the field distribution and fabrication of an Al@ZnO core–shell nanostructure for a SPR-based fiber optic phenyl hydrazine sensor

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor that uses coatings of silver and aluminum (Al)-zinc oxide (ZnO) core–shell nanostructure (Al@ZnO) for the detection of phenyl hydrazine (Ph-Hyd). To optimize the volume fraction (f) of Al in ZnO and the thickness of the core–shell nanostructure layer (d), the electric field intensity along the normal to the multilayer system is simulated using the two-dimensional multilayer matrix method. The Al@ZnO core–shell nanostructure is prepared using the laser ablation technique. Various probes are fabricated with different values of f and an optimized thickness of core–shell nanostructure for the characterization of the Ph-Hyd sensor. The performance of the Ph-Hyd sensor is evaluated in terms of sensitivity. It is found that the Ag/Al@ZnO nanostructure core–shell-coated SPR probe with f = 0.25 and d = 0.040 μm possesses the maximum sensitivity towards Ph-Hyd. These results are in agreement with the simulated ones obtained using electric field intensity. In addition, the performance of the proposed probe is compared with that of probes coated with (i) Al@ZnO nanocomposite, (ii) Al nanoparticles and (iii) ZnO nanoparticles. It is found that the probe coated with an Al@ZnO core–shell nanostructure shows the largest resonance wavelength shift. The detailed mechanism of the sensing (involving chemical reactions) is presented. The sensor also manifests optimum performance at pH 7.