Formation Of Silver Nanostructures Research Articles

Effect of blue light irradiation on the formation of silver nanostructures in polyvinyl alcohol nanocomposite films

Effect of blue light irradiation on the formation of silver nanostructures in polyvinyl alcohol nanocomposite films

One-Step, On-Site Chemical Printing of a 3D Plasmon-Coupled Silver Nanocoral Substrate toward SERS-Based POCT

Surface-enhanced Raman scattering (SERS) with the advantages of high sensitivity, nondestructive analysis, and a unique fingerprint effect shows great potential in point-of-care testing (POCT). However, SERS faces challenges in rapidly constructing a substrate with high repeatability, homogeneity, and sensitivity, which are the key factors that restrict its practical applications. In this study, we propose a one-step chemical printing strategy for synthesizing a three-dimensional (3D) plasmon-coupled silver nanocoral (AgNC) substrate (only need about 5 min) without any pretreatments and complex instruments. The galvanic replacement between AgNO3 and Cu sheets will provide both Ag0 for the formation of silver nanostructures and Cu2+ for the polymerization of fish sperm DNA (FSDNA). The protection of AgNCs is facilitated by the crosslinked FSDNA, which can improve the stability of the substrate and promote the control of its coral-like morphology. The obtained substrate displays excellent capacity of signal enhancement due to the 3D plasmon coupling both between nanocoral tentacles and between nanocorals and Cu sheets as well. Therefore, the AgNC substrates display high activity (enhancement factor = 1.96 × 108) and uniformity (RSD < 6%). Food colorants have been widely used in various foods to improve their color, but the inevitable toxicity of colorants seriously threatens food safety. Therefore, the proposed AgNC substrates were used to directly quantify three kinds of weak-affinity food colorant molecules including Brilliant Blue, Allura Red, and Sunset Yellow assisted by the capture by cysteamine hydrochloride (CA), showing the detection limits (S/N = 3) of 0.053, 0.087, and 0.089 ppm, respectively. The SERS method has been further applied in the detection of the three kinds of food colorants in both complex food samples and urine with recoveries of 91-119%. The satisfactory detection results suggest that the facile preparation strategy of AgNC substrates will be widely used in SERS-based POCT to promote the development of food safety and on-site healthcare.

Growth mechanism study of silver nanostructures in a limited volume

Recently, high attention has been paid to template synthesis as a method for obtaining nanostructures with predetermined shapes and sizes. This is an obvious approach, in which the size and shape of the pores limit the geometry of the nanostructures formed inside them. As a result, nanostructures completely repeat the shape of the template pores. However, in some cases, the morphology of the resulting structures may differ from the shape of the template, and often these differences are not explained. This is a gap in fundamental knowledge on the mechanism of nanostructure growth in a limited template pore volume. In this work, we partially solve this problem. Using silver as an example, it is shown that by changing only the pore volume, without changing other chemical kinetic conditions, it is possible to controllably create nanostructures with complex geometry. Possible morphologies of nanostructures, such as crystallites, dendrites and “sunflower-like" structures, formed at critical pore diameters, have been identified. The main points inherent to the formation of silver nanostructures in the pores of the SiO2/Si template using the electroless galvanic displacement method were highlighted. The growth mechanism of silver nanostructures in a limited pore volume has been studied and discussed in details.

Visible light promoted porphyrin-based metal-organic adduct

Supramolecular adducts formed by a commercial porphyrin derivative and silver nanoparticles have been obtained using exclusively light as an external trigger that is able to promote the formation of the plasmonic nanostructures. In particular, a water-soluble porphyrin, i.e. tetrakis(4-carboxyphenyl)porphyrin, has been used. It has been thoroughly characterized by means of UV-vis and fluorescence spectroscopy in order to explain its peculiar behavior when illumined with visible photons. Herein we demonstrate that, by means of light illumination, it is possible to tune the porphyrin aggregation state. Furthermore, when the monomeric form of the organic macrocycle is induced and a controlled amount of AgNO[Formula: see text] is simultaneously dissolved, it is possible to promote the formation of silver nanostructures using visible light. The proposed approach allowed porphyrin derivatives/Ag nanoparticles hybrid nanostructures to be obtained without using a chemical reducing agent: the porphyrin derivative simultaneously acts as reducing agent when irradiated by visible light and as a capping agent for the silver nanostructures. The organic/inorganic adduct was characterized by means of steady-state fluorescence that highlights a strong energetic or electronic communication between the two species. XRD and SEM investigations evidence that silver nanoparticles are formed without using any reducing agent.

Silica nanocomposites based on silver nanoparticles-functionalization and pH effect

Current reports in the field of nanotechnology indicate that the properties of metal nanoparticles are determined by their features such as size, shape, composition as well as a degree of crystallinity and stability. These, in turn, may depend heavily on their preparation way, treatment during and after synthesis and finally on properties of the supports and matrices. The goal of presented work was to determine the shape, size, and distribution of silver nanoparticles depending on preparation conditions. In particular, the issues of the formation of silver nanostructures (AgNP) with various shapes and sizes depending on functionalized silica surface as well as on the conditions of the impregnation step by noble metal ions (especially pH) were considered. In particular, the comprehensive approach to determine the impact of pH conditions on the properties of metallic nanoparticles is laid down in this work. Three types of fumed silica materials were selected as the supports of silver nanostructures (Aerosil 150, Aerosil 300 and Silochrom C-120). Silica materials were chemically functionalized by thiol and amine groups and treated with diamminesilver(I) ions [Ag(NH3)2]+. As a result of their reduction silicas adorned with silver nanostructures were obtained. In this work, the AgNP in the form of very small nanoparticles, longitudinal and spherical forms and greater structures with nondescript shape were successfully received and characterized through changing the form of functional groups on the solid surface by adjusting the pH conditions. It turns out that protonation and deprotonation of thiol, amino, and hydroxyl groups can be responsible for possible interactions between noble metal ions and functional groups in the form of both attractive and repulsive electrostatic interactions. The Ag nanoparticle/silica nanocomposites were investigated by X-ray diffraction, atomic force microscopy, potentiometric titration and X-ray photoelectron spectroscopy.

Against to What Observed Up to Now, Formation of Silver Nanostructures with Appropriate Morphologies from Silver Coordination Polymer Precursors by Calcination Rather than Thermal Decomposition in Oleic Acid

In order to studies the effects of various samples of [Ag2(pta)(H2O)]n (1), [H2pta = phthalic acid] coordination polymer, as new precursors with different morphologies, calcination and thermal decomposing in oleic acid of six samples, which were synthesized previously, were carried out. The obtained radiuses were characterized by X-ray powder diffraction and scanning electron microscopy. Silver nanoparticles, microparticles, microporous spongy structure, thin microporous film, mixture of nanosheets and nanoparticles and agglomerated structures of them were obtained during these processes. For about half of the samples, we observed that calcination is more effective than thermal decomposition in oleic acid.

Silver nanostructures evolution in porous SiO2/p-Si matrices for wide wavelength surface-enhanced Raman scattering applications

Abstract

Formation of nanoparticles from thin silver films irradiated by laser pulses in air

Some specific features of the transport of silver nanoparticles onto a SiO2 substrate under focused nanosecond IR laser pulses is experimentally investigated. A possibility of obtaining silver coatings is demonstrated. The formation of silver nanostructures as a result of pulsed laser ablation in air is studied. Nanoparticles are formed by exposing a silver film to radiation of an HTF MARK (Bulat) laser marker (λ = 1064 nm). The thus prepared nanoparticles are analysed using scanning electron microscopy and optical spectroscopy.

Synthesis and characterization of Ag-Protoporphyrin nano structures using mixed co-polymer method

In this paper, we report the synthesis of hybrid silver nanostructures (AgNPs) based on an effective mixing of polyols with Polyvinylpyrrolidone (PVP) and Porphyrin molecules, in particular Protoporphyrin IX (PP). The combination of PVP and PP, which act as co-directing agents and favour the anisotropic growth of nanostructures, yields to very stable complexes for six months. The resulting hybrid silver nanoparticles have been further characterized by polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS), UV–Visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), revealing that the main role of Porphyrin molecules in the formation of silver nanostructures.

Assessing Photocatalytic Activity at the Nanoscale Using Integrated Optical and Electron Microscopy

An integrated optical‐electron microscope is presented that enables the in situ study of dynamic processes on photoactive materials. Here, the deposition of metallic silver nanostructures at ZnO photocatalyst particles is monitored in real time under ambient conditions by means of scanning electron microscopy. Zinc oxide crystals are immobilized on an electron transparent silicon nitride window. By passing UV light through an opposing optically transparent window, the zinc oxide is illuminated resulting in the photocatalytic formation of silver nanostructures. Both windows are part of a specially designed liquid cell filled with a dilute aqueous silver nitrate solution. Using the presented system, different electron detectors are evaluated for their ability to provide detailed images despite the interference caused by the liquid surrounding the sample. Special care has to be taken since direct silver reduction from solution induced by the electron beam interferes with the photocatalytic process. Oxygen gas, produced during the photocatalytic reaction, is also shown to complicate the imaging of the dynamic nanoscale processes in the scanning electron microscope. Nevertheless, the integrated approach allows to directly establish structure–activity relationships and to unravel optically induced processes at nanostructured materials.

The effect of thermolysis temperatures of two silver(I) supramolecular polymers on the formation of silver nanostructures

Two silver(I) supramolecular polymers, [Ag(8-HqH)(8-Hq)] n (1) and {[Ag(8-HqH)2]NO3} n (2), (8-HqH = 8-hydroxyquinoline), have been synthesized and characterized by X-ray powder diffraction, IR, 1H-NMR and 13C-NMR spectroscopies. These supramolecular polymers were used as new precursors for preparation of silver nanostructures. The effect of thermolysis temperature on preparation of silver nanoparticles from these precursors was investigated. The morphology of silver nanostructure is strongly dependent on thermolysis temperature. With increase in temperature, the tendency of silver nanoparticles to agglomerate was increased.

Formation of Silver Nanostructures by Rolling Circle Amplification Using Boranephosphonate-Modified Nucleotides.

We investigate the efficiency of incorporation of boranephosphonate-modified nucleotides by phi29 DNA polymerase and present a simple method for forming large defined silver nanostructures by rolling circle amplification (RCA) using boranephosphonate internucleotide linkages. RCA is a linear DNA amplification technique that can use specifically circularized DNA probes for detection of target nucleic acids and proteins. The resulting product is a collapsed single-stranded DNA molecule with tandem repeats of the DNA probe. By substituting each of the natural nucleotides with the corresponding 5'-(α-P-borano)deoxynucleosidetriphosphate, only a small reduction in amplification rate is observed. Also, by substituting all four natural nucleotides, it is possible to enzymatically synthesize a micrometer-sized, single-stranded DNA molecule with only boranephosphonate internucleotide linkages. Well-defined silver particles are then readily formed along the rolling circle product.

Consecutive Large-Scale Fabrication of Surface-Silvered Polyimide Fibers via an Integrated Direct Ion-Exchange Self-Metallization Strategy

Herein, we report our success on the large-scale online preparation of surface-silver-metallized polyimide (PI) fibers by utilizing silver ammonia complex cation ([Ag(NH3)2](+)) as the silver (Ag) precursor and pyromellitic dianhydride/4,4'-oxidianiline (PMDA/4,4'-ODA)-based polyimide as the matrix via a direct ion-exchange self-metallization process integrated within a consecutive fiber-spinning procedure. The method works by using the online freshly prepared PMDA/4,4'-ODA-based poly(amic acid) (PAA) fibers as the starting material to perform an ion-exchange reaction in aqueous silver(I) solution to load silver(I) into the PAA precursor fibers, followed by a programmed stepwise thermal treatment process to convert PAA to its final imide form with the concomitant silver(I) reduction and the subsequent aggregation, producing the surface-silvered polyimide hybrid fibers. The influence of thermal cycles on the formation of silver nanostructures, and the variation of surface morphologies and fiber properties during the heating process were investigated. Experimental results indicate that the PI-Ag fibers were produced with good mechanical and thermal properties. In addition, bioassessment suggests that the hybrid fibers exhibit superior antibacterial activities (99.99% in 24 h toward E. coli ). Outstanding electrical conductive properties of a certain length of the PI-Ag hybrid fiber (electrical resistance: ca. 0.1 Ω cm(-1)) could also be realized on the composite fibers but with severe destructions in the final mechanical properties. The fibers were also characterized by FTIR, ICP, XRD, SEM, and TEM.

Studies of the interaction of two organophosphonates with nanostructured silver surfaces

Electrochemical cycling of silver surfaces in the presence of the organophosphonates paraoxon and malathion leads to changes in the electrochemical response of silver and the formation of silver nanostructures. Adsorption of the organophosphonates onto the silver surfaces causes a significant reduction in the observed current response due to an increase in the charge transfer resistance. Surface enhanced Raman spectroscopy (SERS) measurements indicate that paraoxon adsorbs with no structural changes, while malathion decomposes and a thiophosphonate interacts with the surface. The SERS study of these adsorbates was carried out by changing the electrochemical conditions and the concentration of the organophosphonates. The size of the nanostructures greatly influences the SERS signal and it is observed that the strongest enhancement is observed for mid-sized nanostructures with a uniform thickness on the surface. The limit of detection was shown to be in the range of 10 nM to 10 pM for paraoxon and malathion, respectively.

In situ formation of silvernanostructures within a polysaccharide film and application as a potential biocompatible fluorescence sensing medium

Simple to manufacture polysaccharide films containing a silver salt, from which silver nanostructures can be produced in situ by light irradiation, were investigated for possible biosensing applications. The silver nanostructures were patterned in situ within a film and cast from a liquid solution of gellan gum, using a compact time-resolved fluorescence microscope. The position and time of irradiation, made using a semiconductor laser in CW mode, were computer controlled. Evidence for their formation was obtained via UV-vis spectroscopy, AFM and SEM-EDAX. On drying the polysaccharide film exhibited a viscosity increase of several orders of magnitude, which was elucidated by changes in the fluorescence lifetime of a probe molecule (DASPMI). To demonstrate the potential for biocompatible sensing applications the influence of the presence of areas of silver nanostructures on the fluorescence of a protein (bovine serum albumin) labelled with fluorescein isothiocyanate was monitored via fluorescence lifetime imaging and the photophysical behaviour found to be consistent with a metal induced increase in the radiative decay rate.

The influence of surface composition of Ag 3PW 12O 40 and Ag 3PMo 12O 40 salts on their catalytic activity in dehydration of ethanol

The aim of this work was to investigate the influence of relative humidity of air on the catalytic activity of Ag 3PW 12O 40 and Ag 3PMo 12O 40 salts in the vapor-phase dehydration of ethanol. The reaction was performed in air of relative humidity of 2% or 9% and in the temperature range of 373–493 K. The catalytic activity of Ag 3PW 12O 40 salt was much higher than the one obtained for Ag 3PMo 12O 40 salt and strongly dependent on relative humidity of air. The XRD measurements showed that the structure of Ag 3PW 12O 40 salt loses the water hydrating silver in the range of 473–573 K whereas Ag 3PMo 12O 40 salt in 373–473 K. The FT-IR spectra demonstrated the stability of Keggin structure of Ag 3PW 12O 40 salt after reaction, independently of relative humidity of air. However, the XPS spectroscopy exhibited the changes in surface composition of this salt after reaction in air of 2% of relative humidity whereas the SEM imaging displayed the formation of silver nanostructures on its surface. The Ag 3PW 12O 40 salt remained stable after reaction in air of 9% of relative humidity. In case of Ag 3PMo 12O 40 salt analyzed before and after ethanol dehydration, a very limited difference in surface composition was found by XPS that was supported by SEM imaging.

Silver nanoparticles with gelatin nanoshells: photochemical facile green synthesis and their antimicrobial activity

In the current study, a facile green synthesis of silver-gelatin core–shell nanostructures (spherical, spherical/cubic hybrid, and cubic, DLS diameter: 4.1–6.9 nm) is reported via the wet chemical synthesis procedure. Sunlight-UV as an available reducing agent cause mild reduction of silver ions into the silver nanoparticles (Ag-NPs). Gelatin protein, as an effective capping/shaping agent, was used in the reaction to self-assemble silver nanostructures. The formation of silver nanostructures and their self-assembly pattern was confirmed by SEM, AFM, and TEM techniques. Further investigations were carried out using zeta-potential, UV–Vis, FTIR, GPC, and TGA/DTG/DTA data. The prepared Ag-NPs showed proper and acceptable antimicrobial activity against three classes of microorganisms (Escherichia coli Gram-negative bacteria, Staphylococcus aureus Gram-positive bacteria, and Candida albicans fungus). The antibacterial and antifungal Ag-NPs exhibit good stability in solution and can be considered as promising candidates for a wide range of biomedical applications.

Temperature controlled synthesis of silver nanostructures of variable morphologies in aqueous methyl cellulose matrix

Spherical, hexagonal, triangular and bar shaped silver nanostructures have been synthesized at large scale in aqueous media using methyl cellulose (MC) as soft template. Synthesis is based on the reduction of Ag + by hydrogen at different temperatures. Morphology of particles is mostly spherical at 60 °C with an average diameter 4–8 nm, whereas hexagonal, triangular and truncated hexagon silver nanostructures are obtained at 80 °C. On the other hand bar shaped silver nanoparticles are formed as the reaction is carried out at 90 °C. Silver nanoparticles are characterized using UV–Vis and TEM study. Formation of silver nanostructures of variable morphologies has been explained in terms of different shaped template formed by MC at different temperature due to its thermogelation properties.

In situ formation of silver nanostructures produced via laser irradiation within sol–gel derived films and their interaction with a fluorescence tagged protein

The presence of a conducting metal surface is known to affect the emission of a fluorophore in its proximity. This can lead to an enhancement in its fluorescence intensity along with a decrease in the fluorescence lifetime. This phenomenon, sometimes known as metal enhanced fluorescence, has implications in the area of sensing and "lab on a chip" applications. Here controlled, localised use of metallic structures can be advantageous in enhancing the detection of a fluorescent signal. The sol-gel technique has been demonstrated as a useful method by which to produce a biocompatible material. The versatility of the reaction allows for the inclusion of metal ions, which can form metallic nanostructures permitting the potential enhancement of fluorescence to be exhibited. In this work we incorporate silver nitrate within silica sol-gel derived films produced using a simple procedure at relative low temperatures (close to ambient). A compact time-resolved fluorescence microscope equipped with a semiconductor laser was used to photoactivate the silver ions to form localised metallic structures within the films. Patterning was achieved by computer control of the microscope stage and using the laser in CW mode. The films were characterised using AFM and UV-vis spectroscopy to ascertain the presence of the photoactivated silver nanostructures. The effect of the presence of these structures was elucidated by studying the time-resolved fluorescence of FITC labelled bovine serum albumin adsorbed to the films, where a decrease in the lifetime of the FITC label was observed in the location of the nanostructures.

Synthesis of silver nanowires via electroplating technology and its surface enhanced Raman scattering effect

This very paper is focusing on the preparation of silver nanostructures and the surface enhanced Raman scattering effect of the silver nanostructures produced. Via electroplating technology, silver nanowires and nanoparticles were prepared on silicon wafers. Characterization was performed by X-ray diffraction, scanning electron microscope, transmission electron microscope equipped with X-ray energy dispersion spectroscope and selected area electron diffraction, which reveals that the formation of silver nanostructures depends on the over-potential. The produced silver nanowires are of crystalline FCC structure and grow in 〈0 1 1〉 direction. The growth mechanism has been further discussed. The surface enhanced Raman scattering effect is achieved with the silver nanostructures produced.