Silver Nanoparticle

We have investigated the spatial self-phase modulation of palm oil containing silver nanoparticles (palm oil/Ag-NPs). The study carried out using continuous wave diode pumped solid state laser with wavelength of 405 nm and power of 50 mW. The strong spatial selfphase modulation patterns were observed that suggest the palm oil/Ag-NPs have a relatively large nonlinear refractive index. The obtained values of nonlinear refractive index were increased with the increase of volume fractions. The observed experimental patterns were also theoretically modeled which are in good agreement with experimental results.

Colloidal silver nanoparticles (Ag-NPs) were successfully prepared using a nanosecond pulsed Nd:YAG laser, l ¼ 1064 nm, with laser fluence of approximately about 360 mJ/pulse, in an aqueous gelatin solution. In this work, gelatin was used as a stabilizer, and the size and optical absorption properties of samples were studied as a function of the laser ablation times. The results from the UVevis spectroscopy demonstrated that the mean diameter of Ag-NPs decrease as the laser ablation time increases. The Ag-NPs have mean diameters ranging from approximately 10 nm to 16 nm. Compared with other preparation methods, this work is clean, rapid, and simple to use. Ó

We successfully prepared colloidal silver nanoparticles (Ag-NPs) using a nanosecond pulsed Nd:YAG laser, = 532 nm, with laser fluence of approximately about 0.6 J/pulse, in an aqueous gelatin solution. The size and optical absorption properties of samples were studied as a function of the laser repetition rates. The results from the UV-vis spectroscopy demonstrated that the mean diameter of Ag-NPs increase with the laser repetition rate increases. The Ag-NPs have mean diameters ranging from approximately 9 nm to 15 nm. Compared with other preparation methods, this work is clean, rapid, and simple to use.

In this study, we report an effective process for preparing silver nanoparticles (Ag NPs) by using Green reduction method of AgNO 3 in interlamellar space of Montmorillonite/Starch Bionanocomposites (MMT/Stc BNCs) suspension with moderate temperature. In here MMT, Starch, ȕ-D-glucose and AgNO 3 were used as a solid support, stabilizer, green reducing agent and silver precursor, respectively. Bionanocomposites material based on MMT, starch and silver nanoparticles (Ag/MMT/Stc BNCs) were prepared by adding starch and silver nitrate respectively into montmorillonite (MMT) dispersions in double distill water solution. The crystalline structure, d-spacing of interlayer of MMT, the size distributions, surface Plasmon resonance and functional groups of synthesized Ag NPs in the MMT/Stc BNCs were characterized using Powder X-Ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), UV-visible spectroscopy and Fourier Transform Infrared Spectroscopy (FT-IR). The results obtained from TEM showed that the Ag NPs prepared in the extra surface of MMT layers have larger than Ag NPs intercalated between MMT layers, the particle size of nanoparticles synthesized by this processes were from 9 to 39 nm. Powder X-Ray Diffraction analysis showed that the synthesized Ag NPs crystallized in face centered cubic (fcc) symmetry. With gentle heating, this system is a mild, renewable, inexpensive, and nontoxic reducing agent. The synthesized bionanocomposites are very stable in aqueous solution over a long period of time (i.e., 3 months) without any sign of precipitation. Silver nanoparticles in MMT/Stc suspension could be suitable to use various medical applications. Since MMT is viewed as ecologically and environmentally inert material and used for biological application such as cosmetics and pharmaceutical usage.

We have successfully developed a simple method for preparing silver nanoparticles (Ag NPs) using UV irradiation of AgNO 3 in the interlamellar space of a montmorillonite (MMT) without any reducing agent or heat treatment. The properties of Ag/MMT nanocomposites were studied as a function of the UV irradiation period. UV irradiation disintegrated the Ag NPs into smaller size until a relatively stable size and size distribution were achieved. The results from UV-vis spectroscopy show that particles size of Ag NPs decrease with the increase of irradiation period. The crystalline structure of Ag NPs was determined by powder X-ray diffraction (PXRD).

Silver nanostructures were prepared by chemical synthesis using polyvinyl alcohol (PVA) and the characteristic surface plasmon absorption of this nano-composite polymer was studied using UV-Vis absorption spectra. Samples were characterized using Scanning Electron Microscope (SEM), Energy Dispersive X-ray diffraction (EDX) and Transmission Electron Microscope (TEM). It is seen that truncated octahedral silver nanoplates has been formed with high intense plasmon absorption and it is the first report of truncated octahedral silver nanoplate using polyvinyl alcohol. It is found that the intensity of plasmon absorption depends not only on the density of the material but also on the shape of the nanostructures formed and also it is found that the weight percentage of silver has a control on deciding the shape of the particles in polyvinyl alcohol (PVA).

Complex light fields, such as speckle patterns, contain many phase vortices. One way of determining a vortex-carrying beam's vortex charge includes interference with another beam. On the other hand, we present a single-beam method for analyzing vortices' wavefronts using surface plasmon polaritons. We use a subwavelength slit in a film to slice up a vortex beam, and measure the diffraction of the generated plasmons by scattering off a second slit. By moving the slits across the beam, we create a tomogram, from which we determine the beam's vortex charge visually. The method can easily be extended to more complex light fields; it is foreseen that it may result in a miniature device.

Chiral imprinting in molecular and polymer films and enantioseparations using chiral substrates are well known phenomena. 1 It has been found that the binding of chiral molecules to a substrate lacking optical rotation has induced optical activity in the substrate. Small metal clusters have been shown to exhibit optical activity depending on their arrangement 2 or growth template. These metallic nanoparticles have usually been grown through the reduction of metallic cations using various templates (e.g., various surfactants and peptides). DNA was found to be an excellent template for the growth of metallic nanoparticles. 3 In this work we demonstrate that a DNA template induces chirality of silver nanoparticles grown in it. The silver particles were produced by reduction of Ag + bound to 700 base pairs poly(dG)poly(dC). The complex between the DNA and Ag + ions is stable and does not dissociate during size-exclusion HPLC. Reduction of Ag + with NaBH 4 in anaerobiosis resulted in the appearance of a new band centered around 425 nm in the absorption and CD spectra of the complex. This band in the CD spectrum is associated with the plasmon of the silver nanoparticles formed on the poly(dG-)-poly(dC) scaffold. In order to understand whether or not the chirality is induced in the particles during its formation in the optically active DNA environment we have prepared silver nanocrystals separately from the DNA and complexed them with the DNA afterwards. Only the silver particles, which were grown on the DNA template, show a characteristic CD spectrum in the 350-550 nm region. Neither Ag nanocrystals in solution nor the nanoparticles absorbed to the DNA (post-synthesis) showed CD response around 400 nm (see . Based on the similarity of the TEM images of the two types of DNA-Ag samples and large difference between the CD spectra of the two samples we suggest that the DNA directed asymmetric assembly of the particles from Ag atoms bound to this chiral template. The Ag nanocrystals produced in optically inactive aqueous environment by reduction of Ag + atoms and further complexation of the particles with the DNA lack this chirality. The passivation of small gold clusters with chiral molecules gives rise to optical activity 4 . Several explanations for this optical activity were thought of, among them the formation of a chiral metal core due to the influence of the chiral ligand

Silver nanoparticles were successfully synthesized from AgNO 3 through a simple green route using the latex of Jatropha curcas as reducing as well as capping agent. Nanoparticles were characterized with the help of HRTEM, X-ray diffraction and UV-vis absorption spectroscopy. X-ray diffraction analysis showed that the nanoparticles were of face centered cubic structure. A comparison of radius of nanoparticles obtained from HRTEM image with the optimized cavity radius of the cyclic peptides present within the latex revealed that the particles having radius 10-20 nm are mostly stabilized by the cyclic peptides.

This review presents an overview of silver nanoparticles (Ag NPs) preparation by green synthesis approaches that have advantages over conventional methods involving chemical agents associated with environmental toxicity. Green synthetic methods include mixed-valence polyoxometallates, polysaccharide, Tollens, irradiation, and biological. The mixed-valence polyoxometallates method was carried out in water, an environmentally-friendly solvent. Solutions of AgNO 3 containing glucose and starch in water gave starchprotected Ag NPs, which could be integrated into medical applications. Tollens process involves the reduction of Ag(NH 3 ) 2 + by saccharides forming Ag NP films with particle sizes from 50-200 nm, Ag hydrosols with particles in the order of 20-50 nm, and Ag colloid particles of different shapes. The reduction of Ag(NH 3 ) 2 + by HTAB (n-hexadecyltrimethylammonium bromide) gave Ag NPs of different morphologies: cubes, triangles, wires, and aligned wires. Ag NPs synthesis by irradiation of Ag + ions does not involve a reducing agent and is an appealing procedure. Eco-friendly bio-organisms in plant extracts contain proteins, which act as both reducing and capping agents forming stable and shape-controlled Ag NPs. The synthetic procedures of polymer-Ag and TiO 2 -Ag NPs are also given. Both Ag NPs and Ag NPs modified by surfactants or polymers showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. The mechanism of the Ag NP bactericidal activity is discussed in terms of Ag NP interaction with the cell membranes of bacteria. Silver-containing filters are shown to have antibacterial properties in water and air purification. Finally, human and environmental implications of Ag NPs to the ecology of aquatic environment are briefly discussed.

A novel biological method for the synthesis of silver nanoparticles using the fungus Verticillium is reported. Exposure of the fungal biomass to aqueous Ag + ions resulted in the intracellular reduction of the metal ions and formation of silver nanoparticles of dimensions 25 ± 12 nm. Electron microscopy analysis of thin sections of the fungal cells indicated that the silver particles were formed below the cell wall surface, possibly due to reduction of the metal ions by enzymes present in the cell wall membrane. The metal ions were not toxic to the fungal cells and the cells continued to multiply after biosynthesis of the silver nanoparticles.

The photoconversion of photomorphic silver nanoparticles from
discs to prisms via citrate mediated growth on the twin plane
faces of the nanoparticles is demonstrated. This systematic
shape evolution from discs to hexagons and then prisms of
increasing aspect ratios is a result of the growth process being
confined to specific faces of the growing nanoparticles.

Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of Na-4 mica template. The specimens show magnetodielectric effect at room temperature with a change of dielectric constant as a function of magnetic field, the electric field frequency varying from 100 to 700 kHz. A decrease of 5% in the value of dielectric constant was observed up to a field of 1.2 Tesla. This is explained by an inhomogeneous two-component composite model as theoretically proposed recently. The present approach will open up synthesis of various nanocomposites for sensor applications.

Surface-enhanced Raman scattering (SERS) is a powerful technique used for obtaining chemical information about the molecules and molecular structures in the vicinity of surfaces of noble metal nanostructures. The chemical information acquired through SERS can be used for not only characterization but also detection and identification. In a clinical setting, rapid and accurate identification of micro-organisms is critical. The biochemical information collected through the SERS spectra can be used for quick identification of micro-organisms. The concentrated silver colloidal nanoparticles (AgNPs) are simply mixed with micro-organisms after culturing, and their SERS spectra acquired. Since the nanoparticles are in contact with the cell wall of the micro-organism, the biochemical information obtained is mostly assumed as originating from the cell wall which the AgNPs are in contact with, and is considered as the ‘fingerprint’ of the micro-organism, which can be used for the identification. Since a SERS spectrum can be acquired only in seconds, the obtained spectrum can be used for fast micro-organism identification. The reproducibility of the spectra obtained from micro-organisms is first tested, and then the obtained spectra are used for the goal. The identification of micro-organisms in mixtures is also attempted in model mixtures. It is demonstrated that the SERS can be used for fast and accurate identification of micro-organisms such as bacteria and yeast, even in their mixtures. Four bacteria, i.e. Shigella sonnei, Erwinia amylovara, Proteus vulgaris and DH5α (E. coli strain), and three yeast cells, i.e. Hyphopichia burtonii, Candida parapsilosis and Filobasidiella neoformans are used as model micro-organisms in the study.

Surface plasmon polaritons launched at concentric arcs can be focused into a subwavelength wide focal spot of high near-field light intensity. The focused plasmons give rise to enhanced Raman scattering from R6G molecules placed in the focal area. By exploiting the polarization dependence of the focusing the authors establish an enhancement of the Raman signal by a factor of 6. The results show that focusing of propagating surface plasmons on flat metal surfaces may be an
alternative to localized plasmons on metal nanostructures for achieving enhanced Raman scattering. In particular, a flat metal substrate enables better control over the local electric fields and the placement of analyte molecules, and, therefore, ultimately better fidelity of Raman spectra.
© 2007 American Institute of Physics. DOI: 10.1063/1.2759985

The present study demonstrates an eco-friendly and low cost protocol for synthesis of silver nanoparticles using the cell-free filtrate of Aspergillus flavus NJP08 when supplied with aqueous silver (Ag+) ions. Identification of the fungal isolate was based on nuclear ribosomal DNA internal transcribed spacer (ITS) identities. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed the formation of spherical metallic silver nanoparticles. The average particle size calculated using Dynamic Light Scattering measurements (DLS) was found to be 17 nm. UV-Visible and Fourier transform infrared (FTIR) spectroscopy confirmed the presence of extracellular proteins. SDS-PAGE profiles of the extracellular proteins showed the presence of two intense bands of 32 and 35 kDa, responsible for the synthesis and stability of silver nanoparticles, respectively. A probable mechanism behind the biosynthesis is discussed, which leads to the possibility of using the present protocol in future ‘‘nano-factories’’.

Here we describe a simple, powerful technique based on the laser ablation of a target immersed in a water solution of a metal salt. With this method, nanoparticles of different metals and alloys can be processed very quickly. Both the target and the salt solution can be chosen to produce metal nanoparticles of different sizes, surface-oxidized nanoparticles (silica−silver, for example), or even more complex structures to be defined by the researcher on one or more steps because the technique combines the advantages of both physical and chemical methods. We have applied this technique to the fabrication of inert silica−metal (silver, gold, and silver−gold) nanoparticles with a strong surface plasmon resonance all together in a single step. The advantage of the simultaneous production of silica during laser ablation is the stabilization of the metal nanoparticle colloid but also the possibility to reduce the toxicity of these nanoparticles.

The fluorescence from a single molecule can be strongly enhanced near a metal nanoparticle acting as an optical antenna. We demonstrate the spectral tunability of this antenna effect and show that maximum enhancement is achieved when the emission frequency is red-shifted from the surface plasmon resonance of the particle. Our experimental results, using individual gold and silver particles excited at different laser-frequencies, are in good agreement with an analytical theory which predicts a different spectral dependence of the radiative and non-radiative decay rates.

In this work, the formation of silver metal nanoparticles inside a negative-tone resist based on poly(vinyl alcohol) is achieved by electron beam lithography. The chemistry of this sensitive resist allows the production of nanoparticles as well as the polymer crosslinking by the electron radiation. Due to the presence of the silver nanoparticles, the final composite exhibits a plasmonic behavior, which was characterized by measuring the absorbance. The lithographic properties of the resist have been characterized.

The antibacterial properties of silver modified montmorillonites from Pellegrini Lake, Argentina were tested in growth inhibition of Escherichia
coli bacteria. Montmorillonite was first submitted to different treatments: (a) calcination at 550 ◦C for 3 h and (b) grinding during 300 s. After that,
the samples were loaded with silver by ion exchange. Structural characterization was performed by X-ray diffraction (XRD), Fourier transformed
infrared spectroscopy (FTIR), and BET specific surface area measurements. Scanning electron microscopy (SEM) and high resolution transmission
electron microscopy (HRTM) showed that metallic silver nanoparticles precipitates over the clay surface after silver modification. Nevertheless, the
displacement of the (0 0 1) reflection observed by XRD in the calcined sample, and the diminution in Na+ content evaluated by energy dispersive
X-ray spectroscopy (EDXS), indicate that Ag ions were interchanged in the structure of the clays. Both samples showed good antibacterial activity
against E. coli, measured by the disk susceptibility and the minimum inhibitory concentration (MIC) tests. The ground montmorillonite required
a lower MIC than the thermally treated, although the last one presented a bigger inhibition zone in the disk method. The results shows that the
antibacterial activity is generated by the Ag+ present in the clay, as confirmed by X-ray photoelectronic spectroscopy (XPS); however the overall
antibacterial properties are affected by the availability of the ionic silver to be in contact with the bacteria.