Influence of Silver Nanoparticles on 2,3-Bis(Chloromethyl)Anthracene-1,4,9,10-Tetraone

Size effect of silver nano particles on the photophysical properties of 2,3-bis(chloromethyl)anthracene-1,4,9,10-tetraone (BCMAT) have been investigated using optical absorption and fluorescence emission techniques. Silver NPs of different sizes have been prepared by two different methods. Quenching of fluorescence of BCMAT has been found to increase with decrease in the size of the silver NPs. Stern–Volmer quenching constants have also been calculated.     

Surface-Enhanced Infrared Spectral Investigations of 2,3-Bis(chloromethyl)anthracene-1,4,9,10-tetraone on Copper Nanoparticles

ABSTRACT

Surface-enhanced infrared (IR) absorption spectroscopic technique has been employed to investigate the orientation of 2,3-bis(chloromethyl)anthracene-1,4,9,10-tetraone (BCMAT) on copper nanoparticles (NPs). Copper NPs have been prepared by the chemical reduction method. The observed ring stretching modes show higher downshifts, broader bandwidths, and higher enhancement. The observed features in out-of-plane and in-plane CH deformation modes indicate that the BCMAT molecules may be adsorbed in a “flat-on” orientation on the copper NPs. The observed lower enhancement factor of the in-plane C?O deformation mode and C?O stretching mode and the higher enhancement factor of out-of-plane C?O deformation mode elucidate that the BCMAT molecules are adsorbed on the copper NPs in a “flat-on” orientation. All these observations show that BCMAT is adsorbed on copper NPs through the π-anthraquinone ring system in a “flat-on” orientation.     

Effect of metallic nanoparticle sizes on the local field near their surface

We have used numerical calculations based on Mie theory to analyze the near field distribution patterns for 4–150 nm spherical silver nanoparticles (nanospheres). We have shown that as the nanoparticle sizes increase, the region where “hot spots” are concentrated is shifted to the forward hemisphere. We have observed a nonmonotonic dependence of the maximum attainable local field enhancement factor on the size of the silver nanospheres. We have determined a correlation between the optimal nanosphere size for the maximum attainable local field enhancement factor and the optical absorption efficiency factor. We have established a nonmonotonic dependence of the optimal size of the nanoparticles and the maximum attainable local field enhancement factor on the refractive index of the surrounding medium. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 831–837, November–December, 2008.     

Nonlinear optical properties of nanometer-size silver composite azobenzene containing polydiacetylene film

Diacetylene monomer containing p-nitrophenyl azobenzene moiety (NADA) was synthesized. Silver nanoparticles with different concentrations were adulterated in the above polymerized NADA (PNADA) films and the third-order nonlinear optical properties were investigated in detail. UV–vis spectra and transmission electron microscopy were used to confirm the formation of PNADA/Ag nanocomposite films. The silver nanoparticles (average size of 10 nm) were well dispersed in the polymer films. The value of the nonlinear refractive index n ₂ for PNADA films (8.48×10⁻¹⁵ cm²/W) was much higher than that of pure polydiacetylene films. Further, the introduction of silver nanoparticles into the PNADA polymer films led to the further enhancement of nonlinear optical properties. The maximum value of n ₂ for PNADA/Ag nanocomposite films could be 11.6×10⁻¹⁵ cm²/W. This enhancement should be ascribed to the surface plasmon resonance of silver nanoparticles.     

Spectral Investigations on N-(2-Methylthiophenyl)-2-Hydroxy-1-Naphthaldimine by Silver Nanoparticles: Quenching

The photo—physical properties of N-(2-methylthiophenyl)-2-hydroxy-1-naphthaldimine (NMTHN) on silver nano particles have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by two different methods. The increases in size of the silver nanoparticles cause a decrease in the quenching of fluorescence of NMTHN. Stern–Volmer quenching constants and the association constants have also been calculated.     

Determination of Enoxacin Using Tb Composite Nanoparticles Sensitized Luminescence Method

In our study, terbium-acetylacetone (Tb-acac) composite nanoparticles have been prepared under vigorous ultrasonic irradiation. The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorescence probes in the determination of enoxacin (Enox) based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution on the fluorescence intensity was investigated. Under the optimum conditions, the fluorescence intensity of the Tb-acac-Enox system is linearly proportional to the Enox concentration in the Enox concentration range of 2 × 10⁻⁷–1 × 10⁻⁴ M. The correlation coefficient for the calibration curve was 0.9976. The limit of detection as defined by IUPAC, C _LOD = 3S _b/m (where S _b is the standard deviation of the blank signals and m is the slope of the calibration graph) was found to be 3 × 10⁻⁸ M. The relative standard deviation (RSD) for six repeated measurements of 1 × 10⁻⁴ M Enox was 1.35%. The method was applied to the determination of Enox in pharmaceutical formulation and recovery results were obtained from urine samples.     

Strong Photoluminescence Enhancement from Colloidal Quantum Dot Near Silver Nano-Island Films

We present the fabrication and optical investigation of highly random self-assembled, nano-scale films, probing their influence on the luminescence properties of near surface CdSe/ZnS colloidal quantum dots. When compared to quantum dots distributed on unstructured quartz substrates, the average luminescence intensity is found to be enhanced by a factor of 160×. The silver nanoparticles are prepared using slow thermal evaporation on quartz substrates and post-deposition annealing to produce a randomly-arranged layer of smooth nano-islands. Clear polarization dependent hot spots are observed. Such hot spots deliver a maximal enhancement of the emission intensity of 240× and have a spatial density of (0.050±0.002) μm^− 2. The results show that silver nano-island films strongly enhance the optical efficiency of near quantum dots emitters.     

Synthesis and characterization of silver nanoparticles: effect on phytopathogen <Emphasis Type="Italic">Colletotrichum gloesporioides</Emphasis>

Colloidal silver nanoparticles were synthesized by reducing silver nitrate solutions with glucose, in the presence of gelatin as capping agent. The obtained nanoparticles were characterized by means of UV–Vis spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The response surface methodology (RSM) was also used to determine the influence of the variables on the size of the nanoparticles. The antifungal activity of the silver nanoparticles was evaluated on the phytopathogen Colletotrichum gloesporioides, which causes anthracnose in a wide range of fruits. The UV–Vis spectra indicated the formation of silver nanoparticles preferably spherical and of relatively small size (<20 nm). The above-mentioned was confirmed by TEM, observing a size distribution of 5–24 nm. According to RSM the synthesis variables influenced on the size of the silver nanoparticles. By means of FTIR spectroscopy it was determined that gelatin, through their amide and hydroxyl groups, interacts with nanoparticles preventing their agglomeration. The growth of C. gloesporioides in the presence of silver nanoparticles was significantly delayed in a dose dependent manner.     

Kinetic aspects of the silver ion release from antimicrobial polyamide/silver nanocomposites

Spherical silver nanoparticles were grown in situ in different polyamides by a thermal reduction of silver acetate during melt processing of the polymers. Most of the particles have a diameter of about 20 nm. The absolute amount as well as the kinetics of the silver ion release from the various polyamide/silver nanocomposites differ strongly, although the filler content in all materials is the same (1.5 wt. %) and the morphologies of the silver particles are not very different. One result of the investigations was that the absolute amount of the long-term silver ion release increases exponentially with the maximum water absorption of the polymers used as matrix materials, because silver ions are formed from elemental silver particles in the presence of water, only. Moreover, it was also found that the long-term silver ion release increases with a growing diffusion coefficient of water in the polymer. The water absorption properties of the polymers govern the kinetics of the silver ion release, too: for strong hydrophilic polyamides like PA6 or PA6.6, which are plasticized by water, the silver ion release is a zero-order process. For nanocomposites with less hydrophilic polyamides like a cycloaliphatic polyamide or a P12 modified with polytetrahydrofurane (PA12-poly-THF), the silver ion release is governed by diffusion. As expected from the efficacy of the silver ion release, PA6, PA6.6, PA12 and PA12 modified with polytetrahydrofurane and a cycloaliphatic polyamide filled with 1.5 wt. % of silver nanoparticles are active against Escherichia coli. But, only nanocomposites with PA6, PA6.6 and P12-poly-THF as matrix materials are suitable as long-term biocidal materials. PACS 68.35.bm; 68.35.Fx; 68.37.Lp     

Fluorescence Quenching of 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone by Silver Nanoparticles: Size Effect

Size effect of silver nano particles on the photophysical properties of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by Creighton method using magnetic stirrer and ultrasonic field. Quenching of fluorescence of DHDMAQ has been found to increase with decrease in the size of the silver nanoparticles. Stern–Volmer quenching constants have also been calculated.     

Silvernanotherapy on the viral borne disease of silkworm <Emphasis Type="Italic">Bombyx mori</Emphasis> L.

Antiviral assays of chemically and biologically synthesized silver nanoparticles were made against BmNPV (Bombyx mori Nuclear Polyhedrosis Virus). Reduction of silver ions by sodium citrate and Spirulina platensis led to the formation of spherical silver nanoparticles of 40–60 and 7–16 nm size. Single cell protein (Spirulina platensis)-synthesized silver nanoparticles showed the strongest antiviral activity. Immunological studies made on the silkworm Bombyx mori disclosed that a significant increase in the total hemocyte count and differential hemocyte count due to S. platensis-synthesized silver nanoparticles supplementation. Improvement in the defense mechanism was noticed from the strengthened peritrophic membrane of the digestive tract and the increased total protein. Overall, the results presented illustrate that single cell protein-synthesized silver nanoparticles supplementation is effective in controlling viral-borne diseases of the silkworm.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.     

Use of a silver ion selective electrode to assess mechanisms responsible for biological effects of silver nanoparticles

For a detailed analysis of the biological effects of silver nanoparticles, discrimination between effects related to the nano-scale size of the particles and effects of released silver ions is required. Silver ions are either present in the initial particle dispersion or released by the nanoparticles over time. The aim of this study is to monitor the free silver ion activity {Ag⁺} in the presence of silver nanoparticles using a silver ion selective electrode. Therefore, silver in the form of silver nanoparticles, 4.2 ± 1.4 nm and 2–30 nm in size, or silver nitrate was added to cell culture media in the absence or presence of A549 cells as a model for human type II alveolar epithelial cells. The free silver ion activity measured after the addition of silver nanoparticles was determined by the initial ionic silver content. The p {Ag⁺} values indicated that the cell culture media decrease the free silver ion activity due to binding of silver ions by constituents of the media. In the presence of A549 cells, the free silver ion activity was further reduced. The morphology of A549 cells, cultivated in DME medium containing 9.1% (v/v) FBS, was affected by adding AgNO₃ at concentrations of ≥30 μM after 24 h. In comparison, silver nanoparticles up to a concentration of 200 μM Ag did not affect cellular morphology. Our experiments indicate that the effect of silver nanoparticles is mainly mediated by silver ions. An effect of silver on cellular morphology was observed at p {Ag⁺} ≤ 9.2.     

Green synthesis of silver nanoparticle by <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis> NPMF: the process and optimization

An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO₃ increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO₃ concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.     

Highly bacterial resistant silver nanoparticles: synthesis and antibacterial activities

In this article, we describe a simple one-pot rapid synthesis route to produce uniform silver nanoparticles by thermal reduction of AgNO₃ using oleylamine as reducing and capping agent. To enhance the dispersal ability of as-synthesized hydrophobic silver nanoparticles in water, while maintaining their unique properties, a facile phase transfer mechanism has been developed using biocompatible block co-polymer pluronic F-127. Formation of silver nanoparticles is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy. Hydrodynamic size and its distribution are obtained from dynamic light scattering (DLS). Hydrodynamic size and size distribution of as-synthesized and phase transferred silver nanoparticles are 8.2 ± 1.5 nm (σ = 18.3%) and 31.1 ± 4.5 nm (σ = 14.5%), respectively. Antimicrobial activities of hydrophilic silver nanoparticles is tested against two Gram positive (Bacillus megaterium and Staphylococcus aureus), and three Gram negative (Escherichia coli, Proteus vulgaris and Shigella sonnei) bacteria. Minimum inhibitory concentration (MIC) values obtained in the present study for the tested microorganisms are found much better than those reported for commercially available antibacterial agents.     

纳米银与表面吸附荧光素的荧光性能的影响

研究了纳米银粒子对表面吸附荧光素(fluorescein,Fl)的荧光性能的影响。Fl溶液中加入纳米银粒子,Fl分子包覆在纳米银粒子表面形成Fl_n-Ag复合物使纳米银相互桥连形成类似网络的结构,且Fl分子吸收峰随着纳米银浓度的增加发生红移。纳米银通过产生的强局域场将能量传输给Fl发光中心,实现了Fl的荧光增强,荧光增强效率随着纳米银浓度的增加具有最大值。较大粒径的纳米银使Fl获得最大荧光增强效率所需浓度较低且最大荧光增强效率值较高。研究结果表明,纳米银与Fl间的能量传输主要由Fl分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程所决定并与纳米银的浓度、尺寸密切相关。     

Fluorescent silver nanoparticles via exploding wire technique

Aqueous solution containing spherical silver nanoparticles of 20–80 nm size have been generated using a newly developed novel electro-exploding wire (EEW) technique where thin silver wires have been exploded in double distilled water. Structural properties of the resulted nanoparticles have been studied by means of X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The absorption spectrum of the aqueous solution of silver nanoparticles showed the appearance of a broad surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. The theoretically generated SPR peak seems to be in good agreement with the experimental one. Strong green fluorescence emission was observed from the water-suspended silver nanoparticles excited with light of wavelengths 340, 360 and 390 nm. The fluorescence of silver nanoparticles could be due to the excitation of the surface plasmon coherent electronic motion with the small size effect and the surface effect considerations     

Optical properties and ultrafast electron dynamics in gold–silver alloy and core–shell nanoparticles

Silver and gold are the two most popular metals used for many nanoparticle applications, such as surface enhanced Raman scattering or surface enhanced fluorescence, in which the local field enhancement associated with the excitation of the localized surface-plasmon–polariton resonance (SPR) is exploited. Therefore, tunability of the SPR over a wide energy range is required. For this purpose we have investigated core–shell nanoparticles composed of gold and silver with different shell thicknesses as well as the impact of alloying on these nanoparticles due to a tempering process. The nanoparticles were prepared by subsequent deposition of Au and Ag atoms or vice versa on quartz substrates followed by diffusion and nucleation. Their linear extinction spectra were measured as a function of shell thickness and annealing temperature. It turned out that different gold shell thicknesses on silver cores allow a tuning of the SPR position from 2.79 to 2.05 eV, but interestingly without a significant change on the extinction amplitude. Heating of core–shell nanoparticles up to only 540 K leads to the formation of alloy nanoparticles, accompanied by a back shift of the SPR to 2.60 eV. Calculations performed in quasi-static approximation describe the experimental results quite well and prove the structural assignments of the samples. In additional experiments, we applied the well-established persistent spectral hole burning technique to the alloy nanoparticles in order to determine the ultrafast dephasing time T ₂. We obtained a dephasing time of T ₂=(8.1±1.6) fs, in good agreement with the dephasing time of T _2,∞=8.9 fs, which is already included in the dielectric function of the bulk.     

A sunlight-induced method for rapid biosynthesis of silver nanoparticles using an <Emphasis Type="Italic">Andrachnea chordifolia</Emphasis> ethanol extract

In this study a sunlight-induced method for rapid synthesis of silver nanoparticles using an ethanol extract of Andrachnea chordifolia is described. The silver nitrate solutions (1 mM) containing the ethanol extract of Andrachnea chordifolia were irradiated by both sunlight radiation and by sunlight radiation passed through different colored filters (red, yellow or green). The smallest size of silver nanoparticles was obtained when a silver ion solution was irradiated for 5 minutes by direct sunlight radiation. Further examination of the shape and size and of the surface chemistry of these biogenic silver nanoparticles, which were prepared under sunlight radiation, was carried out using transmission electron microscopy and infrared spectroscopy, respectively. Transmission electron microscopy images show spherical particles with an average size of 3.4 nm. Hydroxyl residues were also detected on the surface of these biogenic silver nanoparticles fabricated using plant extract of Andrachnea chordifolia under sunlight radiation. Our study on the reduction of silver ions by this plant extract in darkness shows that the synthesis process can take place under dark conditions at much longer incubations (48 hours). Larger silver polydispersed nanoparticles ranging in size from 3 to 30 nm were obtained when the silver ions were treated with the ethanol extract of Andrachnea chordifolia under dark conditions for 48 hours.     

Fabrication and characterization of SERS‐active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4‐aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS‐based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80–100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 × 10⁴ relative to silver colloid, which might have resulted from the presence of ‘hot‐spots’ at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 × 10⁷ by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface. SERS‐based Raman mapping technique in the form of line scanning further illustrates the good SERS activity and reproducibility on the silver clusters. Finally, 4‐mercaptopyridine (4‐Mpy) was chosen as an analyte and the lowest detected concentration was investigated by the SERS‐active silver clusters. A concentration of 1.6 × 10⁻¹⁰ M 4‐Mpy could be detected with the SERS‐active silver clusters, showing the great potential of the technique in practical applications of microanalysis with high sensitivity. Copyright © 2006 John Wiley & Sons, Ltd.