Antibacterial properties of novel poly(methyl methacrylate) nanofiber containing silver nanoparticles

Poly(methyl methacrylate) (PMMA) nanofiber containing silver nanoparticles was synthesized by radical-mediated dispersion polymerization and applied to an antibacterial agent. UV-vis spectroscopic analysis indicated that the silver nanoparticles were continually released from the polymer nanofiber in aqueous solution. The antibacterial properties of silver/PMMA nanofiber against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria were evaluated using minimum inhibitory concentration (MIC), the modified Kirby-Bauer method, and a kinetic test. The MIC test demonstrated that the silver/PMMA nanofiber had enhanced antimicrobial efficacy compared to that of silver sulfadiazine and silver nitrate at the same silver concentration.     

In situ synthesis of water dispersible bovine serum albumin capped gold and silver nanoparticles and their cytocompatibility studies

A simple and convenient one step room temperature method is described for the synthesis of bovine serum albumin (BSA) capped gold and silver nanoparticles. BSA reduces silver ions to silver nanoparticles but does not directly reduce gold ions to gold nanoparticles at room temperature and varying pH conditions. However, when silver and gold ions are simultaneously added to BSA, silver ions get reduced to metallic silver first and these in turn reduce gold ions to gold nanoparticles through a galvanic exchange reaction. The so synthesized silver and gold nanoparticles are easily water dispersible and can withstand addition of salt even at high concentrations. It is shown that the capped protein retains its secondary structure and the helicity to a large extent on the nanoparticles surface and that the protein capping makes the nanoparticles cytocompatible.     

Electrostatic-assembly metallized nanoparticles network by DNA template

Eighteen-nanometer gold and 3.5-nm silver colloidal particles closely packed by cetyltrimethylammonium bromide (CTAB) to form its positively charged shell. The DNA network was formed on a mica substrate firstly. Later, CTAB-capped gold or silver colloidal solutions were cast onto DNA network surface. It was found that the gold or silver nanoparticles metallized networks were formed owing to the electrostatic-driven template assembling of positive charge of CTAB-capped gold and silver particles on the negatively charged phosphate groups of DNA molecules by the characterizations of AFM, XPS and UV-vis. This method may provide a novel and simple way to studying nanoparticles assembly conjugating DNA molecules and offer some potential promising applications in nanocatalysis, nanoelectronics, and nanosensor on the basis of the fabricated metal nanoparticles network.     

Phthalocyanine macrocycle as stabilizer for gold and silver nanoparticles

A one-step process was used for the preparation of gold and silver nanoparticles stabilized by an aminophthalocyanine macrocycle. The resultant nanoparticles were characterized by absorption spectra, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The nanoparticles were found to possess relatively narrow size distribution. The gold nanoparticles have an average diameter of ~2 nm, while silver particles have 4–5 nm. Preliminary studies on fluorescence and surface enhanced Raman spectroscopy were carried out using these nanoparticles. Fluorescence studies indicate that gold nanoparticles do not quench the fluorescence, while silver nanoparticles do. The stabilized nanoparticles showed enhancement of the Raman signals, thus revealing that they are good substrates for surface enhanced Raman scattering studies.     

Transmetalation reaction between hydrophobic silver nanoparticles and aqueous chloroaurate ions at the air-water interface

The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior.     

Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth

We report on the use of Neem (Azadirachta indica) leaf broth in the extracellular synthesis of pure metallic silver and gold nanoparticles and bimetallic Au/Ag nanoparticles. On treatment of aqueous solutions of silver nitrate and chloroauric acid with Neem leaf extract, the rapid formation of stable silver and gold nanoparticles at high concentrations is observed to occur. The silver and gold nanoparticles are polydisperse, with a large percentage of gold particles exhibiting an interesting flat, platelike morphology. Competitive reduction of Au3+ and Ag+ ions present simultaneously in solution during exposure to Neem leaf extract leads to the synthesis of bimetallic Au core-Ag shell nanoparticles in solution. Transmission electron microscopy revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core-shell structure. The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in our earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.     

Plant extract mediated synthesis of silver and gold nanoparticles and its antibacterial activity against clinically isolated pathogens

Biosynthesis of nanoparticles is under exploration is due to wide biomedical applications and research interest in nanotechnology. Bioreduction of silver nitrate (AgNO(3)) and chloroauric acid (HAuCl(4)) for the synthesis of silver and gold nanoparticles respectively with the plant extract, Mentha piperita (Lamiaceae). The plant extract is mixed with AgNO(3) and HAuCl(2), incubated and studied synthesis of nanoparticles using UV-Vis spectroscopy. The nanoparticles were characterized by FTIR, SEM equipped with EDS. The silver nanoparticles synthesized were generally found to be spherical in shape with 90 nm, whereas the synthesized gold nanoparticles were found to be 150 nm. The results showed that the leaf extract of menthol is very good bioreductant for the synthesis of silver and gold nanoparticles and synthesized nanoparticles active against clinically isolated human pathogens, Staphylococcus aureus and Escherichia coli.     

Size quantized formation and self-assembly of gold encased silver nanoparticles

Mixing aqueous dispersions of thiocyanate ion coated small (< 3.5 nm diameter) gold nanoparticles and EDTA covered larger (> 22 nm diameter) silver nanoparticles, results in the formation of robust gold encased silver nanoparticles; in contrast to using larger (> 11 nm diameter) gold nanoparticles which forms chained structures.     

多尺度结构Ag/PA6纳米纤维膜的制备及其催化性能

随着工业的进步,废水处理特别是印染废水的处理成为亟待解决的问题.银纳米粒子因其特殊的物理化学性能而表现出催化活性,但银纳米粒子的团聚限制了其使用,所以出现了一系列新的载体材料,如微球、薄膜和纤维等.其中电纺纳米纤维由于具有高比表面积,作为载体材料具有非常大的优势,而将常规电纺纳米纤维作为载体也已有报道.但是,将具有更高比表面积的电纺纳米纤维作为载体,特别是一种类似于树枝状结构的多尺度纳米纤维作为载体还鲜有报道.本文制备了一种多尺度结构的PA6纳米纤维膜,该纳米纤维膜由直径为50?120 nm的主纤维和10?50 nm的分支纤维构成;由于分支纤维的出现,多尺度结构纳米纤维膜的比表面积得到了提高,可以为银纳米粒子的负载提供更多附着位点.制备的多尺度结构纳米纤维膜通过银胶溶液浸渍成功地负载银纳米粒子,对制备的纳米纤维膜的形态、化学结构以及对亚甲基蓝的催化性能进行了探讨.SEM,EDS和TEM结果表明,银纳米粒子成功地负载在多尺度结构纳米纤维的表面,并且银纳米粒子的粒径以及负载量可以通过变换银胶溶液的浓度合理调控.此外,与常规PA6纳米纤维膜相比,多尺度结构纳米纤维膜更有利于银纳米粒子的分散,同样通过银胶溶液A浸渍,负载在多尺度结构纳米纤维上银纳米粒子粒径为8.6 nm,而负载在普通PA6纳米纤维上银纳米粒子粒径为11.2 nm.XPS分析表明,银纳米粒子成功地负载到多尺度结构纳米纤维上,并且经不同银胶溶液处理,纳米纤维膜的载银量不同.通过O的高能XPS分析发现,银纳米粒子与PA6分子间形成了配位键,这在一定程度上有利于Ag纳米粒子的固定,阻止了Ag纳米粒子的团聚.Ag/PA6纳米纤维膜以及多尺度结构Ag/PA6纳米纤维膜催化降解实验表明,多尺度结构Ag/PA6纳米纤维膜具有较高的催化活性,反应2 h后对10 mg/L亚甲基蓝的降解率达到98.13%,并且降解过程符合伪一级动力学.不同浸渍液浓度处理纳米纤维膜催化实验表明,Ag纳米粒子的大小以及含量都会影响纳米纤维的催化活性,纳米粒子粒径越小,其催化活性越高;不同NaBH4加入量催化体系催化实验表明,随着NaBH4加入量的增大,催化体系的降解率增高,其对催化体系的催化性能起着至关重要的作用;其他条件一定,随着染料初始浓度的增大,催化体系的催化性能下降;循环实验表明,经5次循环之后,其降解率仍高达83.5%,该纳米纤维膜具有一定的循环使用性能.     

Characteristics of polypyrrole electrodeposited onto roughened substrates composed of gold–silver bimetallic nanoparticles

In this work, the characteristics of polypyrrole (PPy) films electrodeposited onto an electrochemically roughened gold substrate with bimetallic silver and gold nanoparticles were first investigated. First, a silver substrate was roughened by a triangular‐wave oxidation–reduction cycle (ORC) in an aqueous solution containing 0.1 M HCl. Subsequently, a gold substrate was roughened by a similar ORC treatment in this used solution. The results revealed that the surface of the roughened gold substrate demonstrated two different kinds of deposition domains because of the modification of silver nanoparticles. Encouragingly, some novel characteristics of PPy deposited onto this substrate were observed, in comparison with those on the roughened gold substrate without the modification of silver nanoparticles. They included a denser and more compact surface morphology, higher oxidation degree, increased conductivity, and improved surface‐enhanced Raman scattering. Furthermore, the nucleation and growth mechanism for PPy electropolymerization on this silver‐modified roughened gold substrate was distinguishable from that on the unmodified one. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2724–2731, 2006     

Polymer-induced synthesis of stable gold and silver nanoparticles and subsequent ligand exchange in water

A simple, inexpensive, single-step synthesis of gold and silver nanoparticles using poly(allylamine) (PAAm) as a reducing and stabilizing agent is reported. The synthetic process was carried out in aqueous solution, making the method versatile and environmentally friendly. The synthesized polymer-stabilized nanoparticles are stable in water without particle aggregation at room temperature for at least a month. We demonstrate successful ligand exchange on the polymer-stabilized gold nanoparticles (AuNPs) with a variety of omega-functionalized acid-, alcohol-, amine-, and biotin-terminated alkylthiols. The methodologies, including ligand exchange, also are applicable for the generation of finely dispersed silver nanoparticles. The synthesized gold and silver nanoparticles are characterized by UV-visible absorption spectroscopy and transmission electron microscopy (TEM). The different ligand-stabilized AuNPs are also analyzed by Fourier transform infrared (FTIR) spectroscopy.     

Murraya Koenigii leaf-assisted rapid green synthesis of silver and gold nanoparticles

A facile bottom-up 'green' and rapid synthetic route using Murraya Koenigii leaf extract as reducing and stabilizing agent produced silver nanoparticles at ambient conditions and gold nanoparticles at 373 K. The nanoparticles were characterized using UV-vis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. This method allows the synthesis of well-dispersed silver and gold nanoparticles having size ～10 nm and ～20 nm, respectively. Silver nanoparticles with size ～10 nm having symmetric SPR band centered at 411 nm is obtained within 5 min of addition of the extract to the solution of AgNO3 at room temperature. Nearly spherical gold nanoparticles having size ～20 nm with SPR at 532 nm is obtained on adding the leaf extract to the boiling solution of HAuCl4. Crystallinity of the nanoparticles is confirmed from the high-resolution TEM images, selected area electron diffraction (SAED) and XRD patterns. From the FTIR spectra it is found that the biomolecules responsible for capping are different in gold and silver nanoparticles. A comparison of the present work with the author's earlier reports on biosynthesis is also included.     

Thermostimulated formation of silver and gold nanoparticles in porous silicon dioxide matrices

Manifestations of thermostimulated formation and subsequent transformation of silver and gold nanoparticles in porous opal and Vycor glass matrices are studied using optical spectroscopy. Two temperature ranges for silver nanoparticles are revealed, where first-type particles transform into another type of particles. With gold nanoparticles in these matrices, a temperature range in which one type of particles transforms into another type is established. An effect of complete blackening of Vycor glass samples, caused by their annealing, is revealed, and a rationalization of this effect is given.     

Application of nanoparticles for the enhancement of latent fingerprints

Two different types of nanoparticles dissolved in organic solution, gold stabilized by n-alkanethiols and CdSe/ZnS stabilized by n-alkane-amine, adhere preferentially to the ridges of latent fingerprints; the gold deposits catalyze silver electroless deposition from "Silver Physical Developer" (Ag-PD), an aqueous solution containing silver colloids stabilized by cationic surfactants, to form dark impressions of the ridge details; the hydrophobic capped gold nanoparticles significantly improve the intensity and clarity of the developed prints compared with Ag-PD alone; finger marks treated with CdSe/ZnS nanoparticles can be viewed directly, due to their fluorescence under UV illumination.     

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

We report a novel strategy for the biological synthesis of anisotropic gold and quasi-spherical silver nanoparticles by using apiin as the reducing and stabilizing agent. The size and shape of the nanoparticles can be controlled by varying the ratio of metal salts to apiin compound in the reaction medium. The resultant nanoparticles were characterized by UV-vis-NIR, transmission electron microscopy (TEM), FT-IR spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The interaction between nanoparticles with carbonyl group of apiin compound was confirmed by using FT-IR analysis. TEM photograph confirming the average size of the gold and silver nanoparticles were found to be at 21 and 39 nm. The NIR absorption of the gold nanotriangles is expected to be of application in hyperthermia of cancer cells and in IR-absorbing optical coatings.     

Hybridization of oligonucleotide-modified silver and gold nanoparticles in aqueous dispersions and on gold films

Functionalization of silver and gold nanoparticles by 12mer-thiolated homo-oligonucleotides, SA and ST (containing only adenine or thymine, respectively), and their hybridization and dehybridization in aqueous dispersions have been described. In addition, ST and SA were self-assembled onto gold films and hybridized with their complementary pairs, unlabeled or labeled by gold and silver nanoparticles. The base pairing between DNA strands and the types of oligonucleotides (adenine or thymine) attached to the nanoparticles was detected by Polarization Modulated Fourier Transform Infrared Reflection Absorption Spectroscopy (PM-FTIRRAS).     

Defining rules for the shape evolution of gold nanoparticles

The roles of silver ions and halides (chloride, bromide, and iodide) in the seed-mediated synthesis of gold nanostructures have been investigated, and their influence on the growth of 10 classes of nanoparticles that differ in shape has been determined. We systematically studied the effects that each chemical component has on the particle shape, on the rate of particle formation, and on the chemical composition of the particle surface. We demonstrate that halides can be used to (1) adjust the reduction potential of the gold ion species in solution and (2) passivate the gold nanoparticle surface, both of which control the reaction kinetics and thus enable the selective synthesis of a series of different particle shapes. We also show that silver ions can be used as an underpotential deposition agent to access a different set of particle shapes by controlling growth of the resulting gold nanoparticles through surface passivation (more so than kinetic effects). Importantly, we show that the density of silver coverage can be controlled by the amount and type of halide present in solution. This behavior arises from the decreasing stability of the underpotentially deposited silver layer in the presence of larger halides due to the relative strengths of the Ag(+)/Ag(0)-halide and Au(+)/Au(0)-halide interactions, as well as the passivation effects of the halides on the gold particle surface. We summarize this work by proposing a set of design considerations for controlling the growth and final shape of gold nanoparticles prepared by seed-mediated syntheses through the judicious use of halides and silver ions.     

Paper surfaces functionalized by nanoparticles

Nanomaterials with unique electronic, optical and catalytic properties have recently been at the forefront of research due to their tremendous range of applications. Taking gold, silver and titania nanoparticles as examples, we have reviewed the current research works on paper functionalized by these nanoparticles. The functionalization of paper with only a very small concentration of nanoparticles is able to produce devices with excellent photocatalytic, antibacterial, anti-counterfeiting, Surface Enhanced Raman Scattering (SERS) and Surface Plasmon Resonance (SPR) performances. This review presents a brief overview of the properties of gold, silver and titania nanoparticles which contribute to the major applications of nanoparticles-functionalized paper. Different preparation methods of the nanoparticles-functionalized paper are reviewed, focusing on their ability to control the morphology and structure of paper as well as the spatial location and adsorption state of nanoparticles which are critical in achieving their optimum applications. In addition, main applications of the nanoparticles-functionalized papers are highlighted and their critical challenges are discussed, followed by perspectives on the future direction in this research field. Whilst a few studies to date have characterized the distribution of nanoparticles on paper substrates, none have yet optimized paper as a nanoparticles' substrate. There remains a strong need to improve understanding on the optimum adsorption state of nanoparticles on paper and the heterogeneity effects of paper on the properties of these nanoparticles.     

The formation of mono- and bimetallic silver-containing seed nanoparticles

The regularities of the formation of mono- and bimetallic seed particles used for subsequent synthesis of anisotropic silver nanoparticles in micellar media has been studied. It has been found that the formation of nanosized silver seed particles is influenced by the synthesis parameters, such as the presence of oxygen and gold in the reaction system. Based on characteristics of the surface plasmon resonance band of nanoparticles, a simple and efficient method has been proposed for controlling the degree of monodispersity of the seed particles.     

Ultra-sensitive colorimetric method to quantitate hundreds of polynucleotide molecules by gold nanoparticles with silver enhancement.

An ultra-sensitive colorimetric method to quantitate hundreds of polynucleotide molecules by gold nanoparticles with silver enhancement has been developed. The hybridization products from the target polynucleotides with biotin-labeled probes and gold nanoparticle-functioned oligonucleotides were immobilized to microplates via avidin-biotin system, and the absorbance signals of gold nanoparticles were amplified by silver enhance solution. This sandwich colorimetric assay can detect as few as 600 molecules for single-strand oligonucleotides and as few as 6000 molecules for double-strand polynucleotides in a 50 microL reaction system.