Preparation of silver nanoparticles stabilized on the surface of polystyrene microspheres

Silver nanoparticles stabilized on the surface of polystyrene microspheres have been prepared by reducing silver ammine with formaldehyde, without surface activation of the microspheres. The size distributions of the nanoparticles have been obtained, and the optical absorption spectra of the synthesized nanomaterials have been measured.     

The microstructure and orientation of silver on NaCl: The influence of surface conditions

Silver films up to 1000 Å thick (coalescence stage and continuous films) were evaporated onto vacuum-cleaved NaCl at constant temperature and constant deposition rate but under various vacuum conditions (ultrahigh vacuum (UHV), high vacuum (oil pumped and ion pumped), a partial pressure of contaminant (10^-10–10^-6 Torr) etc.). The films were characterized by low energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy and transmission electron diffraction to determine their orientation, microstructure and cleanliness. The UHV-grown films were always polycrystalline. In contrast with previous observations, however, an increase in the partial pressure of H₂O alone did not improve the epitaxy. Hence the influence of other materials such as O₂, H₂O + O₂, hydrocarbons etc. was investigated. In addition, films were grown in UHV after pre-irradiation of the substrate with electrons and prenucleation at room temperature. If the prenucleated silver clusters were small and if their orientation was improved by annealing, continuous films were perfectly epitaxial even when the deposition of silver was carried out at room temperature after prenucleation. This indicates a post-nucleation mechanism of epitaxy.     

Photoelectron emission caused by surface plasmons in silver nanoparticles

A new intense band of photoelectron emission peaked at a wavelength of 490 nm has been observed in granular silver films with a nanoparticle size of 10–50 nm. Coinciding with an optical reflection band, the new photoelectron emission peak is related to the excitation of surface plasmons in silver nanoparticles. The quantum yield of photoemission (0.25%) for the new band is approximately equal to that for a longwave band of the classical silver-oxygen-cesium photocathode. It is demonstrated that the photoelectron emission from both photoemitters has a common nature and a time constant on the order of several femtoseconds can be obtained.     

Adherence inhibition of Streptococcus mutans on dental enamel surface using silver nanoparticles

The aim of this ex vivo study was to evaluate the adherence capacity of Streptococcus mutans after being exposed to three different sizes of silver nanoparticles on healthy human dental enamel. Three different sizes of silver nanoparticles (9.3, 21.3 and 98 nm) were prepared, characterized and an adherence testing was performed to evaluate their anti-adherence activity on a reference strain of S. mutans on healthy dental enamel surfaces. Colony-Forming Unit count was made for adherence test and light microscopy, atomic force microscopy and scanning electron microscopy were used to compare qualitative characteristics of S. mutans. 9.3 nm and 21.3 nm groups did not show differences between them but statistical differences were found when 9.3 nm and 21.3 nm groups were compared with 98 nm and negative control groups (p < 0.05). Microscopy analysis shows a better inhibition of S. mutans adherence in 9.3 nm and 21.3 nm groups than the 98 nm group when compared with control group. Silver nanoparticles showed an adherence inhibition on S. mutans and the anti-adherence capacity was better when silver nanoparticles were smaller.     

Effects of surface sterilisation with green synthesised silver nanoparticles on Lamiaceae seeds

Nanoparticles have been used in many areas of biotechnology. In this study, an alternative surface sterilisation method was established for plant tissue cultures. Silver nanoparticles synthesised via green synthesis were used for the surface sterilisation of Lamiaceae seeds (Salvia farinecae, Ocimum basilicum – Large Leaf Italian, Thymus vulgaris, Ocimum basilicum var. purpurascens). Water extracts of dried Alkanna tinctorum rhizomes and Syzygium aromaticum flowers were utilised in the bioreduction of silver ions. The seeds were exposed to 0, 1, 7, 14 and 28 day‐old colloidal solutions of silver nanoparticles and their effects on germination and surface sterilisation were determined. Fresh (0 and 1 day‐old) colloidal solutions of silver nanoparticles were found very effective on surface sterilisation (100%). Moreover, they showed no negative effect on both germination and morphology of plantlets. It was shown that silver nanoparticles can be used as a surface sterilisation agent and they have no adverse effects on seed germination and in vitro plantlet growth.Inspec keywords: nanoparticles, microorganisms, sterilisation (microbiological), silver, nanofabrication, antibacterial activity, colloids, nanobiotechnology, agricultureOther keywords: green synthesised silver nanoparticles, Lamiaceae seeds, silver ions, surface sterilisation agent, seed germination, colloidal solutions, surface sterilisation method, Ag     

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 μm and a depth of 1.5–2 μm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 μm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 μm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.     

Gold and silver nanoparticles surface functionalized with rhenium carbonyl complexes

Gold and silver nanoparticles have been synthesized and stabilized with 3-mercaptopropionic acid (MPA). The resulting MPA capped nanoparticles have been functionalized by attaching rhenium carbonyl species to the MPA carboxylate groups. The whole process have been carried out in a two-step procedure improved from the literature for radiopharmaceutical applications. The resultant rhenium-coated metal (gold or silver) nanoparticles have been studied by a different techniques, as for example X-ray photoelectron spectroscopy, UV–Visible spectroscopy, Z-potential, thermogravimetric analysis and vibrational infrared spectroscopy, which proves that the metal core has been really coated with the rhenium carbonyl species, so X-ray diffraction and transmission electron microscopy have been used to study the structure, size and shape of the obtained nanoparticles.     

Doubly localized surface plasmon resonance in bimodally distributed silver nanoparticles

Growth of bimodally distributed silver nanoparticles using sequential physical vapour deposition (PVD) is reported. Growth conditions of nanoparticles are defined in the following three steps: In the first step, nanoparticles are grown at a heated substrate and then exposed to atmosphere, in the second step, nanoparticles are vacuum annealed and finally re-deposition of silver is performed in the third step. This special way of deposition leads to the formation of bimodally distributed nanoparticles. It has been investigated that by changing the deposition time, different sets of bimodally distributed nanoparticles can be grown. Localized surface plasmon resonance (LSPR) of such bimodally distributed nanoparticles generates double plasmon resonance peaks with overlapped absorption spectra. Double plasmon resonance peaks provide a quick indication of the existence of two sets of nanoparticles. LSPR spectra of such bimodally distributed nanoparticles could be modeled with double Lorentz oscillator model. Inclusion of double Lorentz oscillator model indicates that there exist two sets of non-interacting nanoparticles resonating at different plasma frequencies. It is also reported that silver nanoparticles grown at a heated substrate, again attain the new shape while being exposed to atmosphere, followed by vacuum annealing at the same temperature. This is because of physisorption of oxygen at the silver surface and change in surface free energy. The re-shaping due to the adsorbed oxygen on the surface is responsible for bimodal size distribution of nanoparticles.     

Synthesis of silver nanoparticles using the polyol process and the influence of precursor injection

Spherical silver nanoparticles with various sizes and standard deviations were synthesized by the polyol process. Two different synthesis methods were compared in order to investigate the influence of reaction parameters on the resulting particle size and its distribution. In the precursor heating method, wherein a solution containing silver nitrate was heated to the reaction temperature, the ramping rate was determined to be a critical parameter affecting the particle size. In contrast, in the precursor injection method, in which a silver nitrate aqueous solution was injected into hot ethylene glycol, because of rapid nucleation, the injection rate and the reaction temperature were important factors in terms of reducing the particle size and attaining monodispersity. Silver nanoparticles with a size of 17 ± 2?nm were obtained at an injection rate of 2.5?ml?s(-1) and a reaction temperature of 100?°C.     

The influence of surface morphology and rigidity of the substrata on cell motility

The purpose of this study is to measure the cell motility under different stiffness and pattern of the substrata. Human melanoma cells were used for this study. Three surface patterns including flat, 6 µm-cone, and 6 µm-groove on polydimethylsiloxane (PDMS) were created by the micro-electro-mechanical system (MEMS). Glass dish was used as control substrate. After cells were seeded for 30 min, the cell images were taken every minute for 2 h. Each group had 4-5 dishes and 27-38 cells were calculated. The cell motility was 1.13 ± 1.30, 2.12 ± 1.21, 2.39 ± 1.11 and 3.08 ± 1.49 µm/min on glass, flat, cone, and groove PDMS, respectively. Cells in PDMS groups moved significantly faster than the control group (glass) due to smaller stiffness of the former substrates. More than 80% of cells on grooved PDMS moved along the grooves, indicating the grooved surface morphology could control the direction of cell movement. Our results display that substrate modulus and pattern can influence cell motility.     

The influence of implant surface properties on cell adhesion and proliferation

Interactions of the foreign material of implant and the living tissue on the cell level can cause prolonged healing or, worse, loss of the implant. The cell response to the presence of some implant materials was studied under in vitro conditions. The influence of physicochemical surface parameters on the response of the cells in the immediate vicinity of implants, namely on adhesion, proliferation and synthetic activity of fibroblasts, and on the blood coagulation were compared. The direct contact of tested materials (titanium and Ti6Al4V alloy with various surface treatments, Cr Co Mo alloy, hydroxyapatite-coated titanium, zirconium oxide ceramics, polyethylene and carbon composite) on cell spreading was monitored and the presence of TNF-α and IL-8 was evaluated in the cultivation medium. The formation of blood clots was investigated on samples immersed in a well with freshly drawn whole rabbit blood using a scanning electron microscope. The surface free energy was estimated using the measurement of static contact angle. Both the advancing and receding contact angles were measured by the dynamic Wilhemy plate method. Two main groups with extremes in cell viability were established. In the first group the increased polar component of surface free energy, the highest cell density, the lowest inflammatory cytokine production, but no fibres in the clotting blood were found. On the contrary, the second group of materials with a very low polar component of the surface free energy showed distinctly higher expression of inflammatory mediators, low cell proliferation, but faster formation of fibres in the blood coagulum.     

Phyto‐fabricated silver nanoparticles inducing microbial cell death via reactive oxygen species‐mediated membrane damage

Eco‐friendly synthesis of the silver nanoparticles (AgNPs) has a number of advantages like simplicity, biocompatibility, low toxicity in nature over their physical and chemical methods. In the present study, the authors report biosynthesized AgNPs using the root extract of the perennial plant ‘Spiny gourd’ (Momordica dioica) and investigated their anti‐bacterial application with mechanistic approaches. Different biophysical techniques such as UV‐Vis spectroscopy, FTIR, XRD, TEM, SAED, and DLS were employed for AgNPs characterization. The synthesized AgNPs were polydispersed, crystalline in nature, with anionic surface (−22.3 mV), spherical in shape with an average size of 13.2 nm. In addition, the AgNPs were stable in room temperature and in different biological buffers. The anti‐bacterial activities of AgNPs were studied with respect to the pathogens such as Bacillus subtilis, Staphylococcus aureus (Gram‐positive), Pseudomonas aeruginosa, Escherichia coli, Klebsiella planticola (Gram‐negative), and Candida albicans. Also, mechanistic studies of AgNPs such as protein leakage assay, nucleic acid leakage assay, ATP leakage assay, ROS accumulation, determination of biofilm degrading activity, measurement of potassium, showing that the synthesized AgNPs are capable of containing a potential application in the antimicrobial therapeutic agents and the pharmaceutical industry.     

The surface chemistry and stability of gold nanoparticles prepared using methanol extract of Eucalyptus camaldulensis

The development of nontoxic, clean techniques for synthesising metal nanoparticles such as gold has attracted increasing attention in recent years. Many reports have been published about the synthesis of gold nanoparticles using plant extracts. However, the stability of these prepared gold nanoparticles has not been investigated. In this research, the stability of gold nanoparticles prepared by Eucalyptus camaldulensis was investigated at different temperatures (4°C, 25°C and 45°C) for 8 weeks. Transmission electron microscopy and visible absorption spectroscopy confirmed the stability of gold nanoparticles during the storage period at the mentioned condition. In addition, Fourier transform–infrared spectroscopy was used to investigate the surface chemistry of gold nanoparticles prepared by the methanol extract of E. camaldulsis. The carboxyl group was characterised on the surface of the gold nanoparticles, and this functional group may have a critical role in the stability of gold nanoparticles prepared by the mentioned plant extract at different conditions. This functional group can be used for drug delivery of amino derivative drugs using gold nanoparticles.     

The influence of nanoparticles on polystyrene adhesion

The effect of silica nanoparticles on the adhesion of micron-sized polystyrene particles to a mica substrate has been investigated using a centrifuge to both ‘spin-on’ and ‘spin-off’ the polystyrene particles under different centrifuge conditions. In the absence of nanoparticles, the quantity of polystyrene particles removed increased steadily as the spin-off force was increased. The particle roughness and the number of particle–particle contacts were described as being responsible for this gradual removal.When nanoparticles were added, an increase in the overall removal of polystyrene particles under a given centrifugal force was seen, when compared to the water-only data. The greatest effect was observed for the lowest nanoparticle concentrations used. These results suggest that the interactions between nanoparticles and surfaces are complex and need to be studied in greater detail to thoroughly understand the particle detachment process.     

The influence of polymeric membrane surface free energy on cell metabolic functions

In membrane bioartificial organs using isolated cells, polymeric semipermeable membranes are used as immunoselective barriers, means for cell oxygenation and also as substrata for adhesion of anchorage-dependent cells. The selection of cytocompatible membranes that promote in vitro cell adhesion and function could be dependent on its membrane properties. In this study we investigated the physicochemical aspects of the interaction between the membrane and mammalian cells in order to provide guidelines to the selection of cytocompatible membranes. We evaluated the metabolic behavior of isolated liver cells cultured on various polymeric membranes such as the ones modified by protein adsorption. The physico-chemical properties of the membranes were characterized by contact angle measurements. The surface free energy of membranes and their different parameters acid (gamma+), base (gamma-) and Lifshitz-van der Waals (gammaLW) were calculated according to Good-van Oss's model. The adsorption of protein modified markedly both contact angle and membrane surface tension. In particular, membrane surface free energy decreased drastically with increased water contact angle. For each investigated membrane we observed that liver specific functions of cells improve on hydrophilic membrane surfaces. For all investigated membranes the rate of ammonia elimination increased with increasing of membrane surface free energy.     

影响贵金属纳米颗粒表面等离子体共振因素评述

贵金属纳米颗粒具有可调的共振吸收谱,被广泛用于光能传送器、近场扫描光学显微学、表面增强谱学、化学和生物传感器等。系统地评述了颗粒尺寸、颗粒分布、颗粒形状、颗粒体积分数、颗粒组成和颗粒结构等因素对金属纳米颗粒等离子体共振吸收性能的影响,有利于深入理解等离子体共振吸收的物理实质和实现对等离子体共振频率的调控。     

Morphology effects on the optical properties of silver nanoparticles

Employing methods developed for the control of shape and size in silver nanoparticles, we have compared the optical properties of nanorods, nanoprisms, nanodisks, and nanospheres. Solutions of these particles show distinct surface plasmon resonant absorption signatures that are directly correlated with the symmetries of their morphology. Nonlinear optical behavior for suspensions of these nanostructures, for nanosecond pulses at 532 and 1064 nm, have been correlated to plasmon resonances determined by shape and size.     

Enhanced third-order optical nonlinearity of silver nanoparticles with a tunable surface plasmon resonance

Poly(vinylalcohol) (PVA)-stabilized silver nanoparticles were prepared by a seeding method. Nanoparticles of varying morphology were obtained by controlled variation of the reaction conditions, and this method allowed the tailoring of the position of the surface plasmon resonance. The samples show two bands in the visible absorption spectrum: one in the 410-440-nm region and a second peak between 500 and 600 nm. This tunable surface plasmon resonance serves to increase the third-order optical nonlinearity (chi 3) of the nanoparticles (measured at 532 nm) by a factor of 16.