Variable Frequency Microwave Synthesis of Silver Nanoparticles

Synthesis of silver nanoparticles based on a polyol process and variable frequency microwave (VFM) was investigated. Comparing to a thermal method, the reaction by VFM radiation was much faster. The effects of silver nitrate concentration, poly(N-vinylpyrrolidone) (PVP) concentration, reaction time and reaction temperature were studied. It was found that the higher concentration of silver nitrate, longer reaction time and higher temperature increased the particle size while the higher concentration of PVP decreased the particle size.     

Gas-phase Crystallization of Titanium Dioxide Nanoparticles

We have investigated the development of crystal morphology and phase in ultrafine titanium dioxide particles. The particles were produced by a droplet-to-particle method starting from propanolic titanium tetraisopropoxide solution, and calcined in a vertical aerosol reactor in air. Mobility size classified 40-nm diameter particles were conveyed to the aerosol reactor to investigate particle size changes at 20–1200°C with 5–1-s residence time. In addition, polydisperse particles were used to study morphology and phase formation by electron microscopy. According to differential mobility analysis, the particle diameter was reduced to 21–23-nm at 600°C and above. Precursor decomposition occurred between 20°C and 500°C. The increased mobility particle size at 700°C and above was observed to coincide with irregular particles at 700°C and 800°C and faceted particles between 900°C and 1200°C, according to transmission electron microscopy. The faceted anatase particles were observed to approach a minimized surface energy by forming {101} and {001} crystallographic surfaces. Anatase phase was observed at 500–1200°C and above 600°C the particles were single crystals. Indications of minor rutile formation were observed at 1200°C. The relatively stable anatase phase vs. temperature is attributed to the defect free structure of the observed particles and a lack of crystal–crystal attachment points.     

Gas and Pressure Dependence for the Mean Size of Nanoparticles Produced by Laser Ablation of Flowing Aerosols

Silver nanoparticles were produced by laser ablation of a continuously flowing aerosol of microparticles entrained in argon, nitrogen and helium at a variety of gas pressures. Nanoparticles produced in this new, high-volume nanoparticle production technique are compared with our earlier experiments using laser ablation of static microparticles. Transmission electron micrographs of the samples show the nanoparticles to be spherical and highly non-agglomerated under all conditions tested. These micrographs were analyzed to determine the effect of carrier gas type and pressure on size distributions. We conclude that mean diameters can be controlled from 4 to 20 nm by the choice of gas type and pressure. The smallest nanoparticles were produced in helium, with mean sizes increasing with increasing molecular weight of the carrier gas. These results are discussed in terms of a model based on cooling via collisional interaction of the nanoparticles, produced in the laser exploded microparticle, with the ambient gas.     

基于单个花状银纳米颗粒的表面增强拉曼散射效应研究

在室温下,以硝酸银为银源,抗坏血酸为还原剂,通过调节表面活性剂聚乙烯吡络烷酮的浓度,实现对花状银纳米颗粒的可控制备。利用扫描电子显微镜、原子力显微镜、X射线衍射和X射线能谱等手段检测并分析了材料的形貌结构和成分组成。实验结果表明,当聚乙烯吡络烷酮的浓度为0.1 mol/L时,所制备花状银纳米颗粒的表面结构达到最精细的状态且颗粒的尺寸达到微米量级,适合对单颗粒进行定位与光学性质研究。以结构最优化的花状银纳米颗粒为表面增强拉曼散射基底材料,以羟基苯甲酸为探针,对单个和少数颗粒的表面增强拉曼散射效应进行了研究,并借助暗场散射光谱分析了基底的表面增强拉曼散射机理。结果显示,该花状银纳米颗粒因其独特的表面结构为拉曼信号增强提供了大量“热点”。良好的拉曼性能以及较低的制备成本表明,该新型表面增强拉曼散射基底具有很大的应用前景。     

Green Synthesis of Silver Nanoparticles at Room Temperature Using Kiwifruit Juice

Comparing with physical and chemical methods, green synthesis techniques are emerging as facile and eco-friendly methods for the synthesis of silver nanoparticles. In this work, we demonstrated the biological synthesis of silver nanoparticles by the reduction of silver ions using kiwifruit juice as the reducing and stabilizing reagent. From the evidence of ultraviolet-visible spectroscopy and transmission electron microscopy, different sizes of silver nanoparticles were formed when the juice volume, reaction temperature, and reaction time were altered with respect to 0.01% silver acetate solution. The synthesized silver nanoparticles were stable for more than 1 month. Transmission electron microscopy studies showed the silver nanoparticles synthesized in room temperature have the diameters in the range of 5–25 nm. The proposed synthesis method is green and low cost, and the synthesized silver nanoparticles have potential bioanalytical applications.     

The Toxicity of Silver Nanoparticles Depends on Their Uptake by Cells and Thus on Their Surface Chemistry

A set of three types of silver nanoparticles (Ag NPs) are prepared, which have the same Ag cores, but different surface chemistry. Ag cores are stabilized with mercaptoundecanoic acid (MUA) or with a polymer shell [poly(isobutylene‐alt‐maleic anhydride) (PMA)]. In order to reduce cellular uptake, the polymer‐coated Ag NPs are additionally modified with polyethylene glycol (PEG). Corrosion (oxidation) of the NPs is quantified and their colloidal stability is investigated. MUA‐coated NPs have a much lower colloidal stability than PMA‐coated NPs and are largely agglomerated. All Ag NPs corrode faster in an acidic environment and thus more Ag(I) ions are released inside endosomal/lysosomal compartments. PMA coating does not reduce leaching of Ag(I) ions compared with MUA coating. PEGylation reduces NP cellular uptake and also the toxicity. PMA‐coated NPs have reduced toxicity compared with MUA‐coated NPs. All studied Ag NPs were less toxic than free Ag(I) ions. All in all, the cytotoxicity of Ag NPs is correlated on their uptake by cells and agglomeration behavior.     

银纳米颗粒对掺铒铋酸盐玻璃光谱性质的影响

采用传统熔融淬火技术制备了一系列Er3+离子掺杂复合银纳米颗粒的铋酸盐玻璃样品.研究了纳米银含量的改变对Er3+离子荧光发射特性的影响.研究发现,铒在1.53 μm处的荧光强度在银纳米颗粒质量分数为0.2%处取得最大值,为未掺杂银纳米颗粒时的4.6倍.其荧光增强的原因归结于银纳米颗粒表面等离子体共振导致局域场增强和Ag...     

Spontaneous Agglomeration of Silver Nanoparticles Deposited on Carbon Film Surface

The spontaneous aggregation of silver nanoparticles on a two-dimensional surface at room temperature is investigated. The nanoparticles were deposited on a carbon film and have been observed by a transmission electron microscope (TEM) for over one year. These particles were about 10nm, spherical and well dispersed initially, and an obviously spontaneous agglomeration was observed at the 12th day, the values, coverage rate of the silver particles on carbon film, were increased with time (before 40th day), but reduced with time (after 40th day). These show that the aggregates of the particles tend to have the smallest surface to reduce their surface free energy and are compact three-dimensional cluster in which the most size is above 100nm. Agglomerating is a successively slow diffusion-limited aggregation (DLA) growth. Another phenomenon, a big aggregate gathering some particles and a small aggregate to form a still bigger one, is observed. This indicates that the aggregating processes are controlled by migration of the particles on carbon film surface and surface energy of the particles.     

纳米银对表面吸附核黄素分子光谱性质的影响

采用氧化还原法制备了纳米尺寸的银溶胶,研究了纳米银粒子对核黄素(Riboflavin,Ri)水溶液吸收光谱和荧光光谱的影响.Ri溶液中加入纳米银粒子,随着纳米银浓度的增大,吸收强度不断增强,372 nm处吸收峰红移,而444 nm处吸收峰蓝移,同时发生荧光猝灭现象.从无辐射通道增强、纳米银表面局域场减弱及Ri分子第一激...     

纳米银溶胶的制备及利用其SERS效应检测BPA的研究

制备了银溶胶作为表面增强活性基底,以此为基础详细研究了BPA的表面增强拉曼光谱(SERS)。研究了促凝剂氯化钠的加入对增强效果的影响。实验结果表明,当BPA乙醇溶液的浓度低至10-7g/mL时,依然可以得到明显的SERS信号。此方法操作简便快捷,无需对样品进行预处理,在BPA的快速检测方面具有很大应用潜力。     

银和去合金银-金纳米粒子的SERS活性研究

用乙二醇还原硝酸银,聚乙烯吡咯烷酮作表面活性剂合成了大量的银纳米颗粒。银纳米颗粒和HAuCl4发生置换反应后形成去合金银-金纳米粒子。以吡啶和SCN-作为探针分子研究了它们的SERS活性。结果表明,当探针分子吸附于银纳米颗粒和去合金银-金纳米粒子上时,探针分子的特征振动峰强度增强、频率发生位移。SERS可表征纳米粒子物理和化学性质的变化。     

Optimized Synthetic Protocols for Preparation of Versatile Plasmonic Platform Based on Silver Nanoparticles with Pentagonal Symmetries

The key findings in the synthesis and transformation of silver nanoparticles with pentagonal symmetries arising from regular multiple twinning are reported, researched in the last 5 years. In a one‐stage photochemical synthesis of silver decahedral (pentagonal bipyramid, J₁₃ solid) nanoparticles (AgDeNPs), oxidative etching by hydrogen peroxide is implemented to achieve complete conversion of the small silver platelet precursor NPs. The concentration of hydrogen peroxide is found to be optimal at 0.2 m . Such high peroxide concentration can be rationalized by its slow reactivity in a red‐ox equilibrium with borohydride and citrate. We have also adapted light‐emitting diodes (LEDs) as a light source and documented optimal exposure time, LED power, and wavelength range for convenient laboratory synthesis of high‐purity size‐selected AgDeNPs. In the absence of platelet impurities, AgDeNPs produce by the new‐generation procedure can be conveniently re‐grown into larger sizes using silver ions as a precursor. Thermal regrowth of new‐generation AgDeNPs into pentagonal silver nanorods (AgPRNPs, J₁₅ solid) can be reliably accomplished with the precise variation in rod length (by varying amounts of added silver) and width (by using different seed AgDeNPs). With the reported reproducible synthetic protocols that can be readily implemented in any chemistry laboratory, AgDeNPs and AgPRNPs should serve as a versatile plasmonic platform with a precisely tunable surface plasmon resonance (SPR) from ca. 430 nm (rounded AgDeNPs) to 1100+ nm (longitudinal SPR of longer AgPRNPs). The plasmonic platform based on the reported AgNPs with pentagonal symmetries should be practical for a diverse range of applications, especially plasmonic sensing and surface‐enhanced Raman spectroscopy.     

Protein Corona Modulates Distribution and Toxicological Effects of Silver Nanoparticles In Vivo

Exploitation of silver nanoparticles (AgNPs) in biomedicine represents more than one third of their overall applications. Despite their wide use, detailed toxicokinetic data and information on their action mechanisms in vivo are still scarce. One important obstacle is their fate and transformation patterns in biological environments where AgNPs get a “new face” after interaction with biomolecules, particularly proteins. The impact of protein corona on AgNP effects in vivo is eludicated. The in vivo effects of AgNPs prepared with two different protein coronas, albumin, and metallothionein, with polymer‐coated AgNPs are compared in male and female Wistar rats after intravenous administration. The results demonstrate that the character of the protein coronas on the AgNP surface affects not only distribution, but also oxidative stress response and genotoxicity in tissues of rat exposed to AgNPs. Additionally, sex‐related effects are observed. By emphasizing the importance of protein corona formation and sex‐related response, the obtained data support a reliable evidence base needed for assessing the health risks of the steadily increasing human exposure to AgNPs.     

Study on Synthesis of Silver Nanoparticles Using dsDNA as Template and Detection of GSH

In this work, silver nanoparticles are synthesized using a simple and sensitive method by using double-stranded DNA (dsDNA-Ag NPs) as a template. The prepared dsDNA-Ag NPs are characterized by fluorescence spectroscopy analysis, X-ray photoelectron spectroscopy analysis, and transmission electron microscopy analysis. The excitation wavelength of the prepared silver nanoparticles is 295 nm, the emission wavelength is 377 nm, the average particle size is 11.2 nm, and the dispersion is uniform with pleasurable stability. The nanomaterials are used as fluorescent probes to detect glutathione (GSH). After adding glutathione to the dsDNA-Ag NPs fluorescent probes, the fluorescence of dsDNA-Ag NPs is burst due to electron transfer and S Ag bond generation, and the linear range of detection concentration is 0–90 mm with a detection limit of 0.37 mm .     

光谱法研究pH值对纳米银及其与赖氨酸相互作用的影响

利用化学方法合成纳米银,调节pH值,加入赖氨酸溶液,通过紫外光谱和动态光散射法研究pH对纳米银及纳米银-赖氨酸体系稳定性的影响,利用表面增强拉曼光谱考察赖氨酸与纳米银的相互作用方式。紫外光谱显示纳米银和纳米银-赖氨酸体系在pH值为5~10时,均具有较强的吸收峰;应用动态光散射测定了不同pH的纳米银及其赖氨酸体系的粒径及强度自相关函数,在pH值为5~10时,粒径分布均匀,DLS自相关曲线平滑,说明纳米银和纳米银-赖氨酸体系稳定性良好;SERS研究了pH为4、7、10时,赖氨酸在银粒子表面的吸附作用,体系出现比较明显的赖氨酸特征峰,当pH为4时,为δ(NH3+)的1444cm~(-1)谱峰和δ(COO-)的1576cm~(-1),此时赖氨酸通过氨根和羧酸根共同与银纳米粒子发生相互作用,当pH为10时,NH_3~+发生去质子化,此时赖氨酸只出现COO-的伸缩振动在1576cm~(-1)处,说明此条件下赖氨酸以羧酸根吸附在银粒子表面。     

金银纳米粒子的电化学性质及联苯胺的SERS研究

采用柠檬酸钠还原氯金酸,硼氢化钠还原硝酸银分别制备了较小粒径的金、银纳米粒子。运用紫外可见吸收光谱(UV-Vis)、扫描电子显微镜(SEM)、循环伏安法(CV)对金、银纳米粒子进行了表征。结果表明：所得金、银纳米粒子粒径分别约为16和10 nm,并能以亚单层形式组装于导电玻璃(ITO)表面;CV图显示金、银纳米粒子分别有一对不对称的氧化还原峰,而且纳米粒子的浓度对其氧化还原电位存在一定的影响。采用自组装方法,以联苯胺为偶联分子, 在粗糙金基底表面构筑了金/银纳米粒子的双层有序结构。表面增强拉曼光谱研究表明, 在有序金银纳米粒子组装体中偶联分子的拉曼散射得到了增强。     

Phytosynthesis of Silver Nanoparticles Using Andrographis paniculata Leaf Extract and Evaluation of Their Antibacterial Activities

Use of nanotechnology in biological systems by the synthesis of metallic nanoparticles is a burning area of research in recent times. In the present investigation, aqueous extract of Andrographis paniculata was used to produce silver nanoparticles by reduction of silver nitrate. It was noted that the synthesizing process was quite rapid and silver nanoparticles form within minutes of silver ions coming in contact with plant extract. UV-Vis spectrum of the aqueous medium containing silver ions indicated a peak at 432 nm corresponding to the plasmon absorbance of the silver nanoparticles. Fourier transform infrared spectroscopic analysis of the silver nanoparticles showed the presence of proteins that might be acting as capping agents around the nanoparticles. From scanning electron microscopy analysis, the size of the silver nanoparticles was measured and it was found that the average size was between 40 and 60 nm. Furthermore, the antibacterial activity of synthesized silver nanoparticles exhibited effective inhibition zones against seven bacterial strains tested. Among the bacteria tested Pseudomonas aeruginosa was found to be most susceptible to the silver nanoparticles. Phytochemical screening of the plant extract indicated the presence of alkaloids, flavonoids, amino acids, saponins, tannins, and terpenoids.     

Enhanced Fluorescence from Periodic Arrays of Silver Nanoparticles

Electron beam lithography was used to fabricate silver nanoparticle arrays and study the effects of geometrical properties of particles on metal-enhanced fluorescence. Nanoparticle size, shape, interparticle spacing, and nominal thickness were varied in a combinatorial pattern for investigation of the particle plasmon resonance effect on enhancement of fluorescence from three different fluorophores; Fluorescein, Cy3, and Cy5. A specific geometric property for optimal enhancement from each fluorophore was determined. For interparticle spacings greater or equal to 270 nm, the enhancement matched what is expected for a single-particle model. For those particles smaller than 210 nm, the enhancement was lower than for the larger spacing in the range studied. Triangular-shaped particles gave similar enhancement to those of square-shaped particles. This combinatorial pattern by e-beam lithography was found to be useful for studying how individual parameters enhance the fluorescence that are important for rational design of enhanced fluorescence sensors.