Synthesis of dendritic silver nanostructures by means of ultrasonic irradiation

In this paper, a simple and effective route for the synthesis of silver dendritic nanostructures by means of ultrasonic irradiation has been developed. Well-defined silver dendritic nanostructures were obtained by sonicating the aqueous solution of 0.04 mol/L silver nitrate with 4.0 mol/L isopropanol as reducing agent and 0.01 mol/L PEG400 as disperser for 2 h. The effects of the irradiation time, the concentration of Ag⁺ and the molar ratio of PEG to AgNO₃ on the morphology of silver nanostructures were discussed. The structures of the obtained samples were characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray powder diffraction (XRD), and the chemical composition of the dendrites was examined by energy-dispersive X-ray spectrum (EDS).     

Antifungal effects of 3D scaffold type gelatin/Ag nanoparticles biocomposite prepared by solution plasma processing

The 3D scaffold type biocomposites of gelatin/silver nanoparticles were prepared through the silver nanoparticles (Ag NPs) formation in gelatin solution using solution plasma process (SPP) and their antifungal activity was evaluated. The mixture of 3% gelatin solution and silver precursor (AgNO₃; 1–10 mM) was subject to discharge at high voltage (1600 V) under the controlled conditions to form the suspension of Ag NPs in the gelatin matrix. The freeze-drying process of lyophilization was employed to fabricate the 3D scaffold type biocomposite of gelatin/Ag NPs from the suspension. The water-insoluble property was improved by cross-linking using UV-irradiation (λ = 254 nm for 15 min). The physical and chemical characteristics of the biocomposite were investigated using UV–vis spectroscopy, EDS, FE-SEM, and TEM. The results indicated that the 3D scaffold biocomposite of gelatin/Ag NPs had spherical shape with approximately 11–12 nm of diameter. The antifungal activity analysis suggested that the biocomposite with Ag NPs could inhibit the growth of Candida albicans as well as that of hyphae and spores of Aspergillus parasiticus significantly. MIC of the biocomposite for C. albicans and A. parasiticus was determined as 80 μg/ml and 240 μg/ml of Ag NPs, respectively. The growth inhibition of 92.8% was observed in the biocomposite with 10 mM Ag against C. albicans.     

Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process

This paper aims to study fabrication and characterization of silver/titanium oxide composite nanoparticle through sonochemical process in the presence of ethylene glycol with alkaline solution. By using ultrasonic irradiation of a mixture of silver nitrate, the dispersed TiO₂ nanoparticle in ethylene glycol associated with aqueous solution of sodium oxide yields Ag/TiO₂ composite nanoparticle with shell/core-type geometry. The powder X-ray diffraction (XRD) of the Ag/TiO₂ composites showed additional diffraction peaks corresponding to the face-centered cubic (fcc) structure of silver crystallization phase, apart from the signals from the cores of TiO₂. Transmission electron microscopy (TEM) images of Ag/TiO₂ composites, which average particle size is roughly 80 nm, reveal that the titanium oxide coated by Ag nanoparticle with a grain size of about 2–5 nm. Additionally, the formation of silver nanoparticles on TiO₂ was monitored by ultraviolet visible light spectrophotometer (UV–Vis). As measured the optical absorption spectra of as-synthesized Ag nanoparticle varying with time, the mechanism of surface formatting silver shell on the cores of TiO₂ could be explored by autocatalytic reaction; the conversion of Ag particle from silver ion is 98% for the reaction time of 1000 s; and the activity energy of synthesizing Ag nanoparticles on TiO₂ is 40 kJ/mol at temperature ranging from 5 to 25 °C. Hopefully, this preliminary investigation could be used for mass production of composite nanoparticles assisted by ultrasonic chemistry in the future.     

Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach

Abstract  The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl₄ is greater than the AgNO₃ at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum. The case of low concentration of extract with HAuCl₄ offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal- or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state. Graphical abstract  Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent. The rate of bioreduction of AgNO₃ is lower than the HAuCl₄ at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration of phyllanthin with AgNO₃ and HAuCl₄.      

Spectroscopic investigation and Judd–Ofelt analysis of silver nanoparticles embedded Er3+-doped tellurite glass

A series of silver nanoparticles (NPs) embedded zinc-tellurite glass is prepared by melt-quenching technique. The transmission electron microscopic images reveal spherical as well as anisotropic silver NPs having average diameter in the range of 14–48 nm. The Er³⁺-free glass sample containing AgCl exhibits surface plasmon resonance (SPR) band of Ag NPs centered at ∼ 501 nm. From Judd–Ofelt analysis, it is found that by increasing the concentration of NPs, the value of Ω₂ is enhanced suggesting increased covalency and decreased symmetry around the Er³⁺ ions. Integrated emission cross-section (IEC) is enhanced as the concentration of silver NPs is increased up to 0.5 mol% AgCl. Fourier infrared spectra show that the intensity of the vibrational band of the water molecule and fundamental stretching band of OH group are suppressed. Furthermore, under an excitation wavelength of 786 nm, three prominent upconversion emissions are observed at 520 nm, 550 nm and 650 nm which are attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. The upconversion emissions are enhanced significantly by introduction of silver NPs. The enhancement is mainly attributed to the local field effect of silver NPs. Studied nanocomposites are potential candidates for the development of solid state lasers.     

Green synthesis of finely-dispersed highly bactericidal silver nanoparticles via modified Tollens technique

In this article, we represent a versatile and effective technique which using non-toxic chemicals to prepare stable aqueous dispersions of silver nanoparticles (NPs) via modified Tollens process. It was shown that as-prepared silver colloids consisted of finely-dispersed NPs with average diameter about 10 nm and a relatively narrow size distribution. Moreover, they could be stored very stable after several months without observation of aggregates or sedimentation. In comparison with previous works where Tollens process was being used, we for the first time applied UV-irradiation simultaneously with glucose reduction of silver salt through NPs preparation. The colloidal solutions of silver NPs were found to exhibit a high antibacterial activity against gram-negative Escherichia coli. The concentration of silver leading to a complete inhibition of bacteria growth was revealed as low as at 1.0 μg ml⁻¹ and found much lower compared to earlier reports. These advantages of aqueous dispersions of silver NPs make them ideal for green industrial, medicinal, microbiological and other applications.     

Hydrothermal synthesis of functionalized CdS nanoparticles and their application as fluorescence probes in the determination of uracil and thymine

A novel, sensitive, and convenient method for the determination of uracil and thymine by functionalized CdS nanoparticles (NPs) was proposed. CdS NPs were prepared by hydrothermal process and modified with thioglycollic acid (TGA) in aqueous solution. The fluorescence intensity of functionalized CdS NPs was quenched in the presence of uracil or thymine. Under optimal conditions, the relative fluorescence intensity (F₀/F) was proportional to the concentration in the range of 9.0×10^?6–1.0×10^?4 mol/L for uracil (r=0.9985) and 8.8×10^?7–1.5×10^?4 mol/L for thymine (r=0.9960). The corresponding detection limits were 9.6×10^?7 mol/L and 3.2×10^?7 mol/L, respectively. In addition, the possible quenching mechanism was also discussed.     

UV-induced synthesis,characterization and formation mechanism of silver nanoparticles in alkalic carboxymethylated chitosan solution

The silver nanoparticles (AgNPs) were synthesized in an alkalic aqueous solution of silver nitrate (AgNO₃)/carboxymethylated chitosan (CMCTS) with ultraviolet (UV) light irradiation. CMCTS, a water-soluble and biocompatible chitosan derivative, served simultaneously as a reducing agent for silver cation and a stabilizing agent for AgNPs in this method. UV–vis spectra and transmission electron microscopy (TEM) images analyses showed that the pH of AgNO₃/CMCTS aqueous solutions, the concentrations of AgNO₃ and CMCTS can affect on the size, amount of synthesized AgNPs. Further by polarized optical microscopy it was found that the CMCTS with a high molecular weight leads to a branch-like AgNPs/CMCTS composite morphology. The diameter range of the AgNPs was 2–8 nm and they can be dispersed stably in the alkalic CMCTS solution for more than 6 months. XRD pattern indicated that the AgNPs has cubic crystal structure. The spectra of laser photolysis of AgNO₃/CMCTS aqueous solutions identified the early reduction processes of silver cations (Ag⁺) by hydrated electron formed by photoionization of CMCTS. The rate constant of corresponding reduction reaction was 5.0 × 10⁹ M⁻¹ s⁻¹.     

Study on the interactions between anti-cancer drug oxaliplatin and DNA by atomic force microscopy

Oxaliplatin is one of the most important anticancer drugs at present. However, the mechanism of action of oxaliplatin is still controversial. In this study, the interactions between oxaliplatin and a plasmid DNA have been studied so as to reveal the structural basis of its activity. The structural characteristic of pUC19 DNA (2 ng/μL) incubated with 100 μmol/L and 1000 μmol/L of oxaliplatin for the different time on a freshly cleaved highly ordered pyrolytic graphite (HOPG) surface was investigated by atomic force microscopy (AFM). High resolution AFM observation indicated that oxaliplatin can induce pUC19 DNA molecules change from the extended conformation to the entangled structures with many nodes, and finally to the compact particles. The present AFM results provide structural evidence about the interactions between oxaliplatin and circular duplex DNA containing multiple targets.     

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.     

Determination of Paracetamol Based on its Quenching Effect on the Photoluminescence of CdTe Fluorescence Probes

L-Cysteine capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the determination of paracetamol was studied. The L-cysteine capped CdTe NPs were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry, ultraviolet-visible and Fourier transform infrared spectrometry. Based on the distinct fluorescence quenching of CdTe fluorescence probes in the presence of paracetamol, a simple, rapid and specific method for paracetamol determination was presented. Under optimum conditions, the relative fluorescence intensity of CdTe NPs was linearly proportional to paracetamol concentration from 1.0 × 10⁻⁸ mol/L to 1.6 × 10⁻⁷ mol/L with a detection limit of 4.2 × 10⁻⁹ mol/L. The proposed method was applied to detect paracetamol in commercial tablets with satisfactory results.     

Sonocatalytic degradation of EDTA in the presence of Ti and Ti@TiO2 nanoparticles

The sonocatalytic degradation of EDTA (C₀ = 5 10⁻³ M) in aqueous solutions was studied under 345 kHz (P_ac = 0.25 W mL⁻¹) ultrasound at 22–51 °C, Ar/20%O₂, Ar or air, and in the presence of metallic titanium (Ti⁰) or core-shell Ti@TiO₂ nanoparticles (NPs). Ti@TiO₂ NPs have been obtained using simultaneous action of hydrothermal conditions (100–214 °C, autogenic pressure P = 1.0–19.0 bar) and 20 kHz ultrasound, called sonohydrothermal (SHT) treatment, on Ti⁰ NPs in pure water. Ti⁰ is composed of quasi-spherical particles (30–150 nm) of metallic titanium coated with a metastable titanium suboxide Ti₃O. SHT treatment at 150–214 °C leads to the oxidation of Ti₃O and partial oxidation of Ti⁰ and formation of nanocrystalline shell (10–20 nm) composed of TiO₂ anatase. It was found that Ti⁰ NPs do not exhibit catalytic activity in the absence of ultrasound. Moreover, Ti⁰ NPs remain inactive under ultrasound in the absence of oxygen. However, significant acceleration of EDTA degradation was achieved during sonication in the presence of Ti⁰ NPs and Ar/20%O₂ gas mixture. Coating of Ti⁰ with TiO₂ nanocrystalline shell reduces sonocatalytic activity. Pristine TiO₂ anatase nanoparticles do not show a sonocatalytic activity in studied system. Suggested mechanism of EDTA sonocatalytic degradation involves two reaction pathways: (i) sonochemical oxidation of EDTA by OH/HO₂ radicals in solution and (ii) EDTA oxidation at the surface of Ti⁰ NPs in the presence of oxygen activated by cavitation event. Ultrasonic activation most probably occurs due to the local heating of Ti⁰/O₂ species at cavitation bubble/solution interface.     

Solvent effects on the linear and nonlinear optical response of silver nanoparticles

Linear and nonlinear (NL) optical properties of silver colloids stabilized with poly(N-vinylpyrrolidone) (PVP) in water, acetone, methanol, and ethylene glycol were studied. Images obtained by transmission electron microscopy reveal narrow size distributions of silver nanoparticles (NPs) with diameters centered at ≈ 6.3 nm (aqueous colloid) and in the 4.3–4.9 nm range for the other colloids. The behavior of the surface plasmon resonance band associated with the NPs was monitored through the linear absorption spectrum, and its dependence on the linear refraction index and the electric dipole moment (EDM) of the solvent molecules was analyzed. The phenomenological parameter, A, obtained from the linear absorption spectra, includes contributions due to the surface effects and the solvent. The third order susceptibility of the colloid was measured using the Z-scan technique at 532 nm, and the NL optical susceptibility of the NPs was determined using the Maxwell–Garnett model. The results indicate that the NL response of the colloids is largely influenced by the molecules adsorbed on the NPs surfaces and the EDM of the solvent molecules. PACS  42.65.-k; 42.65.An; 73.20.Mf; 78.67.-n; 78.67.Bf; 82.70.Dd     

Sonochemical synthesis of silver nanorods by reduction of sliver nitrate in aqueous solution

The sonochemical synthesis of sliver nanorods has been achieved by ultrasonic irradiation of the aqueous solution of sliver nitrate, methenamine (HMTA) and poly (vinyl pyrrolidone) (PVP) for 60 min. The silver nanorods obtained have lengths of 4–7 μm and mean diameters of about 100 nm. The structures of the samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and X-ray powder diffraction (XRD), and the chemical composition of the sample was examined by energy-dispersive X-ray spectrum (EDS). The effects of the irradiation time, the concentration of PVP and the reaction temperature on the morphology of silver nanorods were discussed, and the mechanism of the silver nanorods formation was tentatively inferred.     

表面增强拉曼光谱对鱼肉中组胺的快速定量分析

基于表面增强拉曼光谱（SERS）拟建立一种适用于水产鱼制品中组胺含量的快速检测方法。采用银纳米颗粒（Ag NPs）作为活性基底和氯化钠溶液作为聚集剂获取组胺的SERS特征峰,并结合线性回归算法对鱼肉中的组胺含量进行测定分析。首先对固体组胺、组胺水溶液以及鱼肉提取液中组胺的SERS特征峰及归属进行表征分析,然后对以Ag NPs的浓缩倍数与氯化钠溶液的浓度作为SERS基底的反应条件进行优化,最后在该优化条件下对鱼肉中组胺进行定量分析。结果表明,Ag NPs在400 nm处有最大吸光度,通过透射电子显微镜观察颗粒的形状主要为球形,均匀尺寸为30 nm左右。利用4-巯基苯甲酸作为探针分子对其进行拉曼测试,所得拉曼峰具有良好的重复性,且拉曼强度很高。因此该活性基底的合成方法不仅用时少、易操作,且合成的Ag NPs可作为可靠的增强基底应用于SERS试验中。此外通过紫外-可见分光光度计检测得出氯化钠溶液使Ag NPs在溶液中发生团聚,形成热点,可实现SERS信号增强。固体组胺的拉曼光谱图反映出1 167 cm-1处出现的特征峰主要是由N-H面内弯曲引起的;1 236 cm-1处的特征峰主要是咪唑中C-H平面内弯曲和环呼吸引起的;1 291 cm-1处主要与环伸展有关;1 474 cm-1处的特征峰主要是由咪唑N-H面内弯曲振动和环伸展引起的。优化反应条件在Ag NPs的浓缩倍数为15倍、氯化钠溶液浓度为1 mol·L-1时表现出最高的增强效应,并在该优化条件下检测了浓度为5～250 mg·L-1的组胺水溶液,得出在该优化条件下检测到组胺水溶液的最低浓度为5 mg·L-1。同时在该优化条件下采集了10～100 mg·L-1范围的鱼肉提取液中组胺的SERS光谱,并建立组胺溶液的特征拉曼位移峰强度与浓度之间的线性回归模型。得出在1 180,1 258和1 425 cm-1处的特征峰与对应的拉曼峰强度值所建立的标准曲线有良好的线性关系(R2=0.918 1～0.947 3),通过比较得出在1 258 cm-1处特征拉曼位移峰强度的R2值最大,且在鱼肉中组胺的最低检测浓度为10 mg·L-1, 远低于国标中水产品中组胺最大限量检测限50 mg·L-1。因此选择1 258 cm-1处的标准曲线进行进一步的组胺检测。最后通过对鱼肉提取液中添加组胺对该标准曲线进行检测验证,得到回收率在100%～111%之间。且通过高效液相色谱法验证该方法具有适用性。由此表明选取银纳米颗粒作为活性基底、氯化钠溶液作为聚集剂的表面增强拉曼光谱技术结合线性回归法建立标准曲线用于快速检测鱼肉中的组胺是可行且准确,这为在鱼肉中的组胺含量的快速定量分析提供了参考依据。     

Fabrication of silver nanoparticles in a continuous flow,low temperature microwave-assisted polyol process

The performed experiments showed that continuous microwave-assisted polyol synthesis at about 70 °C is a viable process to give silver nanoparticles with a narrow size distribution in bulk amounts. The increase of silver precursor concentration in reaction system from 0.0097 to 0.0389 M resulted in the formation of fine nanoparticles 5–10 nm in size, in addition to the larger ones 30–100 nm, and that changed the pattern of particle size distribution from monomodal to bimodal. The effect of specific process variables was found to be the same in the continuous process as in batch operation. An aqueous glycerol solution was found suitable for use as both solvent and reducing agent.     

Simple and environmentally friendly preparation and size control of silver nanoparticles using an inhomogeneous system with silver-containing glass powder

A simple, environmentally friendly method for preparing highly size-controlled spherical silver nanoparticles was developed that involved heating a mixture of silver-containing glass powder and an aqueous solution of glucose. The stabilizing agent for silver nanoparticles was found to be caramel, which was generated from glucose when preparing the nanoparticles. The particle size was independent of the reaction time, but it increased proportionally with the square root of the glucose concentration in the range 0.25–8.0 wt% (corresponding to particle sizes of 3.48 ± 1.83 to 20.0 ± 2.76 nm). Difference of the generation mechanism of silver nanoparticles between this inhomogeneous system and a system in which Ag⁺ was homogeneously dispersed was discussed.     

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 .     

绿色合成银纳米粒子及其在SERS中的应用

采用无毒、绿色的酪氨酸作为还原剂和稳定剂,在碱性条件下还原硝酸银,经60 ℃恒温水浴处理20 min,成功地合成了银纳米粒子。混合溶液颜色由淡黄色变为棕黄色直观地呈现了银纳米粒子的生成。利用紫外可见吸收光谱(UV-Vis)和透射电子显微镜(TEM)对制备样品进行分析和表征。粒子的UV-Vis吸收在412 nm附近。TEM图像显示,银纳米粒子的形状近似球形,粒子直径在15～25 nm。分别以结晶紫(CV)和叶酸(FA)为探测分子,进一步研究了该银纳米粒子的表面增强拉曼散射(SERS)效应。实验结果表明,该合成方法不仅方便、快速、绿色环保,而且合成的银纳米粒子对CV和FA分子有很好的SERS效应。     

Effect of temperature on the synthesis of silver nanoparticles with polyethylene glycol: new insights into the reduction mechanism

Polyethylene glycol (PEG) molecules act as a reducing and stabilizing agent in the formation of silver nanoparticles. PEG undergoes thermal oxidative degradation at temperatures over 70 °C in the presence of oxygen. Here, we studied how the temperature and an oxidizing atmosphere could affect the synthesis of silver nanoparticles with PEG. We tested different AgNO₃ concentrations for nanoparticles syntheses using PEG of low molecular weight, at 60 and 100 °C. At the higher temperature, the reducing action of PEG increased and the effect of PEG/Ag⁺ ratio on nanoparticles aggregation changed. These results suggest that different synthesis mechanisms operate at 60 and 100 °C. Thus, at 60 °C the reduction of silver ions can occur through the oxidation of the hydroxyl groups of PEG, as has been previously reported. We propose that the thermal oxidative degradation of PEG at 100 °C increases the number of both, functional groups and molecules that can reduce silver ions and stabilize silver nanoparticles. This degradation process could explain the enhancement of PEG reducing action observed by other authors when they increase the reaction temperature or use a PEG of higher molecular weight