纳米银比色法检测多巴胺

在银纳米粒子存在下, 多巴胺可还原硝酸银生成银, 导致银纳米粒子粒径增大, 从而使溶液颜色发生改变. 基于此, 提出了一种用于检测多巴胺的纳米银比色法. 随着多巴胺浓度的增大, 溶液的颜色由浅黄色逐渐变为深黄色, 银纳米粒子溶液的吸收峰发生红移且吸光度增大. 在最优实验条件下, 该方法检测多巴胺的线性范围为0.05~16 μmol/L, 检出限为0.04 μmol/L. 该方法操作简单、 灵敏且选择性良好, 可用于人血清中多巴胺的检测.     

不同形态银纳米粒子的非线性光学特性

通过光诱导生长制备了三角形和圆盘形银纳米粒子, 并采用飞秒Z-scan技术考察了这2种形貌的银纳米粒子在800 nm光波长下的非线性光学特性. 在基态等离子漂白和自由载流子吸收等效应的作用下, 粒径为75 nm的三角形银纳米粒子的非线性透过率随激发光强的增加而呈现由饱和向反饱和非线性吸收过渡的现象; 粒径为35 nm的圆盘形银纳米粒子仅表现出反饱和吸收现象. 实验结果表明, 银纳米粒子非线性吸收过程受粒子形态调控.     

聚丙烯酰胺存在下微波高压合成银纳米粒子及其光谱特性

以聚丙烯酰胺为还原剂和稳定剂 ,采用微波高压液相合成法制备了黄色银纳米粒子。用吸收光谱和共振散射光谱研究了其制备条件的影响。在 4 2 1.6nm处产生最大吸收峰 ,在 4 70nm处产生一个最强共振散射峰。实验表明 :该法制备的银纳米粒子粒径均匀 ,平均粒径为 6 6nm ,其稳定性和分散性较好 ,合成方法简便、快捷。     

钯纳米微粒的微波高压液相合成及共振散射光谱研究

以柠檬酸钠作为制备钯纳米微粒晶种的还原剂,聚丙烯酰胺作为晶种生长的还原剂和稳定剂,采用微波高压液相合成法制备液相钯纳米粒子。TEM表明,钯纳米粒子呈球形,通过改变柠檬酸钠浓度可获得粒径为6－76nm的钯纳米粒子。柠檬酸在216nm处有一个吸收峰。聚丙烯酰胺在205nm处有一个吸收峰。钯纳米粒子体系在紫外可见光波长范围内无吸收峰,随着波长的降低其吸收增大。粒径为6－76nm的低浓度钯纳米粒子均在470nm、510nm、400nm、800nm和940nm产生五个共振散射峰。     

银纳米棱镜的形成及其光学性能研究

以有机溶剂作为反应介质,聚合物为稳定剂,通过微波辅助溶液法成功地制备了具有特殊光学性能的银纳米棱镜.利用X射线衍射、透射电子显微镜和紫外-可见光谱等手段跟踪反应过程.结果显示,随着反应的进行,银纳米粒子由10nm左右的球形颗粒逐渐转变为具有规则三角形(或缺角的三角形)形貌的纳米棱镜;同时,紫外-可见吸收峰不但显示出明显的量子尺寸效应,而且吸收峰也由单一的等离子共振吸收峰变为多重的多极吸收峰共同存在,胶体溶液也随之显示出不同的颜色.改变反应物的配比、体系的浓度及无机前驱物都会得到位置和峰形各不相同的吸收曲线,从而得到多彩的纳米银胶体溶液.     

Preparation and Storage of Silver Nanoparticles in Aqueons Polymers

以水溶性聚合物为保护剂,采用化学还原法制备了银纳米粒子,分别利用透射电子显微镜、紫外可见光谱、同步光散射光谱等手段对其进行了表征,并探索了制备银纳米粒子的最佳实验条件。通过将银纳米粒子-聚合物溶液进行脱水,得到含有银纳米粒子的固态聚合物膜。将固态聚合物膜重新溶解于水,其水溶液的紫外可见光谱与脱水前的溶液进行了比较,发现两者性质并无明显差异。因此,将银纳米粒子分散固定在聚合物膜中是一种崭新而有效的银纳米粒子制备和存储方法。     

紫外光照射制备具有光学活性的银纳米粒子

以脱氧胆酸钠(NaDC)为还原剂、稳定剂,经紫外光辐照AgNO3溶液在室温下制备出尺寸30 nm左右的类球形的银纳米粒子。用紫外-可见光谱、透射电镜、圆二色谱和傅立叶变换红外光谱等测试手段对所制备的脱氧胆酸钠包裹的银纳米粒子进行了表征。红外光谱结果表明,在紫外光激发下,脱氧胆酸钠甾环上12α-OH发生氧化反应,同时还原Ag+为单质银,并聚集生成银纳米粒子。溶液的pH值对光化学氧化还原反应速度有着重要的影响,增加溶液的pH值,Ag+的还原反应速度明显加快。在吸附在银粒子表面的脱氧胆酸钠的手性氛围诱导下,生成的银纳米粒子在其表面等离子体共振区域出现手性信号。     

CeO2@Au核壳结构纳米粒子的合成与性质研究

采用沉淀法制备了球形CeO2纳米粒子,将其作为核粒子溶液,然后向其中滴加四氯合金酸溶液,在CeO2胶体表面利用柠檬酸钠还原[AuCl4]-离子,得到了CeO2@Au核壳结构纳米粒子。TEM分析表明,CeO2纳米粒子分散效果好,粒径为5 nm;CeO2@Au核壳粒子为球形,无团聚,平均粒径为15 nm。XRD分析表明,CeO2@Au核壳粒子为晶型结构,属于立方晶系,CeO2空间群为O5H-FM3M,Au的空间群为Fm-3m。UV-vis分析发现,CeO2@Au核壳粒子在300和520 nm处呈现出两个比较强的吸收峰,分别对应于CeO2胶体溶液的吸收峰和金粒子的表面等离子共振吸收峰。EDS分析了核壳结构CeO2@Au纳米粒子中存在Ce,O和Au 3种元素。XPS分析表明,Ce3d3/2和Au4f电子结合能与标准结合能相比发生了变化,说明CeO2与Au之间存在着相互作用。     

Ag-PVA和Ag-PVA/TiO2复合超薄膜的制备及性能研究

用3种方法制备了银纳米粒子-聚乙烯醇复合体系,其中用加热还原法所得体系中Ag纳米粒子的尺寸较大(15nm),其表面等离子体共振吸收峰较宽,最大吸收波长位于420nm;用室温硼氢化钠还原法得到的复合体系的吸收峰蓝移至409nm,且峰形较窄,Ag纳米粒子的平均粒径为8.7nm;低温NaBH4还原法所得体系吸收峰进一步蓝移至397nm,此时Ag纳米粒子粒径最小(3.5nm).将室温还原法所得Ag-PVA复合体系旋涂成膜,所得薄膜光滑、透明、均匀性好,该法适用于制备多层薄膜,以调控薄膜的厚度和光谱性质.将Ag-PVA复合体系与钛酸四丁酯(Ti(O_nBu)₄)的乙醇溶液交替旋涂得到Ag-PVA/TiO₂有机/无机复合薄膜.紫外-可见吸收光谱研究表明,随着Ag-PVA层数的增加,薄膜的表面等离子体共振吸收强度呈线性增加,但是TiO₂层数的增加对吸收光谱没有明显影响.Ag-PVA/TiO₂有机/无机复合薄膜将金属纳米粒子、有机高分子与无机半导体材料结合在一起,这种多层纳米结构在光电、催化功能薄膜等方面具有潜在的应用前景.     

绿色银纳米粒子的共振散射光谱研究

以柠檬酸钠作光还原剂,采用紫外光-可见光二步光化学法制备了绿色银纳米离子,在399.4nm和691.5nm处有二个紫外-可见吸收峰;在340nm,470nm和520nm处有三个共振散射峰,从超分子和纳米粒子这一整体出发,探讨了共振散射光谱产生的原因及银超分子光反应机理。     

One-step synthesis of monodisperse silver nanoparticles beneath vitamin E Langmuir monolayers

The monodisperse silver nanoparticles were synthesized by one-step reduction of silver ions in the alkaline subphase beneath vitamin E (VE) Langmuir monolayers. The monolayers and silver nanocomposite LB films were characterized by surface pressure-area (pi-A) isotherms, transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), selected area electron diffraction (SAED), Fourier transform infrared transmission spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that the limiting area/VE molecule on different subphases varied. The phenolic groups in the VE molecules were converted to a quinone structure, and the silver ions were mainly reduced to ellipsoidal and spherical nanoparticles. The arrangement of the nanoparticles changed from sparseness to compactness with reaction time. The electron diffraction pattern indicated that the silver nanoparticles were face-centered cubic (fcc) polycrystalline. Silver nanocomposite LB films with excellent quality could be formed on different substrates, indicating that the transfer ratio of monolayer containing silver nanoparticles is close to unity. The dynamic process of reduction of silver ions by VE LB films was also studied through monitoring the conductivity of an Ag2SO4 alkaline solution.     

Biosynthesis of silver nanocrystals by Bacillus licheniformis

The use of microorganisms for the synthesis of nanoparticles is in the limelight of modern nanotechnology. Using the bacterium Bacillus licheniformis, the biosynthesis of silver nanoparticles was investigated. These silver nanoparticles were characterized by means of UV-vis spectroscopy, scanning electron microscopy (SEM), electron diffraction spectroscopy (EDX) and X-ray diffraction (XRD). The nanoparticles exhibited maximum absorbance at 440 nm in UV-vis spectroscopy. The XRD spectrum of silver nanoparticles exhibited 2theta values corresponding to the silver nanocrystal. SEM micrographs revealed the formation of well-dispersed silver nanoparticles of 50 nm, and the presence of silver was confirmed by EDX analysis.     

Preparation, characterization, and optical properties of gold, silver, and gold-silver alloy nanoshells having silica cores

This report describes the structural and optical properties of a series of spherical shell/core nanoparticles in which the shell is comprised of a thin layer of gold, silver, or gold-silver alloy, and the core is comprised of a monodispersed silica nanoparticle. The silica core particles were prepared using the St?ber method, functionalized with terminal amine groups, and then seeded with small gold nanoparticles (approximately 2 nm in diameter). The gold-seeded silica particles were coated with a layer of gold, silver, or gold-silver alloy via solution-phase reduction of an appropriate metal ion or mixture of metal ions. The size, morphology, and elemental composition of the composite nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The optical properties of the nanoparticles were analyzed by UV-vis spectroscopy, which showed strong absorptions ranging from 400 nm into the near-IR region, where the position of the plasmon band reflected not only the thickness of the metal shell, but also the nature of the metal comprising the shell. Importantly, the results demonstrate a new strategy for tuning the position of the plasmon resonance without having to vary the core diameter or the shell thickness.     

Green synthesis of silver nanoparticles for ammonia sensing

Silver nanoparticles synthesized by a reagent less method involving only UV radiation have been used in colorimetric assay for the detection of ammonia in solution. The silver nanoparticles were synthesized by the exposure of a silver nitrate solution to a low-power UV source in the presence of poly(methacrylic acid) (PMA), which acted both as reducing and capping agent. The synthesis of the silver nanoparticles was studied by monitoring the changes in position and amplitude of the localized plasmon resonance (LSPR) band using UV-vis spectroscopy. The morphology of the particles was studied using transmission electron microscopy which confirmed the formation of spherical particles with an average particle size around 8 nm. Interestingly, the silver nanoparticles solution was found to display a strong color shift from purple to yellow upon mixing with increasing concentration of ammonia ranging from 5 to 100 ppm. Hence, the nanoparticles prepared with this method could be used as colorimetric assay for sensing applications of ammonia in water.     

Preparation of Silver Nanoparticles through Alcohol Reduction with Organoalkoxysilanes

Silver nanoparticles of narrow size distribution were prepared through the chemical reduction in an alcohol solution with several organoalkoxysilanes. In this system, organoalkoxysilanes served as a stabilizer, protecting silver nanoparticles from aggregation. The changes in size and morphology of colloidal silver nanoparticles were investigated with the addition of organoalkoxysilanes such as 3-aminopropyltriethoxysilane (APS), methyltriethoxysilane (MTS), phenyltrimethoxysilane (PTS), vinyltriethoxysilane (VTS), and 3-glycidoxypropyltrimethoxysilane (GPS) as stabilizers. The organic functional groups of organoalkoxysilanes interact with silver ions and clusters, which stabilize silver nanoparticles in the system. The silver nanoparticles obtained were characterized with transmission electron microscopy (TEM), UV-vis spectroscopy, etc.     

Role of phenol derivatives in the formation of silver nanoparticles

We demonstrate that dihydroxy benzenes are excellent reducing agents and may be used to reduce silver ions to synthesize stable silver nanoparticles in air-saturated aqueous solutions. The formation of Ag nanoparticles in deaerated aqueous solution at high pH values suggests that the reduction of silver ions occurs due to oxidation of dihydroxy benzenes and probably on the surface of Ag2O. Pulse radiolysis studies show that the semi-quinone radical does not participate in the reduction of silver ions at short time scales. Nevertheless, results show that primary intermediates undergo slower transformation in the presence of dihydroxy benzenes than in their absence. This slow transformation eventually leads to the formation of silver nanoparticles. The Ag nanoparticles were characterized by UV-vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and TEM techniques showed the presence of Ag nanoparticles with an average size of 30 nm.     

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.     

Green biosynthesis of silver nanoparticles using Callicarpa maingayi stem bark extraction

Different biological methods are gaining recognition for the production of silver nanoparticles (Ag-NPs) due to their multiple applications. The use of plants in the green synthesis of nanoparticles emerges as a cost effective and eco-friendly approach. In this study the green biosynthesis of silver nanoparticles using Callicarpa maingayi stem bark extract has been reported. Characterizations of nanoparticles were done using different methods, which include; ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDXF) spectrometry, zeta potential measurements and Fourier transform infrared (FT-IR) spectroscopy. UV-visible spectrum of the aqueous medium containing silver nanoparticles showed absorption peak at around 456 nm. The TEM study showed that mean diameter and standard deviation for the formation of silver nanoparticles were 12.40 ± 3.27 nm. The XRD study showed that the particles are crystalline in nature, with a face centered cubic (fcc) structure. The most needed outcome of this work will be the development of value added products from Callicarpa maingayi for biomedical and nanotechnology based industries.     

Extracellular biosynthesis of functionalized silver nanoparticles by strains of Cladosporium cladosporioides fungus

In the present investigation, we report the extracellular biosynthesis of silver nanoparticles (AgNP) employing the fungus Cladosporium cladosporioides. The extracellular solution of C. cladosporioides was used for the reduction of AgNO(3) solution to AgNP. The present study includes time dependent formation of AgNP employing UV-vis spectrophotometer, size and morphology by employing TEM (transmission electron microscopy), structure from powder X-ray diffraction (XRD) technique and understanding of protein-AgNP interaction from Fourier transform infrared (FT-IR) spectroscopy. The AgNP were 10-100nm in dimensions as measured by TEM images.     

Microwave-Assisted Coating of PMMA beads by silver nanoparticles

Microwave (MW) irradiation was found to be a new technique for coating silver nanoparticles with an average size of approximately 31 nm onto the surface of poly(methyl methacrylate) PMMA beads (3 mm diameter). The microwave polyol reduction was carried out under an argon atmosphere. Silver nanoparticles were obtained by the MW irradiation of a solution mixture containing silver nitrate (or silver acetate), poly(ethylene glycol), ethanol, water, and 24 wt % aqueous ammonia for 5 min in the presence of PMMA beads, yielding a PMMA-nanosilver composite. By controlling the atmosphere and reaction conditions, we could achieve the deposition of silver nanoparticles onto the surface of poly(methyl methacrylate) and vary the amount of the silver anchored to the surface. The resulting silver-deposited PMMA samples were characterized using X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, and volumetric titration with potassium thiocyanate (KSCN) according to the Folgard method.