Nonuniform Distribution of Capping Ligands Promoting Aggregation of Silver Nanoparticles for Use as a Substrate for SERS

Citrate-reduced silver nanoparticles (Ag-NPs) are used extensively for surface-enhanced Raman scattering (SERS) studies, but are typically found to aggregate using an aggregation agent. This study is aimed at developing a simple, stable, and reproducible aggregated method for Ag-NPs without any aggregation agents in aqueous solutions. The aggregation is induced by the process of centrifugation, water washing and ultrasonication. A mechanism based on the nonuniform distribution of capping ligands is proposed to account for the aggregated structure formation. UV-Vis-NIR extinction spectra and TEM allowed us to identify the existence of Ag-NPs aggregation. Further, due to the polydisperse mixture of Ag-NPs (20~65 nm) used in the present work, Ag-NPs are aggregated closely, which contribute to the observation of low-concentration SERS from the residual citrate layer or even the single-molecule SERS of R6Gon aggregation. After the evaporation of droplet of Ag-NPs aggregation on the Si substrate, citrate or R6Gcould also be detected but with marked redor blue-shifts.

Water chemistry controlled aggregation and photo-transformation of silver nanoparticles in environmental waters

The inevitable release of engineered silver nanoparticles（Ag NPs） into aquatic environments has drawn great concerns about its environmental toxicity and safety. Although aggregation and transformation play crucial roles in the transport and toxicity of Ag NPs, how the water chemistry of environmental waters influences the aggregation and transformation of engineered Ag NPs is still not well understood. In this study, the aggregation of polyvinylpyrrolidone（PVP） coated Ag NPs was investigated in eight typical environmental water samples（with different ionic strengths, hardness, and dissolved organic matter（DOM） concentrations） by using UV–visible spectroscopy and dynamic light scattering. Raman spectroscopy was applied to probe the interaction of DOM with the surface of Ag NPs. Further, the photo-transformation and morphology changes of Ag NPs in environmental waters were studied by UV–visible spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The results suggested that both electrolytes（especially Ca2＋and Mg2＋） and DOM in the surface waters are key parameters for Ag NP aggregation, and sunlight could accelerate the morphology change, aggregation, and further sedimentation of Ag NPs. This water chemistry controlled aggregation and photo-transformation should have significant environmental impacts on the transport and toxicity of Ag NPs in the aquatic environments.

Is there a silver lining? Aggregation and photo-transformation of silver nanoparticles in environmental waters

The nanotechnology industry advances rapidly,and at the vanguard are the promising silver nanoparticles（Ag NPs）,which have diverse applications.These nanometer-sized particles have been shown to inhibit the ability of bacteria to produce adenosine triphosphate（ATP）,a molecule necessary for chemical energy transport in cells.The antimicrobial properties of Ag NPs（and Ag＋）make them valued antibacterial

Influence of extracellular polymeric substances from activated sludge on the aggregation kinetics of silver and silver sulfide nanoparticles

Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.

Comparative Study of the Silver Nano-/Microstructures Deposited from Aerosol and Fog

A comparative study of the structure and fractal properties of arrays of the silver nano-/micro-particles deposited on the silicon substrate both from the aerosol and fog showed that the form of the silver individual particles and nano-/microstructures greatly depends on the deposition conditions. By passing an aerosol through isopropyl alcohol, the formation of fractal aggregates of the silver nano-/micro-particles both in the air and in alcohol was observed. Deposition of the silver nano-/micro-particles in the atmosphere of the saturated isopropyl alcohol vapours led to formation of fog. Microdroplets of the silver colloidal solution were deposited on the substrate. The further evaporation of alcohol created the silver nano/microstructures in the form of annular layers. It was found that the concerned annular layers contained silver particles of the same shape in the form of a Crescent (or Janus-nano-/microparticles). The nature of discovered effects is discussed.

在线性或交联的聚氨酯粒子内原位还原制备纳米银粒子

Linear or cross linked aqueous polyurethane dispersions with carboxyl Ag salt were prepared. TEM photos show that Ag + was homogeneously distributed in the microspheres. The Ag + was reduced in situ by photochemical method. For linear polyurethane particles, as the extent of the reduction reaction of silver ions increased, the silver particles grew larger, but the number of the silver particles kept almost constant. In crosslinked polymer system, the number of silver particles increased, but the size of silver particles remained almost the same. We concluded that nucleation and growth of the silver particle are the result of the silver atom movement in the polymer matrix. In the linear polymer system, the movement of silver atom and aggregation of silver particles result in the formation and growth of several silver particles; in the cross linked polymer system, the polymer chain prevents the movement of silver particles, resulting in a number increase of silver particles.

纳米银的电解质效应

向2种不同电性的纳米银溶胶中分别加入KCl、KBr、KI、KNO3、Mg(NO3)2、Al(NO3)3、K2CO3、K2SO4、KOH和HNO3电解质溶液,利用透射电子显微镜、紫外-可见分光光度计等研究电解质对纳米银的显微结构和光谱学性质的影响。结果表明,不同电解质离子在纳米银胶体表面吸附程度以及导致纳米银胶体聚集和生长程度不同,从而对纳米银胶体的分散状态和表面电势产生不同影响。这种影响的结果导致其对相同电性纳米银粒子和不同电性纳米银粒子的显微结构和光谱学性质影响不同。

纳米Ag在四种不同性质土壤上的吸附行为研究

纳米Ag的大量生产和使用增加了其进入土壤环境的风险,其在土壤中的环境行为受纳米Ag胶体稳定性和土壤理化性质的影响。为探究纳米Ag颗粒在土壤上的吸附行为,选取四种不同理化性质的土壤,考察了土壤p H、有机质和二价阳离子Ca2+对纳米Ag在土壤上吸附的影响。结果表明,纳米Ag在酸性土壤的吸附量高于中性土壤,当土壤酸碱性相似时土壤有机质含量越高纳米Ag在其表面的吸附量越高,纳米Ag在四种土壤上的吸附等温线都能较好地利用Freundlich方程进行拟合;Ca2+的存在均增加了纳米Ag在四种土壤上的吸附量,Ca2+浓度在0.1~10 mmol·L-1范围内,纳米Ag在中性土壤上的吸附量随Ca2+浓度的增加而增加,而在酸性土壤上则随着Ca2+浓度的增加,出现先增加后减小的趋势。这一结果有助于了解纳米银在不同性质土壤上的吸附行为,为评价纳米Ag在环境中的毒性和生态风险提供了有用信息。

基于未修饰银纳米粒子光度法测定卡托普利

研究建立了一种简单、快速、高灵敏测定药物卡托普利的新方法。该方法基于卡托普利诱导未修饰的银纳米粒子的快速团聚,从而使银纳米溶胶从亮黄色变为红色,在395nm处的吸光度呈线性降低。探讨了银纳米粒子的团聚机理。在优化条件下,该方法测定卡托普利的线性范围为1～35μg.mL-1,检出限为0.7μg.mL-1。应用于卡托普利药片含量的测定,获得了满意结果。

纳米银与微塑料在模拟垃圾填埋柱中的共迁移特征

以模拟垃圾填埋柱和人工配制渗滤液,探讨了纳米银(AgNPs)和微塑料(MPs)在垃圾填埋场中的迁移行为.结果发现,无论是单体系还是二元体系,随着填埋时间增长,AgNPs和MPs颗粒在渗滤液中稳定性增强,在填埋场中迁移能力增大,可能导致填埋中晚期有更多的污染颗粒随渗滤液流出填埋场.当AgNPs和MPs共存时,相对于单体系促进了AgNPs的迁移而轻微地抑制了MPs的迁移.结合DLVO理论和胶体过滤理论分析,一方面是由于流动性更高的MPs可作为AgNPs的载体,同时与AgNPs竞争固相介质上的吸附位点,从而促进AgNPs的迁移.另一方面,共存的AgNPs降低了MPs颗粒的表面负电荷使其稳定性减弱,并通过预沉积在固相介质上提供额外的MPs沉积位点,从而抑制MPs的迁移.

农产品中脱氧雪腐镰刀菌烯醇的表面增强拉曼检测

利用便携式拉曼光谱仪建立了一个快速筛查与检测谷物中真菌毒素脱氧雪腐镰刀菌烯醇(DON)的表面增强拉曼散射(SERS)方法。首先利用实验室前期开发的方法制备了具有高活性的水凝胶SERS芯片。该SERS芯片是将预先制备的高SERS活性的单层碳基点(CDs)包裹的银纳米颗粒团聚体(a-AgNPs/CDs)与聚乙烯醇(PVA)水溶液混合均匀后,再利用循环冷冻-解冻的物理交联法制备而成的。实验优化了影响水凝胶SERS芯片对DON的SERS响应的实验条件,包括溶剂、浸泡温度和浸泡时间。在最佳的SERS检测条件下(溶剂为水-乙醇(1∶1, v/v),浸泡温度为40℃,浸泡时间为5 min), DON的线性响应范围为1~10 000μg/kg(相关系数(R~2)=0.996 7),检出限(LOD)为0.14μg/kg,表明该SERS基底具有较高的灵敏度。得益于水凝胶特殊的孔径结构,实际样品基质中常见的糖、蛋白质、油脂、色素等干扰物质都被阻隔在水凝胶外。因此,在复杂样品检测中仅需要简单的提取,而不需要复杂的分离处理。将该方法用于小麦粉中DON的检测,所得回收率为97.3%~103%,相对标准偏差为4.2%~5.0%。实验结果表明所建立的检测DON的SERS方法具有响应范围宽、灵敏度高、重复性好、响应迅速、操作简单、抗干扰能力强等优点,这说明本实验室所构建的水凝胶SERS芯片在粮食中生物毒素的快速筛查与检测方面具有良好的应用潜力。

聚集效应对银纳米粒子的二阶非线性光学特性的影响研究

运用超瑞利散射 (HRS)技术 ,对由KNO3诱导聚集的银纳米粒子的二阶光学非线性特性进行了实验研究 .通过粒子尺寸测量和透射电镜观察 ,表明银纳米粒子的聚集方式为链状聚集 .当聚集体平均尺寸为 12 0nm时 ,银纳米粒子聚集体的HRS信号强度比聚集前增大了约 15倍 .分析表明 ,聚集导致银纳米粒子表面电场极化强度的增强和极化分布的改变 。