以SDS-PEG团簇为软模板在温和条件下合成金纳米环

介绍一种由十二烷基硫酸钠(SDS)与聚乙二醇(PEG 20000)组成的团簇为软模板, 在室温、常压、无硬模板及无外加还原剂条件下自还原HAuCl₄合成金纳米环的新方法. TEM显示合成的金纳米环的直径为(500±50) nm; UV-vis光谱显示在800 nm以上区域有强吸收带, 证明有大的各向异性的纳米结构生成. 电子衍射(ED)显示合成的金纳米环为金单晶结构; XRD显示金纳米环的(200)与(111)衍射峰的强度比(I₍₂₀₀₎/I₍₁₁₁₎)为0.11, 比反应初始阶段的0.31降低0.2左右, 表明金纳米结构主要为(111)晶面取向. TEM和SEM跟踪显示, 金纳米环的生长经历了从金纳米球到纳米片再到纳米环的变化过程, 控制反应时间可以得到预期的金纳米结构.     

Plasmonic Pollen Grain Nanostructures: A Three-Dimensional Surface-Enhanced Raman Scattering (SERS)-Active Substrate

A new route has been developed to design plasmonic pollen grain-like nanostructures (PGNSs) as surface-enhanced Raman scattering (SERS)-active substrate. The nanostructures consisting of silver (Ag) and gold (Au) nanoparticles along with zinc oxide (ZnO) nanoclusters as spacers were found highly SERS-active. The morphology of PGNSs and those obtained in the intermediate stage along with each elemental evolution has been investigated by a high-resolution field emission scanning electron microscopy. The optical band gaps and crystal structure have been identified by UV-vis absorption and X-ray powder diffraction (XRD) measurements, respectively. For PGNSs specimen, three distinct absorption bands related to constituent elements Ag, Au, and ZnO were observed, whereas XRD peaks confirmed the existence of Ag, Au, and ZnO within the composition of PGNSs. SERS-activity of PGNSs was confirmed using Rhodamine 6G (R6G) as Raman-active dyes. Air-cooled solid-state laser kits of 532 nm were used as excitation sources in SERS measurements. SERS enhancement factor was estimated for PGNSs specimen and was found as high as 3.5×10⁶. Finite difference time domain analysis was carried out to correlate the electromagnetic (EM) near-field distributions with the experiment results achieved under this investigation. EM near-field distributions at different planes were extracted for s-, p- and 45° of incident polarizations. EM near-field distributions for such nanostructures as well as current density distributions under different circumstances were demonstrated and plausible scenarios were elucidated given SERS enhancements. Such generic fabrication route as well as correlated investigation is not only indispensable to realize the potential of SERS applications but also unveil the underneath plasmonic characteristics of complex SERS-active nanostructures.     

Synthesis of p-aminothiophenol-embedded gold/silver core-shell nanostructures as novel SERS tags for biosensing applications

We describe a novel surface-enhanced Raman scattering (SERS) tag that is based on Au/Ag core-shell nanostructures embedded with p-aminothiophenol. The Au/Ag core-shell sandwich nanostructures demonstrate bright and dark stripe structure and possess very strong SERS activity. Under optimum conditions, the maximum SERS signal was obtained with a 10?nm thick Ag nanoshell, and the enhancement factor is 3.4?×?10⁴ at 1077?cm^?1. After conjugation to the antibody of muramidase releasing protein (MRP), the Au/Ag core-shell nanostructures were successfully applied to an SERS-based detection scheme for MRP based on a sandwich type of immunoassay.

有序Au/Ag纳米碗阵列的简易制备及其表面增强拉曼散射性能

通过湿法化学合成基于SiO₂胶体晶体的大面积有序Au/Ag纳米碗(Au/AgNB)阵列。首先,在玻璃基板上组装3D SiO₂胶体晶体作为模板。然后,以Au纳米颗粒(AuNP)为种子,通过原位生长法在SiO₂模板上沉积一层Au纳米壳(AuNS)。再通过HCHO还原Ag⁺成Ag⁰,进一步在AuNS表面沉积Ag纳米壳,形成Ag/Au双纳米壳(Ag/AuNS)阵列。最后通过丙烯酸酯改性双向取向聚丙烯(BOPP)膜方便地获得了单层有序反转Ag/AuNB阵列。这种有序Au/AgNB阵列具有更佳的表面增强拉曼散射(SERS)活性,其SERS分析增强因子(AEF)可达2.23×10⁷。     

磁性Fe_2O_3/Au/Ag复合纳米粒子的制备及其富集作用研究

利用种子生长法制备了磁性Fe2O3/Au/Ag复合纳米粒子,采用UV-vis和SEM对其光学性质以及表面结构的变化进行了表征.通过调节硝酸银的用量,制备了一系列具有不同Ag壳层厚度和表面结构的双金属外壳纳米粒子.以苯硫酚(TP)为探针分子,研究了不同Ag壳厚度的磁性纳米粒子的表面增强拉曼散射(SERS)活性.结果表明其SERS活性与表面结构的改变有关,在同时出现Ag和Au光学性质的Fe2O3/Au/Ag复合纳米粒子表面可观察到最强的SERS效应,这与表面的针孔效应以及Ag和Au之间的耦合增强作用有关.考察了Fe2O3/Au/Ag复合纳米粒子的磁富集作用,并利用SERS原位监测磁富集溶液中低浓度TP的能力,研究结果表明通过磁富集可提高SERS检测限,并且Fe2O3/Au/Ag的磁富集能力较Fe2O3/Au弱,但前者SERS信号较强.     

First Principles Calculations Toward Understanding SERS of 2,2′-Bipyridyl Adsorbed on Au,Ag, and Au–Ag Nanoalloy

First principles electrodyanmics and quantum chemical simulations are performed to gain insights into the underlying mechanisms of the surface enhanced Raman spectra of 22BPY adsorbed on pure Au and Ag as well as on Au–Ag alloy nanodiscs. Experimental SERS spectra from Au and Ag nanodiscs show similar peaks, whereas those from Au–Ag alloy reveal new spectral features. The physical enhancement factors due to surface nano-texture were considered by numerical FDTD simulations of light intensity distribution for the nano-textured Au, Ag, and Au–Ag alloy and compared with experimental results. For the chemical insights of the enhancement, the DFT calculations with the dispersion interaction were performed using Au₂₀, Ag₂₀, and Au₁₀Ag₁₀ clusters of a pyramidal structure for SERS modeling. Binding of 22BPY to the clusters was simulated by considering possible arrangements of vertex and planar physical as well as chemical adsorption models. The DFT results indicate that 22BPY prefers a coplanar adsorption on a (111) face with trans-conformation having close energy difference to cis-conformation. Binding to pure Au cluster is stronger than to pure Ag or Au–Ag alloy clusters and adsorption onto the alloy surface can deform the surface. The computed Raman spectra are compared with experimental data and assignments for pure Au and Ag models are well matching, indicating the need of dispersion interaction to reproduce strong Raman signal at around 800 cm^–1. This work provides insight into 3D character of SERS on nanorough surfaces due to different binding energies and bond length of nanoalloys. © 2018 Wiley Periodicals, Inc.     

Rapid Synthesis of Hollow Ag–Au Nanodendrites in 15 Seconds by Combining Galvanic Replacement and Precursor Reduction Reactions

Metallic nanomaterials displaying hollow interiors as well as sharp tips/branches at their surface (such as hollow nanodendrites) are attractive, because these features enable higher surface‐to‐volume ratios than their solid and/or rounded counterparts. This paper describes a simple strategy for the synthesis of Ag–Au nanodendrites in 15 s using Ag nanospheres prepared in a previous synthetic step as seeds. Our approach was based on the utilization of Ag nanospheres as seeds for Au deposition by a combination of galvanic replacement reaction between Ag and AuCl₄^?(aq) and AuCl₄^?(aq) reduction using hydroquinone in the presence of polyvinylpyrrolidone (PVP) as a stabilizer and water as the solvent. The produced Ag–Au nanodendrites presented monodisperse sizes, and their surface morphologies could be tuned as a function of growth time. Owing to their hollow interiors and sharp tips, the Ag–Au nanodendrites performed as effective substrates for surface‐enhanced Raman scattering (SERS) detection of 4‐MPy (4‐mercaptopyridine) and R6G (rhodamine 6G) as probe molecules. We believe that the approach described herein can serve as a protocol for the fast and one‐step synthesis of Ag–Au hollow nanondendrites with a wide range of sizes, compositions, and surface morphologies for applications in SERS and catalysis.     

Silver overlayer-modified surface-enhanced Raman scattering-active gold substrates for potential applications in trace detection of biochemical species

Because Ag and Au nanoparticles (NPs) possess well-defined localized surface plasmon resonance (LSPR) they are popularly employed in the studies of surface-enhanced Raman scattering (SERS). As shown in the literature and in our previous studies, the advantage of SERS-active Ag NPs is their higher SERS enhancement over Au NPs. On the other hand, the disadvantage of SERS-active Ag NPs compared to Au NPs is their serious decay of SERS enhancement in ambient laboratory air. In this work, we develop a new strategy for preparing highly SERS-active Ag NPs deposited on a roughened Au substrate. This strategy is derived from the modification of electrochemical underpotential deposition (UPD) of metals. The coverage of Ag NPs on the roughened Au substrate can be as high as 0.95. Experimental results indicate that the SERS of Rhodamine 6G (R6G) observed on this developed substrate exhibits a higher intensity by ca. 50-fold of magnitude, as compared with that of R6G observed on the substrate without the deposition of Ag NPs. The limit of detection (LOD) for R6G measured on this substrate is markedly reduced to 2 × 10⁻¹⁵ M. Moreover, aging of SERS effect observed on this developed substrate is significantly depressed, as compared with that observed on a generally prepared SERS-active Ag substrate. These aging tests were performed in an atmosphere of 50% relative humidity (RH) and 20% (v/v) O₂ at 30 °C for 60 day. Also, the developed SERS-active substrate enables it practically applicable in the trace detection of monosodium urate (MSU)-containing solution in gouty arthritis without a further purification process.     

Fabrication of bimetallic microfluidic surface-enhanced Raman scattering sensors on paper by screen printing

Au–Ag bimetallic microfluidic, dumbbell-shaped, surface enhanced Raman scattering (SERS) sensors were fabricated on cellulose paper by screen printing. These printed sensors rely on a sample droplet injection zone, and a SERS detection zone at either end of the dumbbell motif, fabricated by printing silver nanoparticles (Ag NPs) and gold nanoparticles (Au NPs) successively with microscale precision. The microfluidic channel was patterned using an insulating ink to connect these two zones and form a hydrophobic circuit. Owing to capillary action of paper in the millimeter-sized channels, the sensor could enable self-filtering of fluids to remove suspended particles within wastewater without pumping. This sensor also allows sensitive SERS detection, due to advantageous combination of the strong surface enhancement of Ag NPs and excellent chemical stability of Au NPs. The SERS performance of the sensors was investigated by employing the probe rhodamine 6G, a limit of detection (LOD) of 1.1 × 10⁻¹³ M and an enhancement factor of 8.6 × 10⁶ could be achieved. Moreover, the dumbbell-shaped bimetallic sensors exhibited good stability with SERS performance being maintained over 14 weeks in air, and high reproducibility with less than 15% variation in spot-to-spot SERS intensity. Using these dumbbell-shaped bimetallic sensors, substituted aromatic pollutants in wastewater samples could be quantitatively analyzed, which demonstrated their excellent capability for rapid trace pollutant detection in wastewater samples in the field without pre-separation.     

Selective dissolution of the silver component in colloidal Au and Ag multilayers: a facile way to prepare nanoporous gold film materials

Colloidal Au/Ag multilayer films were prepared by alternate assembly of Au nanoparticles with a size of 5 +/- 1.2 nm and Ag nanoparticles with a size of 10 +/- 2.4 nm by using 1,5-pentanedithiol as cross-linker. Nanoporous gold films with a ligament size of 26.7 +/- 4.6 nm were then prepared by selective dissolution of sacrificial templates of silver particles in colloidal Au/Ag multilayers. The complete dissolution of Ag particles in colloidal Au/Ag multilayers in a mixture solution of 3.0 mM HAuCl(4) and 3 M NaCl took place at room temperature without damage of the colloidal Au film. This method to prepare nanoporous gold films was further extended to the preparation of nanoporous gold nanotubes by depositing colloidal Au/Ag film on the inner wall of anodic aluminum oxides (AAO) followed by dissolution of colloidal Ag and removal of AAO templates.     

Synthesis of highly-branched Au@AgPd core/shell nanoflowers for in situ SERS monitoring of catalytic reactions

Alloy and small size nanostructures are favorable to catalytical performance, but not to surface-enhanced Raman spectroscopy (SERS) applications. Integrating SERS and catalytic activity into the nanocrystals with both alloy and small size structures is of great interest in fabrication of SERS platform to in situ monitor catalytical reaction. Herein, we report a facile method to synthesize Au@AgPd trimetallic nanoflowers (Au@AgPd NFs) with both SERS and catalytic activities, through simultaneous selective growth of Ag and Pd on Au core to form highly-branched alloy shell. These nanocrystals have the properties of small sizes, defects abundance, and highly-dispersed alloy shell which offer superior catalytic activity, while the merits of monodisperse, excellent stability, and highly-branched shell and core/alloy-shell structure promise the enhanced SERS activity. We further studied their growth mechanisms, and found that the ratio of Ag to Pd, sizes of Au core, and surfactant cetyltrimethylammonium bromide together determine this special structure. Using this as-synthesized nanocrystals, a monolayer bifunctional platform with both SERS and catalytical activity was fabricated through self-assembly at air/water interface, and applied to in situ SERS monitoring the reaction process of Pd-catalyzed hydrogenation of 4-nitrothiophenol to 4-aminothiophenol.     

Dealloying Ag–Al Alloy to Prepare Nanoporous Silver as a Substrate for Surface‐Enhanced Raman Scattering: Effects of Structural Evolution and Surface Modification

Sensitive detection of molecules by using the surface‐enhanced Raman scattering (SERS) technique depends on the nanostructured metallic substrate and many efforts have been devoted to the preparation of SERS substrates with high sensitivity, stability, and reproducibility. Herein, we report on the fabrication of stable monolithic nanoporous silver (NPS) by chemical dealloying of Ag–Al precursor alloys with an emphasis on the effect of structural evolution on SERS signals. It was found that the dealloying conditions had great influence on the morphology (the ligament/pore size) and the crystallization status, which determined the SERS signal of rhodamine 6G on the NPS. NPS with small pores, low residual Al, and perfect crystallization gave high SERS signals. A high enhancement factor of 7.5×10⁵ was observed on bare NPS obtained by dealloying Ag₃₀Al₇₀ in 2.5 wt % HCl at room temperature followed by 15 min aging at around 85 °C. After coating Ag nanoparticles on the NPS surface, the enhancement factor increased to 1.6×10⁸ owing to strong near‐field coupling between the ligaments and nanoparticles.     

Heteropolymetallic Architectures as Snapshots of Transmetallation Processes at Different Degrees of Transfer

Novel heteropolymetallic architectures have been built by integrating Pd, Au and Ag systems. The dinuclear [(CNC)(PPh₃)Pd-^G11M(PPh₃)](ClO₄) (^G11M=Au ( 3 ), Ag ( 4 ); CNC=2,6-diphenylpyridinate) and trinuclear [{(CNC)(PPh₃)Pd}₂^G11M](ClO₄) (^G11M=Au ( 6 ), Ag ( 5 )) complexes have been accessed or isolated. Structural and DFT characterization unveil striking interactions of one of the aryl groups of the CNC ligand(s) with the ^G11M center, suggesting these complexes constitute models of transmetallation processes. Further analyses allow to qualitatively order the degree of transfer, proving that Au promotes the highest one and also that Pd systems favor higher degrees than Pt. Consistently, Energy Decomposition Analysis calculations show that the interaction energies follow the order Pd−Au > Pt−Au > Pd−Ag > Pt−Ag. All these results offer potentially useful ideas for the design of bimetallic catalytic systems.     

有序Au/Ag纳米碗阵列的简易制备及其表面增强拉曼散射性能

通过湿法化学合成基于SiO₂胶体晶体的大面积有序Au/Ag纳米碗(Au/AgNB)阵列。首先,在玻璃基板上以3D SiO₂胶体晶体作为模板。然后,在Au纳米颗粒(AuNP)种子的帮助下,通过原位生长方法在模板上沉积一层Au纳米壳(AuNS)。再通过HCHO还原Ag⁺使AuNS表面进一步沉积Ag纳米壳,形成Ag/Au双纳米壳(Ag/AuNS)阵列。通过丙烯酸酯改性双向取向聚丙烯(BOPP)方便地获得了单层有序反转Ag/AuNB阵列。这种有序Au/AgNB阵列具有更佳的表面增强拉曼散射(SERS)活性,其SERS分析增强因子(AEF)可达2.23×10⁷。     

Self‐Assembled Au Nanoparticles as Substrates for Surface‐Enhanced Vibrational Spectroscopy: Optimization and Electrochemical Stability

Three‐dimensional nanostructured metallic substrates for enhanced vibrational spectroscopy are fabricated by self‐assembly. Nanostructures consisting of one to 20 depositions of 13 nm‐diameter Au nanoparticles (NPs) on Au films are prepared and characterized by means of AFM and UV/Vis reflection–absorption spectroscopy. Surface‐enhanced polarization modulation infrared reflection–absorption spectroscopy (PM‐IRRAS) is observed from Au NPs modified by the probe molecule 4‐hydroxythiophenol. The limitation of this kind of substrate for surface‐enhanced PM‐IRRAS is discussed. The surface‐enhanced Raman scattering (SERS) from the same probe molecule is also observed and the effect of the number of Au‐NP depositions on the SERS efficiency is studied. The SERS signal from the probe molecule maximizes after 11 Au‐NP depositions, and the absolute SERS intensities from different batches are reproducible within 20 %. In situ electrochemical SERS measurements show that these substrates are stable within the potential window between ?800 and +200 mV (vs. Ag/AgCl/sat. Cl^?).     

银/金纳米线阵列表面增强拉曼基底的制备及对孔雀石绿的高灵敏度检测

利用种子介导的软模板生长方法制备了金纳米线(Au NWs)阵列, 通过调节生长温度控制Au NWs阵列的形貌, 最后在经硼氢化钠(NaBH₄)清洗过的Au NWs阵列上化学沉积银纳米颗粒(Ag NPs), 制得银/金纳米线(Ag/Au NWs)阵列作为表面增强拉曼散射(SERS)基底. 选用罗丹明6G(R6G)作为拉曼探针分子测定了Ag/Au NWs阵列的SERS性能. 结果表明, Ag/Au NWs阵列作为SERS基底具有高灵敏度、 优异的信号均匀性和良好的稳定性. 使用Ag/Au NWs阵列对孔雀石绿(MG)检测的检出限可低至1×10^-8 mol/L, 线性范围为 1×10^-8~1×10^-4 mol/L. NaBH₄可以在不影响SERS性能的情况下去除Ag/Au NWs阵列上吸附的分子, 使得 SERS基底可以重复使用. 使用Ag/Au NWs阵列对湖水中的MG进行检测, 得到了可靠的回收率, 证明Ag/Au NWs 阵列在检测环境水体中的孔雀石绿上具有应用潜力.     

Near-field and far-field scattering by bimetallic nanoshell systems

We have studied theoretically the far- and near-field scattering response of bimetallic Ag/Au core-shell and alloy nanoparticles. Particular emphasis is put on the near-field study, which is known to play a fundamental role in surface enhanced spectroscopies. The comparison between the scattering spectra of core-shell and alloy particles shows that for particles with a Au/Ag volume ratio greater than 2, the structural difference does not imply any significant difference in the optical response. For such particles, while the retardation effects are not negligible, the scattering at the interface between the two metals in the core-shell case does not seem to modify the scattering behavior. The scattering at the interface is conversely not negligible for particles with a lower Au/Ag ratio, where the particle inner structure seems to be important.     

Synthesis, characterization and SERS activity of Au-Ag nanorods

The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au(100-x)-Ag(x) particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au(80)-Ag(20) colloid consists of alloy nanorods with dimension of 25nmx100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.     

ZnO纳米环的可控合成

以六次甲基四胺(Hexamethylenetetramine, C6H12N4)和水合硝酸锌[Zn(NO3)2·2H2O]为原料, 表面活性剂聚丙烯酰胺-氯化二烯丙基二甲基铵[poly(acrylamide-co-diallyldimethylammonium chloride, 缩写为PAM-CTAC]为形貌控制剂, 采用液相沉淀法合成了ZnO纳米环. 产物的结构与形貌经X射线粉末衍射(XRD)和扫描电子显微镜(SEM)表征. 研究了不同实验条件(如表面活性剂的浓度、反应物浓度、反应温度和反应时间等)对产物形貌与尺寸的影响. 讨论了PAM-CTAC作用下ZnO纳米环可能的形成机理. 结果表明, 合成产物为六方Wurtzite型结构的ZnO纳米环, 环内径约为220 nm, 壁厚约为70 nm. 反应物浓度、反应温度对ZnO纳米环的形成以及纳米环的尺寸都有一定的影响, 但起关键作用的是PAM-CTAC. 通过改变PAM-CTAC的浓度, 能有效地实现ZnO纳米环的可控合成. 室温荧光光谱显示, ZnO纳米环的紫外发射峰具有较窄的半高宽(FWHM)(约7 nm), 表明合成产物具有较窄的尺寸分布.     

Quantitative Bestimmung kleiner. Silbermengen mit Dithizon

Zusammenfassung 1. Es wird ein colorimetrisches Verfahren zur Bestimmung kleiner Ag-Mengen (zwischen etwa 120 und 10 Ag angegeben. Grundsätzlich wird es in der gleichen Weise ausgeführt wie die bereits veröffentlichte Methode zur Bestimmung kleiner Kupfermengen¹).2. Es wird ein Titrationsverfahren zur Bestimmung kleiner AgMengen (zwischen etwa 100 und 0,5 Ag) beschrieben. Im Prinzip besteht es in einer Titration der Ag-Lösung mit einer sehr verdünnten Lösung von Dithizon in CCl₄, welche gegen eine Ag-Lösung bekannten Gehaltes eingestellt wurde. Die Titration erfolgt im Scheidetrichter, mit dessen Hilfe die einzelnen Anteile der gebildeten Ag-Dithizonlösung abgetrennt werden. Der Endpunkt der Reaktion wird durch einen Farbumschlag von Gelb nach Grün angezeigt, der ohne Beeinträchtigung durch die gelbe Ag-Dithizonlösung gut erkennbar ist, da er nur in einem Bruchteil des Gesamtvolumens der gefärbten CCl₄-Lösung erzeugt wird.3. Das maßanalytische Verfahren ist wegen seiner vorzüglichen anreichernden Wirkung besonders zur quantitativen Spurensuche geeignet. In den meisten Elementen können bis zu 10^–3 oder 10^–4 % Ag bestimmt werden. Besonders eingehend untersucht wurde die Bestimmbarkeit von Ag neben Pb (bis zu 10^–5 % Ag), Zn, Cd, As, Sb und Bi.Im Cu sind weniger als 10^–2 % Ag bestimmbar.Bei geeigneter Modifikation der Methode läßt sich Ag z. B. auch neben der etwa 17fachen Menge Hg bestimmen. Die Bestimmung kleiner Ag-Gehalte im Au ist nach Durchführung der üblichen Au/Ag-Scheidung möglich.4. Kleine Ag-Mengen (zwischen 0,1 und 2 ) können auch neben anderen Metallen (außer Hg und den Edelmetallen) durch Mischfarben-colorimetrie angenähert bestimmt werden. Die Umsetzung geschieht z. B. mit einer violetten Lösung von Cu-Dithizon in CCl₄, wodurch Mischfarben zwischen Violett und Gelb erzeugt werden, welche mit Testlösungen bekannten Ag-Gehaltes verglichen werden.