Preparation of gold-tellurium hybrid nanomaterials for surface-enhanced Raman spectroscopy

We report a simple method for preparing three different SERS-active substrates. Concentrated hydrazine solution as the reducing agent and tellurium dioxide as the precursor were used to prepare Te nanowires (NWs). The as-prepared Te NWs have an average length of 547.7 +/- 111.6 nm and an average width of 15.1 +/- 2.7 nm. Through the reaction of Te NWs with sodium tetrachloroaurate in the presence of hexadecyltrimethylammonium bromide (CTAB) over reaction times of 10, 20, and 60 min, gold-tellurium nanodumbbells, gold-tellurium nanopeapods, and gold pearl-necklace nanomaterials (Au PNNs) were obtained, respectively. By controlling the reaction time, the distance between adjacent gold nanoparticles (Au NPs) in each Te nanowire was tunable, allowing us to investigate its effect on the SERS signals. Having shorter distances among Au NPs (greater electromagnetic fields), the Au PNNs provided a reproducible enhancement factor of 5.6 x 10(9).     

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.     

Stereoaligned Epitaxial Growth of Single‐Crystalline Platinum Nanowires by Chemical Vapor Transport

Epitaxial Pt nanowire (NW) arrays are synthesized for the first time by a chemical vapor transport method by using a metal halide as a precursor. Here we report that the epitaxial growth direction of NWs can be steered by seed crystal morphology. Octahedral seeds grow into inclined NWs possessing six growth directions, whereas half‐octahedral seeds grow into vertical and horizontal NWs. Interfacial energies between the seed material and the substrate are critical in determining the morphology of seed crystals. We also demonstrate that non‐SERS‐active Pt NWs can show strong surface‐enhanced Raman scattering (SERS) spectra by placing them on Ag films. The active SERS observation would help to elucidate platinum‐catalyzed chemical reactions.     

The ultratrace detection of crystal violet using surface enhanced Raman scattering on colloidal Ag nanoparticles prepared by electrolysis

Highly active,stable and affordable surface enhanced Raman scattering(SERS) substrates were obtained by electrolyzing a mixture of AgNO_3(4×10~(-4) mol/L) and Na_3C_6H_5O_7·H_2O(6×10~(-5) mol/L) for 1,2,3 and 4h at 7V.With crystal violet(CV) as a test molecule,a portable Raman spectrometer with 785 nm laser excitation was employed to carry out the SERS detection.Colloidal Ag nanoparticles prepared by electrolyzing for 3 h with the particle size of(65±17) nm is a perfect SERS substrate for the ultratrace ...     

Raman detection of localized transferrin-coated gold nanoparticles inside a single cell

We investigated the cellular uptake behavior of non-fluorescent metal nanoparticles (NPs) by use of surface-enhanced Raman scattering (SERS) combined with dark-field microscopy (DFM). The uptake of Au NPs inside a single cell could also be identified by DFM first and then confirmed by z-depth-dependent SERS at micrometer resolution. Guided by DFM for the location of Au NPs, an intracellular distribution assay was possible using Raman dyes with unique vibrational marker bands in order to identify the three-dimensional location inside the single cell by obtaining specific spectral features. Au NPs modified by 4-mercaptobenzoic acid (MBA) bearing its –COOH surface functional group were used to conjugate transferrin (Tf) protein using the 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) reaction. The protein conjugation reaction on Au surfaces was examined by means of color change, absorption spectroscopy, and SERS. Our results demonstrate that DFM techniques combined with SERS may have great potential for monitoring biological processes with protein conjugation at the single-cell level.     

Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass

A sandwich structure consisting of Ag nanoparticles (NPs), p-aminothiophenol (p-ATP) self-assembled monolayers (SAMs), and Ag NPs was fabricated on glass and characterized by surface enhanced Raman scattering (SERS). The SERS spectrum of a p-ATP SAM in such sandwich structure shows that the electromagnetic enhancement is greater than that on Ag NPs assembled on glass. The obtained enhancement factors (EF) on solely one sandwich structure were as large as 6.0 +/- 0.62 x 10(4) and 1.2 +/- 0.62 x 10(7) for the 7a and 3b(b(2)) vibration modes, respectively. The large enhancement effect of p-ATP SAMs is likely a result of plasmon coupling between the two layers of Ag NP (localized surface plasmon) resonance, creating a large localized electromagnetic field at their interface, where p-ATP resides. Moreover, the fact that large EF values (approximately 1.9 +/- 0.7 x 10(4) and 9.4 +/- 0.7 x 10(6) for the 7a- and b(2)-type vibration modes, respectively) were also obtained on a single sandwich structure of Au NPsp-ATP SAMsAg NPs in the visible demonstrates that the electromagnetic coupling does not exist only between Ag NPs but also between Au and Ag NPs. The lower EF values on Au-to-Ag NPs compared to those on Ag-to-Ag NPs demonstrate that the Au-to-Ag coupling must be less effective than the Ag-to-Ag coupling for the induction of SERS in the visible.     

Au Nanowire–Au Nanoparticles Conjugated System which Provides Micrometer Size Molecular Sensors

We report a new type of molecular sensor using a Au nanowire (NW)–Au nanoparticles (NPs) conjugated system. The Au NW–NPs structure is fabricated by the self‐assembly of biotinylated Au NPs on a biotinylated Au NW through avidin; this creates hot spots between NW and NPs that strongly enhance the Raman signal. The number of the Au NPs attached to the NW is reproducibly proportional to the concentration of the avidin, and is also proportional to the measured surface‐enhanced Raman scattering (SERS) signals. Since this well‐defined NW–NPs conjugated sensor is only a few micrometer long, we expect that development of multiplex nanobiosensor of a few tens micrometer size would become feasible by combining individually modified multiple Au NWs together on one substrate.     

Synthesis of ultrathin FePtPd nanowires and their use as catalysts for methanol oxidation reaction

We report a facile synthesis of ultrathin (2.5 nm) trimetallic FePtPd alloy nanowires (NWs) with tunable compositions and controlled length (<100 nm). The NWs were made by thermal decomposition of Fe(CO)(5) and sequential reduction of Pt(acac)(2) (acac = acetylacetonate) and Pd(acac)(2) at temperatures from 160 to 240 °C. These FePtPd NWs showed composition-dependent catalytic activity and stability for methanol oxidation reaction. Among FePtPd and FePt NWs as well as Pd, Pt, and PtPd nanoparticles (NPs) studied in 0.2 M methanol and 0.1 M HClO(4) solution, the Fe(28)Pt(38)Pd(34) NWs showed the highest activity, with their mass current density reaching 488.7 mA/mg Pt and peak potential for methanol oxidation decreasing to 0.614 V from 0.665 V (Pt NP catalyst). The NW catalysts were also more stable than the NP catalysts, with the Fe(28)Pt(38)Pd(34) NWs retaining the highest mass current density (98.1 mA/mg Pt) after a 2 h current-time test at 0.4 V. These trimetallic NWs are a promising new class of catalyst for methanol oxidation reaction and for direct methanol fuel cell applications.     

Colloidal systems of silver nanoparticles and high-regioregular cationic polythiophene with ionic-liquid-like pendant groups: Optical properties and SERS

We report tuning of structure dependent optical properties of colloidal systems of borate-stabilized silver nanoparticles (Ag NPs) and polythiophene-based cationic polyelectrolyte with ionic-liquid like side groups: poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) towards obtaining local electromagnetic field enhancement effects. Surface-enhanced Raman scattering (SERS) studies showed that the strong electromagnetic field enhancement is related to the formation of aggregates of Ag NPs achieved at the components ratio providing the charge balance between Ag NPs and cationic polythiophene, at which Ag NPs are nearly single-polymer-layer coated, their zeta potential is close to zero and they easily form aggregates in which the mean inter-particle distance enables the occurrence of desired plasmonic effects. Fluorescence quenching is efficient only in the systems with low concentrations of PMHT-Br, in which almost all polymer chains directly interact with the Ag NPs surface.     

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective enviromentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O₂.     

Self-assembly of silver nanoparticles: synthesis, stabilization, optical properties, and application in surface-enhanced Raman scattering

Silver nanoparticle aggregates were synthesized in large scale using resorcinol under alkaline condition to obtain an assembly of silver clusters. Stable dispersion of the cluster in aqueous medium has been examined out of resorcinol-capped silver nanoparticle assemblies. The UV-vis spectroscopy during the particle evolution has been studied in detail. From the high-resolution TEM (HRTEM) image and XRD pattern it was confirmed that the particles are made of pure silver only. The capping action of resorcinol has been authenticated from the FTIR spectra. UV-vis spectroscopy and TEM images reveal that the temperature, effect of vibrational energy, heat shock, and time-dependent particle evolution have unique bearing on the stability and surface properties of the clusters. The concentrations of silver nitrate, resorcinol, and NaOH have important influence on the particle evolution and its size. TEM images incite us to examine the aggregates to capitulate surface-enhanced Raman scattering (SERS) to the single molecular level using crystal violet (CV) and cresyl fast violet (CFV) as molecular probes. The SERS intensity of CV increases with increasing the size of the silver aggregate.     

Liposome-mediated enhancement of the sensitivity in immunoassay based on surface-enhanced Raman scattering at gold nanosphere array substrate

A novel immunoassay based on surface-enhanced Raman scattering (SERS) has been developed. The method exploits the SERS-derived signal from reporter molecules (crystal violet, CV) encapsulated in antibody-modified liposome particles. The antigen is firstly captured by the primary antibody immobilized in microwell plates and then sandwiched by secondary antibody-modified liposome. The CV molecules are released from the liposome and transferred to specially designed substrate of gold nanosphere arrays with sub-10-nm gaps. The concentration of the antigen is indirectly read out by the SERS intensity of the CVs. The substrate used could substantially improve the sensitivity and reproducibility of SERS measurement. The SERS intensity responses are linearly correlated to logarithm of antigen concentration in the range of 1.0 x 10(-8) to 1.0 x 10(-4) gm L(-1) with a detection limit of 8 ng mL(-1). To our knowledge, this is the first report describing liposome-mediated enhancement of the sensitivity in immunoassay based on surface-enhanced Raman scattering. Experimental results show that the proposed method illustrates a potential prospect of applications in immunoassay.     

用表面增强拉曼散射研究电解法制备的纳米银膜

用一种廉价的电解方法制备了纳米银膜,并详细研究了在这种银膜上的表面增强拉曼散射效果．结晶紫为本实验的检测性分子．通过实验发现,这种银膜用便携式拉曼光谱仪测试并计算出的表面增强拉曼散射的增强因子为603,并对结晶紫的最小检出限为0．1nmol／L．     

Ag/Si-NPA基底上共吸附R6G和CV的表面增强拉曼散射

以硅纳米孔柱阵列(Si-NPA)为基底, 采用浸渍沉积技术制备了具有较高表面增强拉曼散射(SERS)活性的Ag/Si-NPA衬底, 并采用扫描电子显微镜和透射电子显微镜对其表面形貌和结构进行了表征. 在此基础上, 选择罗丹明6G(R6G)和结晶紫(CV)2种生物染料分子并采用不同的混合吸附程序对其共吸附状态下的SERS光谱进行了探测. 结果表明, 当2种分子的溶液浓度均为10^-7 mol/L时, 无论采用何种浸渍吸附程序, 其SERS谱中CV的特征拉曼峰都被R6G完全掩盖. 对溶液采用错级配置(R6G和CV的浓度分别为10^-9和10^-7 mol/L)后, 所测SERS谱上获得了分别对应于R6G和CV的分离良好、相对强度匹配、分辨率高的2个SERS特征峰组, 从而有利于简化现实混合探测过程中对SERS特征峰的指认和判断.     

Synthesis method-dependent photothermal effects of colloidal solutions of platinum nanoparticles used in photothermal anticancer therapy

One of the most common anticancer therapies is photothermal therapy (PTT). The effectiveness of PTT depends on the photosensitizer being a molecule which is toxic for the cancer cells after electromagnetic wave irradiation. Therefore, a simulation of PTT was performed in this work on two colon cancer cells (SW480 and SW620) using platinum nanoparticles (Pt NPs). Interestingly, in the literature the dependence between the synthesis method and the photothermal properties of Pt NPs was not discussed. Consequently, in this paper, we evaluated the photothermal properties of Pt NPs synthesized by two different methods: polyol (PtI NPs) and green chemistry (PtII NPs). Scanning transmission electron microscopy revealed that the size of both Pt NPs obtained was 2 nm, the NPs were not agglomerated, and that the PtII NPs were distributed on green tea supports. The selected area electron diffraction and X-ray diffraction analysis confirmed the crystallinity of both types of Pt NPs. Fourier-transform infrared (FTIR) spectrum of the PtII NPs showed interactions between the NPs and stretching modes for C=O groups from flavonoids and polyphenols. Therefore, these chemical compounds could be responsible for reducing Pt⁴⁺ ions to Pt⁰. Moreover, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay showed that the PtII NPs exhibited 10% and 20% better cytotoxicity effect on SW480 and SW620 cells, than PtI NPs. The viability of cancer cells decreased when Pt NPs were used in PTT. The highest percentage of dead cells (82%) was observed for PtII NPs and 650-nm laser irradiation. FTIR and Raman spectroscopy showed structural changes induced by both Pt NPs and laser irradiation of cells in the range corresponding to levels of DNA, phospholipids, proteins, and lipids. Moreover, the calculated photothermal conversion efficiency showed that the value of this parameter is around 35%, regardless of the synthesis method and used wavelengths.     

预制铂纳米颗粒对质子交换膜燃料电池用铂纳米线阴极的结构影响

铂纳米线（Pt NWs）由于其独特的结构特点,比商业Pt/C具有更高的氧还原反应（ORR）比活性。在本工作中,我们将预先制备好的铂纳米颗粒（Pt NPs）引入到碳基体中,用于诱导生长Pt NWs,获得了均匀分布Pt NWs的阴极。通过改变Pt NP载量（0~0.015 mg·cm^-2）和Pt NP来源（不同Pt含量的Pt/C）研究了所制备阴极的结构和性能。用扫描电镜对阴极表面进行了表征,并用透射电镜和X射线衍射分析了Pt NW的形貌和晶体结构。在单电池中分别进行了极化曲线和循环伏安曲线测试。当Pt NP来源为40% Pt/C且其载量为0.005 mg·cm^-2时,制备的Pt NW阴极具有最佳的单电池性能和最大的电化学表面积（ECSA）。最后,提出了预制Pt NP影响Pt NWs分布的可能机制。     

Facile preparation of Pt hydrosols by dispersing bulk Pt with potential perturbations

Pt hydrosols have been synthesized by dispersing a pure Pt wire in a NaOH solution with square wave potential (SWP) or alternating voltage (AV). The rearrangements of superfacial Pt atoms by repeated and fast electro-redox under the potential perturbations (PPs), coupling with the impetus of concurrent hydrogen gas, account for this novel dispersion of bulk Pt. Using this strategy we are able to realize the green and facile synthesis of clean Pt nanoparticles (NPs) requiring no any precursor ions and reducers in aqueous solution under mild conditions. Moreover, the dispersion of bulk Pt has also been carried out by paired electrolysis with two Pt wires. The as-prepared Pt NPs were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The Pt NPs exhibit high electrocatalytic activity toward the ethanol electrooxidation and weak surface-enhanced Raman scattering (SERS) signals for adsorbed pyridine.     

Differential SERS activity of gold and silver nanostructures enabled by adsorbed poly(vinylpyrrolidone)

We report that poly(vinylpyrrolidone) (PVP), a common stabilizer of colloidal dispersions of noble metal nanostructures, has a dramatic effect on their surface-enhanced Raman scattering (SERS) activity and enables highly selective SERS detection of analytes of various type and charge. Nanostructures studied include PVP-stabilized Au-Ag nanoshells synthesized by galvanic exchange reaction of citrate-reduced Ag nanoparticles (NPs), as well as solid citrate-reduced Ag and Au NPs, both before and after stabilization with PVP. All nanostructures were characterized in terms of their size, surface plasmon resonance wavelength, surface charge, and chemical composition. While the SERS activities of the parent citrate-reduced Ag and Au NPs are similar for rhodamine 6G (R6G) and 1,2-bis(4-pyridyl)ethylene (BPE) at various pH values, PVP-stabilized nanostructures demonstrate large differences in SERS enhancement factors (EFs) between these analytes depending on their chemical nature and protonation state. At pH values higher than BPE's pK(a2) of 5.65, where the analyte is largely unprotonated, the PVP-coated Au-Ag nanoshells showed a high SERS EF of >10(8). In contrast, SERS EFs were 10(3)- to 10(5)-fold lower for the protonated form of BPE at lower pH values, or for the usually highly SERS-active cationic R6G. The differential SERS activity of PVP-stabilized nanostructures is a result of discriminatory binding of analytes within-adsorbed PVP monolayer and a subsequent increase of analyte concentration at the nanostructure surface. Our experimental and theoretical quantum chemical calculations show that BPE binding with PVP-stabilized Au-Ag nanoshells is stronger when the analyte is in its unprotonated form as compared to its cationic, protonated form at a lower pH.     

Effect of silver nanowires on the surface-enhanced Raman spectra (SERS) of the RNA bases

RNA bases have a great importance in the biological and genetics applications. The surface-enhanced Raman scattering (SERS) was used to study the orientation and adsorption structure of RNA bases adsorbed on the surface of silver nanowires (Ag NWs). The Ag NWs were prepared and its UV-vis spectra were recorded. The RNA bases oriented perpendicularly on the surface of Ag NWs, as the coverage area decreases. Consequently, the in-plane bands were enhanced according to the SERS selection rule. Many bands were red shifted due to the chemisorption of RNA bases on the Ag NWs surface. New bands corresponding to the base-surface bond were appeared in the SERS spectra.     

粗糙铂电极上甲酸吸附氧化的电化学原位表面增强拉曼光谱研究

采用循环伏安法和电化学原位表面增强拉曼光谱（SERS）技术研究甲酸的解离 及附与氧化行为。首次报道了甲酸吸附、解离和氧化的电化学原位SERS谱，发现甲 酸在粗糙铂电极上能自发解离吸附；首欠成功地获得了粗糙铂电极上甲酸吸附解离 的强吸附中间体CO和活性中间体COOH的表面增强拉曼光谱，同时首次检测到甲酸氧 化最终产物CO_2的拉曼光谱信号，从分子水平证实甲酸解离吸附反应的双途径机理 。