Surface enhanced Raman spectroscopic studies on 1H-1,2,4-triazole adsorbed on silver colloidal nanoparticles

1H-1,2,4-triazole is a very effective corrosion inhibitor for copper. The adsorption of this compound on silver colloidal nanoparticles has been studied by means of surface enhanced Raman scattering (SERS). SERS data are interpreted with the help of DFT calculations of models of the surface complex formed by 1H-1,2,4-triazole on the silver colloidal nanoparticles surface. It was found that this compound is adsorbed on metal surface in its anionic form and that it interacts with silver through the N₁ and N₂ atoms. The molecular plane assumes a tilted orientation with respect to the silver surface.     

Stable and efficient silver substrates for SERS spectroscopy

Silver substrates have been obtained, by depositing silver colloidal nanoparticles on a roughened silver plate treated with 1,10-phenanthroline, and checked by means of AFM microscopy and Raman spectroscopy. The ligand molecules are located between two silver substrates and undergo the SERS (Surface Enhanced Raman Scattering) enhancement of both the roughened silver plate and the silver colloidal layer deposited on it. These SERS-active substrates, which show the advantages of being stable with respect to the metal colloidal suspensions, along with an easy and reproducible preparation, can be very useful for catalytic and analytical applications of the SERS spectroscopy.     

SERS Investigation on the Polymerization of Carbazolyl-diacetylene Monolayers on Gold Surfaces

Surface Enhanced Raman Scattering experiments were performed on self-assembled carbazolyl-diacetylene monolayers chemisorbed on smooth gold substrates and UV irradiated. The Raman enhancement was ensured by depositing silver colloidal nanoparticles, which strongly increase the surface roughness. The co-existence of two polymer phases, characterized by different degree of order in the polymeric backbone, was detected by SERS results, which suggest a polymerization scheme with conjugated triple bonds nearly parallel to the plane of the metal surface.     

Vibrational study of the salicylate interaction with metallic ions and surfaces

Infrared and Raman spectroscopy are used in this work to study the metallic complexes of salicylic acid with silver and copper, comparing the interaction between salicylate and the cations (Ag+ and Cu2+) in the metal complexes with the SERS spectra when adsorbed on colloidal metal surfaces of the same metals. The salicylate complexes with the above metals were compared to those of Na+, Fe3+ and Al3+ cations. A different interaction mechanism is deduced for salicylate in the metal complex and when adsorbed on the metal surface.     

Adsorption mechanisms of sulfathiazole on gold,silver and copper surfaces studied by SERS

Surface-enhanced Raman scattering (SERS) of sulfathiazole was studied in gold, silver and copper colloids as well as on a gold plate. SERS spectra of sulfathiazole in gold and silver colloids indicated chemisorption of molecules on the metal nanoparticles through the amide nitrogen, with the phenyl moiety orthogonally placed and the thiazole ring almost parallel positioned towards the metal surface. Although selectively enhanced phenyl bands pointed to a very similar position of the sulfathiazole molecules on the copper colloid, a chemical bonding was not implied. Unlike adsorption mechanisms and position of the molecules on the colloid metal surfaces, a sideway adsorption of sulfathiazole on the gold plate was proposed. Hereby, both, the amide nitrogen and the thiazole nitrogen were considered responsible for approaching of sulfathiazole to the gold enhancing surface.     

Vibrational and surface-enhanced vibrational spectra of 6-nitrochrysene

The infrared and Raman spectra of solids and thin solid films of 6-nitrochrysene, its electronic spectra, and resonance Raman scattering (RRS) obtained with UV-laser excitation at 325 nm are reported. The vibrational assignment is supported by ab initio computations at the B3LYP/6-311G(d, p) level of theory. The molecular organization in nanometric films evaporated onto smooth metal surfaces of silver and copper was probed using reflection-absorption infrared spectroscopy (RAIRS). The results of the surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) obtained from nanometric films evaporated onto silver island films are also discussed. It was found that the molecule efficiently interacts with silver island film surfaces, and that the interaction leads to extensive photochemical reaction at the metal surface under laser illumination.     

Assembly of Multilayered Films on Core Substrate:Preparation and Characterization

Certain colloidal metals such as.silver (Ag), gold (Au) and copper, (Cu), when properly or assembled, display remarkable enhancement effect to the Raman scattering cross section of adsorbed molecules. This surface-enhanced Raman scattering (SERS) phenomenon has found wide applications in the study of interfacial chemical processes and is a potentially non-invasive technique in molecule-specific analysis. However, the SERS activity of metal colloids depends sensitively on both the synthetic method and the aggregation and assembly procedure, making it difficult to develop SERS into a reliable and quantitative analytical technique. To solve this problem, one needs to develop a substrate with a well-defined adsorption area and SERS activity. One approach to achieve this goal is to assemble a monolayer of uniform colloidal metals onto a well-defined secondary substrate. Here we report our effort in assembling monolayers of uniform Au nanoparticles on the well-defined optical-inactive microparticles in a layer-by-layer (LbL) manner and the use of such assembly as SERS-active substrate.     

Towards single-microorganism detection using surface-enhanced Raman spectroscopy

The identification and discrimination of microorganisms is important not only for clinical reasons but also for pharmaceutical clean room production and food-processing technology. Vibrational spectroscopy such as IR, Raman, and surface-enhanced Raman scattering (SERS) can provide a rapid ‘fingerprint’ on the chemical structure of molecules and is used to obtain a ‘fingerprint’ from microorganisms as well. Because of the requirement that a single bacterium cell and noble metal nanoparticles must be in close contact and the lack of a significant physical support to hold nanoparticles around the single bacterium cell, the acquisition of SERS spectra for a single bacterium using colloidal nanoparticles could be a challenging task. The feasibility of SERS for identification down to a single bacterium is investigated. A Gram-negative bacterium, Escherichia coli, is chosen as a model for the investigation. Because the adsorption of silver nanoparticles onto the bacterial cell is an exclusive way for locating nanoparticles close to the bacterium cell, the absorption characteristics of silver nanoparticles with different surface charges are investigated. It is demonstrated that the citrate-reduced colloidal silver solution generates more reproducible SERS spectra. It is found that E. coli cells aggregate upon mixing with silver colloidal solution, and this may provide an additional benefit in locating the bacterial cell under a light microscope. It is also found that a laser wavelength in the UV region could be a better choice for the study due to the shallow penetration depth. It is finally shown that it is possible to obtain SERS spectra from a single cell down to a few bacterial cells, depending on the aggregation properties of bacterial cells for identification and discrimination.     

C70分子吸附于铜表面的增强拉曼光谱研究

报道了C70分子吸附于铜表面的增强拉曼光谱.通过与正常拉曼光谱以及银表面SERS谱的比较发现,C70分子与铜表面之间的吸附属于物理吸附,增强机制主要是电磁增强.C70分子在银表面上的吸附状态与铜表面上的不同,这导致了两者特征峰谱线强度分布存在差异.以C60的振动模式为参考,推断出C70分子在2种金属表面上的吸附状态可能分别处于使碳笼的挤压振动模接近于“平躺”和“竖直”的2种状态.     

金核银壳纳米粒子薄膜的制备及SERS活性研究

采用柠檬酸化学还原法制备金溶胶, 通过自组装技术在石英片表面制备金纳米粒子薄膜, 在银增强剂混合溶液中反应获得金核银壳纳米粒子薄膜. 用紫外-可见吸收光谱仪和原子力显微镜(AFM)研究了不同条件下制备的金核银壳纳米粒子薄膜的光谱特性和表面形貌, 并以结晶紫为探针分子测量了金核银壳纳米粒子薄膜的表面增强拉曼光谱(SERS). 结果表明, 金纳米粒子薄膜的分布、银增强剂反应时间的长短对金核银壳纳米粒子薄膜的形成均有重要影响. 制备过程中, 可以通过控制反应条件获得一定粒径的、具有良好表面增强拉曼散射活性的金核银壳纳米粒子薄膜.     

气液界面磷脂单分子膜的表面增强拉曼光谱

采用纳米银胶作为成膜亚相, 原位获得了十八胺单分子膜、十八胺/卵磷脂复合膜的表面增强拉曼信号.研究表明,增强主要来源于亚相中的银粒子与成膜分子之间较强的作用.通过在磷脂膜内添加十八胺分子辅助增强而获取了卵磷脂的分子振动信息.     

Surface-enhanced Raman scattering measurements on silver nanoparticles covered with differently formed platinum films

Gold and silver electromagnetic nanoresonators covered by a thin layer of platinum are often used to study adsorption of various molecules on “model platinum surfaces” with surface-enhanced Raman scattering (SERS) spectroscopy. In this contribution spectra of pyridine adsorbed on films formed from core–shell Ag@Pt and Ag@Ag–Pt nanoparticles and pure Pt or Ag nanoparticles were measured using a confocal Raman microscope. The SERS spectra of pyridine adsorbed on alloy Ag@Ag–Pt nanoparticles could not be obtained as a linear combination of spectra measured on pure Ag and Pt surfaces. In other words, for silver electromagnetic nanoresonators covered by platinum there is no simple correlation between the “quality” of the deposited Pt layer and the relative intensity of SERS bands characteristic for adsorbate interacting with silver. The SERS spectra accumulated from various places of a film formed from Ag@Pt or Ag@Ag–Pt nanoclusters may differ significantly. Using Ag@Pt nanoparticles with practically negligible amount of Ag on the surface (as per the stripping measurement), it is possible to record SERS spectrum in which the contribution characteristic for pyridine adsorbed on the Ag surface is well visible. It means that, even for macroscopic samples of core–shell Ag–Pt nanoparticles, averaging of many spectra measured at various locations of the sample should be carried out to characterize reliably their properties.     

Adsorption Behaviors of 4-Mercaptobenzoic Acid on Silver and Gold Films

The adsorption behaviors of 4-mercaptobenzoic acid on silver and gold nanoparticles were studied by surface-enhanced Raman scattering (SERS) and density functional theory. The silver and gold films by electrodeposition have the same excellent characteristics as SERS-active substrates. At the same, the SERS spectra indicate that 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of gold nanoparticles through the S atom, and that the carboxyl group is far away from surface of gold nanoparticles, and that there is a certain angle between the plane of benzene ring and gold film. However, 4-mercaptobenzoic acid molecules are adsorbed on the surfaces of silver nanoparticles through the carboxyl group, and the S atom is far away from surface of silver nanoparticles, and there is also a certain angle between the plane of benzene ring and the surface of silver nanoparticles. Here it is demonstrated the calculated Raman frequencies are in good agreement with experimental values, and the calculated Raman frequencies are also helpful to infer the adsorption behaviors of 4-mercaptobenzoic acid molecules.     

Silver–platinum core–shell nanoparticles for surface-enhanced Raman spectroscopy

Core–shell Ag@Pt nanoparticles have been synthesised by the means of seed-growth reaction including reduction of PtCl₄²⁻ with silver and replacing Ag atoms with Pt. Surface-enhanced Raman scattering (SERS) spectra of pyridine (which gives slightly different spectra when interacting with various metals) adsorbed on synthesised Ag@Pt clusters were measured. SERS measurements have revealed that deposition of the platinum layer causes near elimination of the spectral interferences from pyridine directly interacting with the silver core. The average SERS enhancement factor for pyridine adsorbed on the Ag@Pt clusters was estimated as equal to about 10³–10⁴, significantly higher than the SERS enhancement factor achievable on the pure platinum nanostructures. Using the silver core (instead of the previously used gold cores) allows for measurement of strong SERS spectra on the Pt covered nanostructures for the wider range of the excitation radiation. This procedure of platinum deposition was tested with various silver nanoparticles – produced with borohydride, citrate and citrate/borohydride methods – which substantially differ in size distribution. The application of formed Ag@Pt structures for obtaining intense Raman spectra for molecules adsorbed on only slightly modified platinum surfaces is discussed.     

Enhanced and normal Raman scattering from pyridine adsorbed on rough and smooth silver electrodes

A multiplex spectrograph has been used to record potential difference and modulation Raman spectra of pyridine adsorbed on silver electrodes in an electrochemical cell. Spectra have been obtained from rough silver surfaces which give SERS and from surfaces where SERS has been diminished by prolonged cathodic polarisation (DSERS). Raman scattering from pyridine at smooth silver surfaces in potassium perchlorate and fluoride solutions has been distinguished from solution scatter by a potential modulation technique. The results show that the enhanced scattering caused by silver atom or cluster sites is respresentative of the surface as a whole as similar Raman spectra are obtained on smooth surfaces at a count rate as low as ?1.4 photons s^?1 (incident laser power 500 mW).Correlation of simultaneous differential capacitance data and “snapshot” SER spectra indicate that pyridine molecules in aqueous chloride ion solutions adsorb on silver in a flat π-bonded configuration at potentials markedly positive to the point of zero charge and exhibit specific reorientation at ?0.3 V and ?0.45 V (vs. SCE) to become N-bonded, perpendicular to the surface. Results also show that the adsorption behaviour of pyridine in chloride and fluoride ion solutions is largely similar.     

Silver Nanoparticle Thin Films with Nanocavities for Surface‐Enhanced Raman Scattering

The formation of nanometer‐sized gaps between silver nanoparticles is critically important for optimal enhancement in surface‐enhanced Raman scattering (SERS). A simple approach is developed to generate nanometer‐sized cavities in a silver nanoparticle thin film for use as a SERS substrate with extremely high enhancement. In this method, a submicroliter volume of concentrated silver colloidal suspension stabilized with cetyltrimethylammonium bromide (CTAB) is spotted on hydrophobic glass surfaces prepared by the exposure of the glass to dichloromethysilane vapors. The use of a hydrophobic surface helps the formation of a more uniform silver nanoparticle thin film, and CTAB acts as a molecular spacer to keep the silver nanoparticles at a distance. A series of CTAB concentrations is investigated to optimize the interparticle distance and aggregation status. The silver nanoparticle thin films prepared on regular and hydrophobic surfaces are compared. Rhodamine 6G is used as a probe to characterize the thin films as SERS substrates. SERS enhancement without the contribution of the resonance of the thin film prepared on the hydrophobic surface is calculated as 2×10⁷ for rhodamine 6G, which is about one order of magnitude greater than that of the silver nanoparticle aggregates prepared with CTAB on regular glass surfaces and two orders of magnitude greater than that of the silver nanoparticle aggregates prepared without CTAB on regular glass surfaces. A hydrophobic surface and the presence of CTAB have an increased effect on the charge‐transfer component of the SERS enhancement mechanism. The limit of detection for rhodamine 6G is estimated as 1.0×10^?8 M . Scanning electron microscopy and atomic force microscopy are used for the characterization of the prepared substrate.     

Surface-enhanced Raman scattering sensor for theophylline determination by molecular imprinting on silver nanoparticles

A surface-enhanced Raman scattering (SERS)-based sensor for the determination of theophylline (THO) has been developed by imprinting the target molecules on the surface of silver nanoparticles. The desired recognition sites are generated after template removal and homogeneous distribution on the silver nanoparticles that have been incorporated within polymer matrix by the in situ reduction of theophylline-silver complexes, providing molecular recognition ability and SERS active surfaces. The theophylline molecules, complementary to the shape, size, and functionality of the recognition cavities, can selectively bind to the recognition sites at the surface of silver nanoparticles driven by the formation of hydrogen bonding and surface coordination. It has been demonstrated that the SERS signals of the theophylline molecules captured on the surface of the silver nanoparticles have a good reproducibility and a dose-response relationship to the target analytes, showing the potential for reliable identification and quantification of the bioactive compound. The molecular imprinting-based SERS sensor, like antibodies or enzymes, also possesses the ability to distinguish theophylline from the closely related structure caffeine due to the variations of molecular size and shape as well as the different affinity to silver ions.     

Silver Coated Platinum Core–Shell Nanostructures on Etched Si Nanowires: Atomic Layer Deposition (ALD) Processing and Application in SERS

A new method to prepare plasmonically active noble metal nanostructures on large surface area silicon nanowires (SiNWs) mediated by atomic layer deposition (ALD) technology has successfully been demonstrated for applications of surface‐enhanced Raman spectroscopy (SERS)‐based sensing. As host material for the plasmonically active nanostructures we use dense single‐crystalline SiNWs with diameters of less than 100 nm as obtained by a wet chemical etching method based on silver nitrate and hydrofluoric acid solutions. The SERS active metal nanoparticles/islands are made from silver (Ag) shells as deposited by autometallography on the core nanoislands made from platinum (Pt) that can easily be deposited by ALD in the form of nanoislands covering the SiNW surfaces in a controlled way. The density of the plasmonically inactive Pt islands as well as the thickness of noble metal Ag shell are two key factors determining the magnitude of the SERS signal enhancement and sensitivity of detection. The optimized Ag coated Pt islands on SiNWs exhibit great potential for ultrasensitive molecular sensing in terms of high SERS signal enhancement ability, good stability and reproducibility. The plasmonic activity of the core‐shell Pt//Ag system that will be experimentally realized in this paper as an example was demonstrated in numerical finite element simulations as well as experimentally in Raman measurements of SERS activity of a highly diluted model dye molecule. The morphology and structure of the core‐shell Pt//Ag nanoparticles on SiNW surfaces were investigated by scanning‐ and transmission electron microscopy. Optimized core–shell nanoparticle geometries for maximum Raman signal enhancement is discussed essentially based on the finite element modeling.     

Comparative study of the morphology, aggregation, adherence to glass, and surface-enhanced Raman scattering activity of silver nanoparticles prepared by chemical reduction of Ag+ using citrate and hydroxylamine

Two different silver colloids were prepared by chemical reduction of silver nitrate with trisodium citrate and hydroxylamine hydrochloride to compare their characteristics in relation to their possible use in surface-enhanced Raman scattering (SERS) spectroscopy. The morphology and plasmon resonance of the single nanoparticles and aggregates integrating these colloids were characterized by means of UV-vis absortion spectroscopy and scanning electron microscopy, revealing important differences between each type of nanoparticle as concerns their physical properties. These metallic systems also manifested differences in the aggregation and the adherence to glass surfaces, revealing significant differences in the chemical surface properties of these nanoparticles. SERS and surface-enhanced IR also indicated the presence of interference bands which can overlap the spectra of the analyte, mainly in the case of the citrate colloid. All these differences have an important influence on the applicability of these nanostructured systems in SERS. In fact, the enhancement factor and spectral pattern of the SERS obtained by using alizarin as a molecule probe are different.     

预聚集法制备单层银纳米粒子膜及其SERS活性研究

提出一种预聚集方法来制备单层银纳米粒子膜, 获得了高活性的表面增强拉曼散射基底. 利用紫外-可见吸收光谱、TEM, SEM等表征手段分析了预聚集程度对银纳米单层膜基底SERS活性的影响. 实验发现该方法制备的银纳米粒子膜的SERS活性与预聚集程度直接相关, 在最优参数下制备的SERS基底具有银颗粒分布均匀、SERS活性均一、增强效果好等优点. 实验分别以罗丹明6G (R6G)、3-巯基丙酸(3MPA)和9-氨基吖啶盐酸盐(9AA)为探针对所制备基底的SERS活性进行了测试, 结果均获得了高信噪比的SERS信号.