Orientation change of adsorbed pyrazine on roughened rhodium electrodes as probed by surface-enhanced Raman spectroscopy

A surface-enhanced Raman spectroscopic (SERS) study of pyrazine adsorbed on roughened Rh electrodes was performed. Potential and concentration effects on the adsorption behavior of pyrazine were investigated. The SER spectra display four pairs of overlapping bands with the relative intensity of each pair being highly potential dependent, which has not been observed on other metals. The orientation change of the adsorbed pyrazine from the end-on to N/pi bonded edge-on configuration is proposed to account for this potential-dependent relative intensity change. This hypothesis is further supported by the SERS results obtained at different pyrazine concentrations. In conjunction with the orientation effect, the interaction of Rh with hydrogen and oxygen generated at different potentials has a great influence on the adsorption configuration of pyrazine.     

A surface-enhanced Raman study of the electrochemical reduction of 4-cyanopyridine

The adsorption and electroreduction of 4-cyanopyridine (4CP) on a silver electrode were studied by surface-enhanced Raman (SER) spectroscopy. The SER spectra indicate that the adsorbed 4CP takes end-on orientation on a silver electrode through the nitrogen atom in the pyridine ring. The softening and the cleavage of the C-C bond between the pyridine and the nitrile during the cathodic sweep were observed and discussed.     

SERS study of the interaction of thiourea with a copper electrode in sulphuric acid solution

The electrochemical interaction of thiourea with a copper electrode in sulphuric acid solution was investigated using Fourier transform Raman and in situ surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of thiourea at a copper electrode were obtained in solutions containing greater than 5 ppm thiourea; the spectra obtained were consistent with adsorption of the molecule on the copper electrode via the sulphur atom. The SERS spectra provide evidence of complex formation involving thiourea and sulphate species at the electrode surface.     

Surface-enhanced Raman spectroscopy of pentaammineosmium (III)/(II) and pentaammineruthenium (II) containing pyridine,pyrazine or 4,4′-bipyridine ligands at silver electrodes: vibrational assignments

Detailed vibrational assignments are described for surface-enhanced Raman (SER) spectra of pentaammineosmium (III), (II) and pentaammineruthenium (II) containing pyridine (py), pyrazine (pz) and 4,4′-bipyridine (bpy) ligands adsorbed at the silver—aqueous interface. The assignments are based on group symmetry analysis, deuteration effects and by comparison with corresponding normal Raman and i.r. spectra for the solid-phase complexes and surface and bulk Raman spectra for the corresponding free ligands. Most bands present in the normal Raman and/or i.r. spectra also appear in the SER spectra. This results from the high intensity of the SER spectra along with the relaxation of vibrational selection rules for adsorbed molecules. The appearance of intense SER spectra for Os (NH₃)₅py(III)/(II) and Ru^II(NH₃)₅py is noteworthy since, unlike free pyridine, these lack an available nitrogen for surface coordination. The results illustrate the virtues of electrochemical SER spectroscopy for examining the detailed vibrational properties of coordination compounds, including those in oxidation states [such as Os(II) here] that are difficult to obtain pure in bulk media.     

Preparation and characterization by surface-enhanced infrared absorption spectroscopy of silver nanoparticles formed on germanium substrates by electroless displacement

In this paper, the feasibility of applying electroless displacement to prepare silver nanoparticles (AgNPs) on the surface of germanium (Ge) substrate is demonstrated, and the performances of surfaces prepared in this manner for surface-enhanced infrared absorption (SEIRA) spectroscopy are reported. The process used to produce suitable AgNPs for SEIRA by electroless deposition is simple and effective, requiring only pretreatment of the germanium surface with hot air, immersion of the substrate in a dilute solution of silver nitrate, and washing of the resulting plate. To quantify the behavior of AgNPs on a Ge substrate and to optimize the conditions for the preparation of AgNPs on Ge substrates, a monolayer of p-nitrothiophenol (PNTP) was bonded to the surface of the AgNPs by immersion of the plate in a dilute solution of PNTP and measurement of the transmission spectrum. The factors that influenced the formation of AgNPs, and hence the SEIRA signals, included the concentration of AgNO₃, the reaction time and the temperature. Results indicated that stronger absorption bands in the SEIRA spectrum of a monolayer of PNTP were obtained if the reaction rate for the displacement of silver ions by Ge was slow. This condition was achieved by keeping the concentration of AgNO₃ and the reaction temperature low. Under the optimal conditions found in this work, an enhancement factor of approximately 100 was achieved for commonly used probe molecules in SEIRA measurements.     

In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

苯乙炔吸附在金电极上的现场表面增强拉曼光谱研究

采用电化学现场表面增强拉曼光谱研究了苯乙炔在金电极上的吸附行为及表面反应过程. 负电位下拉曼光谱的变化表明, 苯乙炔分子的炔端碳与金属电极成键, 分子垂直吸附于金电极表面. 在所研究的负电位区间内, 分子在电极表面的吸附取向并未随电位发生改变. 电化学现场光谱研究表明, 苯乙炔分子随电位负移, 碳碳叁键被加氢还原. 通过对比苯乙烯的现场表面增强拉曼光谱发现, 在－0.6 V至－1.2 V的电位区间内, 苯乙炔经过中间步骤生成苯乙烯, 最终被完全加氢为苯乙烷.     

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.     

Electroless deposition of gold thin films on silicon for surface-enhanced infrared spectroelectrochemistry

Electroless (or chemical) deposition technique has been used in preparing Au island film electrodes on Si for in situ infrared spectroscopic studies of the electrochemical interface in attenuated total reflection mode. Owing to surface-enhanced infrared absorption (SEIRA) effect, absorption bands of molecules adsorbed on the chemically deposited films were one order of magnitude as large as those observed on smooth Au electrode surfaces. Although the enhancement factor was identical to that observed on vacuum evaporated Au island films, this simple method is superior to vacuum evaporation method with respect to the adhesion of the film, surface contamination, reproducibility, and cost.     

Biochemical applications of surface-enhanced infrared absorption spectroscopy

An overview is presented on the application of surface-enhanced infrared absorption (SEIRA) spectroscopy to biochemical problems. Use of SEIRA results in high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders of magnitude and has the potential to enable new studies, from fundamental aspects to applied sciences. This report surveys studies of DNA and nucleic acid adsorption to gold surfaces, development of immunoassays, electron transfer between metal electrodes and proteins, and protein–protein interactions. Because signal enhancement in SEIRA uses surface properties of the nano-structured metal, the biomaterial must be tethered to the metal without hampering its functionality. Because many biochemical reactions proceed vectorially, their functionality depends on proper orientation of the biomaterial. Thus, surface-modification techniques are addressed that enable control of the proper orientation of proteins on the metal surface. Figure Surface enhanced infrared absorption spectroscopy (SEIRAS) on the studies of tethered protein monolayer (cytochrome c oxidase and cytochrome c) on gold substrate (left), and its potential induced surface enhanced infrared difference absorption (SEIDA) spectrum     

Concentration-dependent surface-enhanced Raman scattering of 2-benzoylpyridine adsorbed on colloidal silver particles

Surface-enhanced Raman scattering (SERS) of 2-benzoylpyridine (2-BP) adsorbed on silver hydrosols has been investigated. It has been observed that with a small change in the adsorbate concentration, the SER spectra of 2-BP show significant change in their features, indicating different orientational changes of the different part of the flexible molecule on the colloidal silver surface with adsorbate concentration. The time dependence of the SER spectra of the molecule has been explained in terms of aggregation of colloidal silver particles and co-adsorption and replacement kinetics of the adsorbed solute and solvent molecules on the silver surface. The broad long-wavelength band in the absorption spectra of the silver sol due to solute-induced coagulation of colloidal silver particles is found to be red-shifted with the increase in adsorbate concentration. The surface-enhanced Raman excitation profiles indicate that the resonance of the Raman excitation radiation with the new aggregation band contributes more to the SERS intensity than that with the original sol band.     

Surface-enhanced vibrational spectra of 2-nitrofluorene

The infrared and Raman spectra of the isolated adsorbate 2-nitrofluorene (2NF) have been registered and the spectral assignment was performed on the basis of both previous data concerning related molecules and density functional theory DFT calculations. The theoretical calculations were compared to the experimental results, obtaining a good agreement with the IR and Raman data. The surface-enhanced infrared and Raman spectra, SEIRA and SERS, of 2NF on different metal surfaces were registered; the best spectra were obtained by using the 633nm laser line. The most probable orientation and organization of the adsorbate on the surface were inferred from the reflection-absorption infrared spectrum RAIRS and SERS and SEIRA data.     

Interactions of ibuprofen with hybrid lipid bilayers probed by complementary surface-enhanced vibrational spectroscopies

The incorporation of small molecules into lipid bilayers is a process of biological importance and clinical relevance that can change the material properties of cell membranes and cause deleterious side effects for certain drugs. Here we report the direct observation, using surface-enhanced Raman and IR spectroscopies (SERS, SEIRA), of the insertion of ibuprofen molecules into hybrid lipid bilayers. The alkanethiol-phospholipid hybrid bilayers were formed onto gold nanoshells by self-assembly, where the underlying nanoshell substrates provided the necessary enhancements for SERS and SEIRA. The spectroscopic data reveal specific interactions between ibuprofen and phospholipid moieties and indicate that the overall hydrophobicity of ibuprofen plays an important role in its intercalation in these membrane mimics.     

Imaging the cell wall of living single yeast cells using surface-enhanced Raman spectroscopy

The surface of a living yeast cell (Saccharomyces cerevisiae strain W303-1A) has been labeled with silver (Ag) nanoparticles that can form nanoaggregates which have been shown to have surface-enhanced Raman scattering (SERS) activity. The cell wall of a single living yeast cell has been imaged by use of a Raman microspectroscope. The SERS spectra measured from different Ag nanoaggregates were found to be different. This can be explained on the basis of detailed spectral interpretation. The SERS spectral response originates from mannoproteins which cover the outermost regions of the yeast cell wall. Analysis of SERS spectra from the cell wall and the extracted mannoproteins from the yeast has been performed for the clarification of variation in SERS spectra.     

Fe(CN)_6~(3-/4-)在金电极上氧化还原过程的拉曼光谱研究

用电化学现场表面增强拉曼散射光谱研究了Fe（CN）63-/4-在金电极表面的氧化还原过程及吸附行为．结果表明，Fe（CN）63-/4-相对于Fe（CN）63-/4-能更强烈地吸附在金电极表面上，并通过配体CN-的N端吸附在电极表面．     

Detection of malathion in food peels by surface-enhanced Raman imaging spectroscopy and multivariate curve resolution

An analytical methodology was developed for detection of malathion in the peels of tomatoes and Damson plums by surface-enhanced Raman imaging spectroscopy and multivariate curve resolution. To recover the pure spectra and the distribution mapping of the analyzed surfaces, non-negative matrix factorization (NMF), multivariate curve calibration methods with alternating least squares (MCR-ALS) and MCR with weighted alternating least square (MCR-WALS) were utilized. Error covariance matrices were estimated to evaluate the structure of the error over all the data. For the tomato data, NMF-ALS and MCR-ALS presented excellent spectral recovery even in the absence of initial knowledge of the pesticide spectrum. For the Damson plum data, owing to heteroscedastic noise, MCR-WALS produced better results. This methodology enabled detection below to the maximum residue limit permitted for this pesticide. This approach can be implemented for in situ monitoring because it is fast and does not require extensive manipulation of samples, making its use feasible for other fruits and pesticides as well.     

纳米金三明治结构调制细胞色素c电子传递特性的分子机理研究

以细胞色素c(Cyt c)为模型蛋白,采用表面增强红外吸收光谱监测了三明治结构所吸附的纳米金对氧化还原诱导的Cyt c表面增强红外差谱的改变.研究表明,在单层Cyt c分子表面组装纳米金,使得血红素的红外差谱特征峰明显增强,这归因于纳米金和血红素之间的电子传递.纳米金与Cyt c氧化还原活性中心血红素的相互作用加速了蛋白质的电子传递.这为实现并优化表面吸附蛋白质的直接电化学提供了一种新技术.     

Surface-enhanced Raman scattering studies on the adsorption of p-nitrobenzoic acid at Au electrode under different potential with ultraviolet excitation

The potential-dependent surface-enhanced Raman spectrum of adsorbed p-nitrobenzoic acid (PNBA) on the roughened Au electrode has been obtained by using ultraviolet (UV) excitation at 325 nm. The surface-enhanced Raman spectra of PNBA intensely changed when the voltage was in the rang of negative value, and the electrode potential at which the resonance (potential of maximum intensity) occurs varied when the vibrational mode changes, indicating that the PNBA molecules were chemisorbed on the roughened Au surface. The charge transfer (CT) mechanism could probably explain the experiment results in the present work.     

过渡金属表面α-吡啶基的振动光谱学判据

基于簇模型采用密度泛函理论在B3LYP/6-311+G^**/LANL2DZ(metal)基组水平上计算了吡啶及α-吡啶基吸附于Pt、Pd、Rh、Ni四种金属表面的红外和拉曼光谱. 通过详细地分析和比较计算结果与文献报道的实验谱图, 提出了以N端吸附的吡啶分子和α-吡啶基这两种表面物种各自存在的谱学判据. 计算结果表明在以上四种金属表面, α-吡啶基的拉曼活性比吡啶的小, 而特征谱峰的红外强度与吡啶相当. 该结果表明红外光谱是检测金属表面α-吡啶基的有效手段, 也解释了采用表面增强拉曼光谱和红外光谱研究吡啶吸附在金属表面得出不同结构的原因.     

Influence of the solvent on the surface-enhanced raman spectra of ruthenium(II) bipyridyl complexes

In the present work a new dye, [Ru(dcbpyH2)2(bpy-TPA2)](PF6)2, and the well-known (Bu4N)2[Ru(dcbpyH)2(NCS)2] complex were investigated. The electronic transitions of both dyes showed solvatochromic shifts due to specific interactions of the ligands with the solvent molecules. The surface-enhanced Raman (SER) spectra of the dyes dissolved in water, ethanol, and acetonitrile were measured in silver and gold colloidal solutions. The results demonstrate that the dyes were adsorbed on the metallic nanoparticles in different ways for different solvents. It was also found that in the gold colloid, the aqueous solutions of both dyes did not produce any SERS signal, whereas in ethanolic solution the SERS effect was very weak. Deprotonation, H-bonding, and donor-acceptor interactions seem to determine these different behaviors. Our results indicate the important role of the charge-transfer mechanism in SERS.