Surface‐enhanced Raman scattering of hydroxyproline

Surface‐enhanced Raman scattering (SERS) spectra of hydroxyproline and one deuterated analogue are reported. In this work, we tackled the problem of SERS reproducibility by employing gold colloids instead of the usual silver sols to achieve plasmon enhanced Raman scattering. We slightly modified modified a previously published procedure to obtain to obtain the colloid, and concentrated the gold particles by centrifugation. The SERS spectra show distinctive bands of hydroxyproline, assigned by comparison to normal Raman spectra and density functional theory calculations. Repeated measurements using this procedure showed reproducible SERS spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of calixarene to high active surface‐enhanced Raman scattering (SERS) substrates suitable for in situ detection of polycyclic aromatic hydrocarbons (PAHs) in seawater

The characteristics of the sol–gel matrix embedding Ag nanoparticles functionalized with 25,27‐dimercaptoacetic acid‐26,28‐dihydroxy‐4‐tert‐butylcalix[4]arene (DMCX) suitable for the in situ detection of polycyclic aromatic hydrocarbons (PAHs) in seawater is presented. The DMCX‐functionalized silver nanoparticles were produced by the thermal reduction method in xerogel film. The silver colloid blocks were formed in the sol–gel matrix, with a diameter ranging from 50 to 120 nm. DMCX forming the monolayer on the silver nanoparticle surface contributes to the surface‐enhanced Raman scattering (SERS) activity due to the aggregation of silver nanoparticles and the preconcentration of PAH molecules within the zone of electromagnetic enhancement. When selected, PAH molecules e.g. pyrene and naphthalene were adsorbed onto the SERS substrate; Raman band positions of PAH were slightly shifted. A calibration procedure reveals that this type of SERS substrate has a limit of detection of 3 × 10⁻¹⁰ mol/l for pyrene and 13 × 10⁻⁹ mol/l for naphthalene in artificial seawater. The Raman signal response on a pyrene concentration change in artificial seawater was evaluated using a 671‐nm Raman setup with a flow‐through cell. This type of SERS substrate will be suitable for the in situ trace detection of pollutant chemicals in seawater. Copyright © 2012 John Wiley & Sons, Ltd.     

Trace analysis of polycyclic aromatic hydrocarbons using calixarene layered gold colloid film as substrates for surface‐enhanced Raman scattering

A surface‐enhanced Raman scattering (SERS) active substrate for the detection of polycyclic aromatic hydrocarbons (PAHs) was developed, which used 25, 27‐dimercaptoacetic acid‐26, 28‐dihydroxy‐4‐terbutyl calix[4]arene (DMCX) to functionalize a gold colloid film. This SERS‐active substrate prepared by self‐assembly method exhibits a high sensitivity, especially for the detection of PAHs. With the use of this SERS‐active substrate and with the application of the shifted excitation Raman difference spectroscopy (SERDS) technique, Raman signals of pyrene and anthracene in aqueous solutions at low concentration level (500 pM) can be obtained. Moreover, because PAHs are blocked from being directly adsorbed on gold colloid by DMCX and the photochemical reactions of adsorbates are avoided, the Raman bands of PAHs adsorbed on DMCX‐fuctionalized gold colloid film can be one‐to‐one correspondence with those of solid PAHs, and additionally, this SERS‐active substrate can be easily cleaned and reused. The obtained results demonstrate that the DMCX‐functionalized gold colloid films prepared by self‐assembly method have great potential to be developed to an in situ PAHs detection substrate. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman,infrared, SERS and theoretical study of 3‐(1‐phenylpropan‐2‐ylamino) propanenitrile,fenproporex

Infrared, Raman and surface‐enhanced Raman scattering (SERS) spectra of 3‐(1‐phenylpropan‐2‐ylamino)propanenitrile (fenproporex) have been recorded. Density functional theory (DFT) with the B3LYP functional was used for optimizations of ground state geometries and simulation of Raman and SERS vibrational spectra of this molecule. Bands of the vibrational spectra were assigned in detail. The comparison of SERS spectra obtained by using colloidal silver and gold nanoparticles with the corresponding Raman spectrum reveals enhancement and shifts in bands, suggesting a possible partial charge‐transfer mechanism in the SERS effect. Information about the orientation of fenproporex on the nanometer‐sized metal structures is also obtained. Copyright © 2011 John Wiley & Sons, Ltd.     

An improved self‐assembly gold colloid film as surface‐enhanced Raman substrate for detection of trace‐level polycyclic aromatic hydrocarbons in aqueous solution

To detect trace‐level polycyclic aromatic hydrocarbons, some investigations of an improved self‐assembly method are carried out using gold colloid films for the preparation of the surface‐enhanced Raman scattering (SERS)‐active substrate. Extinction spectra and scanning electron microscopy images reveal that controllable surface plasmonic metal substrates can be obtained by increasing the temperature of (3‐aminopropyl)trimethoxysilane solution up to 64.5 °C. The SERS‐active substrates have a high enhancement factor, and they can be both easily prepared and reproducible. With the use of these substrates, different concentrations of pyrene and anthracene in aqueous solutions were detected by SERS. A further enhancement can be supported by shifted excitation Raman difference spectroscopy. Raman signals of pyrene and anthracene adsorbed on gold colloid substrates up to limits of detection at 5 and 1 nmol/l, respectively, can be obtained. The quantitative analysis shows the possibility of in situ detection of polycyclic aromatic hydrocarbons while such gold colloid film serves as a SERS‐active substrate. Copyright © 2012 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and computational study of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate

FT‐IR and FT‐Raman spectra of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate (MDIE) were recorded and analyzed. Surface‐enhanced Raman scattering (SERS) spectra were recorded in silver colloid and silver electrode. The vibrational wavenumbers were computed using HF/6‐31G* and B3LYP/6‐31G* basis. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in infrared and Raman spectroscopies as well as in SERS of the studied molecule. The first hyperpolarizability and infrared intensities are reported. The geometrical parameters of the title compound are in agreement with the reported similar derivatives. The presence of new bands at 1045 and 948 cm⁻¹ in the SERS spectrum in silver electrode is related to the change in orientation of the molecule with respect to the metal surface. In silver colloid SERS spectrum, the methyl group attached to the methoxy carbonyl group is close to the metal surface, whereas on silver electrode the methyl group attached to the phenyl ring is close to the metal surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of Surface‐Enhanced Raman Scattering for ex Situ and in Situ Investigations of Polythiophene Derivatives

Polythiophene derivative films have been synthesized on electrochemically roughened silver, gold, and copper electrodes by anodic oxidation of the corresponding monomers. Surface‐enhanced Raman scattering (SERS) analyses of these coatings led to high‐quality spectra with high signal‐to‐noise ratios. In contrast with platinum, the use of SERS‐active metals allowed the observation of important changes in the positions, widths, and relative intensities of the Raman bands during the polymer doping‐dedoping process. In situ SERS investigations revealed that the modifications in the spectral features, when the polymer oxidation degree is progressively increased, are due to a transition from the aromatic to the quinoid structure and to an increase of structural defects along the polymer chains. Moreover, in the case of soluble polyalkylthiophene films, SERS analyses were also carried out using colloidal silver solutions. Despite the very low polymer concentration and the mild experimental conditions used in these experiments, a large amplification of the Raman signal took place. Two other methods for obtaining polybithiophene–silver composite films are reported. In these cases, thanks to the silver particles, the polymer displays a SERS effect, which greatly improves the signal‐to‐noise ratio of the Raman spectra, thus allowing a much better vibrational analysis of both doped and undoped states.     

Understanding tip‐enhanced Raman spectra of biological molecules: a combined Raman,SERS and TERS study

Although conventional Raman, surface‐enhanced Raman (SERS) and tip‐enhanced Raman spectroscopy (TERS) have been known for a long time, a direct, thorough comparison of these three methods has never been carried out. In this paper, spectra that were obtained by conventional Raman, SERS (on gold and silver substrates) and TERS (in ‘gap mode’ with silver tips and gold substrates) are compared to learn from their differences and similarities. Because the investigation of biological samples by TERS has recently become a hot topic, this work focuses on biologically relevant substances. Starting from the TER spectra of bovine serum albumin as an example for a protein, the dipeptides Phe–Phe and Tyr–Tyr and the tripeptide Tyr–Tyr–Tyr were investigated. The major findings were as follows. (1) We show that the widely used assumption that spectral bands do not shift when comparing SER, TER and conventional Raman spectra (except due to binding to the metal surface in SERS or TERS) is valid. However, band intensity ratios can differ significantly between these three methods. (2) Marker bands can be assigned, which should allow one to identify and localize proteins in complex biological environments in future investigations. From our results, general guidelines for the interpretation of TER spectra are proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

白术煎剂表面增强拉曼光谱分析

测试分析了白术煎剂及其在银胶中的拉曼光谱,并对其进行初步谱峰归属。白术煎剂表面增强拉曼光谱在396,548,617,730,955和1 327 cm-1处,出现6个明显的拉曼信号。测试了白术煎剂和白术煎剂-银胶混合体系的紫外-可见吸收光谱,该吸收光谱在长波区出现新共振吸收峰(999 nm处),进而研究了白术煎剂在银溶胶上的吸附特性及其表面增强机理。结果表明,表面增强拉曼光谱可能为白术煎剂或其他中药煎剂提供一种准确、直接、快速的检测方法。     

碱性银胶的表面增强拉曼效应及对牛奶中三聚氰胺的检测

在合成银胶时加入适量的氢氧化钠,得到稳定性和均一性更好的碱性银胶,研究了它对不同浓度拉曼探针分子亚甲基蓝的增强效果。相比普通银胶,浓度的变化不对其和银胶的吸附方式产生影响,根本原因是碱性银胶对亚甲基蓝分子中硫原子的优向吸附而使451 cm-1处信号始终最强。研究了银胶对同浓度不同量的亚甲基蓝分子产生的拉曼增强效应,以及该拉曼增强光谱随时间的变化关系。另外,将该碱性银胶制备成银斑点应用于掺杂三聚氰胺的牛奶样品检测,获得了三聚氰胺掺入量和拉曼信号的线性关系,该方法需要样品量仅5 μL,拉曼光谱检测时间仅需5 s,非常适合快速测定分析,利用碱性银胶对三聚氰胺在691 cm-1处的特征拉曼峰,可在3～60 mg·L-1的范围内测定三聚氰胺的掺杂量,检出限达0.28 mg·L-1。     

Visible light response of silver 4‐aminobenzenethiolate and silver 4‐dimethylaminobenzenethiolate probed by Raman scattering spectroscopy

Silver thiolate is a layered compound with a Raman spectrum that is known to change with time, becoming the same as the surface‐enhanced Raman scattering (SERS) spectrum of the parent thiol molecule adsorbed on Ag nanoparticles. On this basis, the Raman scattering characteristics of silver 4‐aminobenzenethiolate (Ag‐4ABT) compounds were investigated to determine whether certain peaks that are identifiable in the SERS spectrum of 4‐aminobenzenethiol (4‐ABT) but absent in its normal Raman spectrum were also apparent in the Ag salt spectrum. For comparative purposes, the Raman scattering characteristics of silver 4‐dimethylaminobenzenethiolate (Ag‐4MABT) were also examined. Raman spectra acquired while spinning the sample were typified by only a₁‐type vibrational bands of Ag‐4ABT and Ag‐4MABT, whereas in the static condition, several non‐a₁‐type bands were identified. The spectral patterns acquired in the static condition were similar to the intrinsic SERS spectra of 4‐ABT or 4‐dimethylaminobenzenethiol (4‐MABT) adsorbed on pure Ag nanoparticles. Notably, the CH₃ group vibrational bands were observable for Ag‐4MABT irrespective of the sample rotation. In addition, no decrease in intensity during irradiation with a visible laser was observed for any of the bands, suggesting that no chemical conversion actually took place in either 4‐ABT or 4‐MABT. The preponderance of evidence led to the conclusion that the non‐a₁‐type bands observable in the SERS spectra must be associated with the chemical enhancement mechanism acting on the Ag nanoparticles. The chemical enhancement effect was more profound at 514.5 nm than at 632.8 nm, and was more favorable for 4‐ABT than 4‐MABT at both wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.     

SERS activity and stability of the most frequently used silver colloids

Single‐molecule detection by surface‐enhanced resonance Raman scattering (SERRS) spectroscopy has been demonstrated for a variety of molecules. The detection of single molecules that do not have a resonance contribution, SERS, has been shown in the case of adenine. However, when colloidal particles isolated on planar substrates are used as the enhancing medium, the presence of anomalous signals significantly complicates the analysis of the spectra. Selection of a silver colloid that minimizes these spurious signals should improve the ultra‐sensitive detection of non‐resonant single molecules by SERS. A range of silver colloids, prepared by different methods, were investigated with respect to their activity and stability. Minimal anomalous signals were obtained from hydroxylamine‐reduced silver colloids, which suggests that this colloid will be better for ultra‐sensitive SE(R)RS experiments compared to the more common citrate‐ and borohydride‐reduced silver colloids. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication and characterization of SERS‐active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4‐aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS‐based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80–100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 × 10⁴ relative to silver colloid, which might have resulted from the presence of ‘hot‐spots’ at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 × 10⁷ by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface. SERS‐based Raman mapping technique in the form of line scanning further illustrates the good SERS activity and reproducibility on the silver clusters. Finally, 4‐mercaptopyridine (4‐Mpy) was chosen as an analyte and the lowest detected concentration was investigated by the SERS‐active silver clusters. A concentration of 1.6 × 10⁻¹⁰ M 4‐Mpy could be detected with the SERS‐active silver clusters, showing the great potential of the technique in practical applications of microanalysis with high sensitivity. Copyright © 2006 John Wiley & Sons, Ltd.     

肿节风的表面增强拉曼光谱检测

提出一种基于表面增强拉曼光谱的中药材肿节风饮片的检测方法。采用柠檬酸三钠还原硝酸银制备银溶胶,以银胶纳米粒子为增强基底测得肿节风茎切片的表面增强拉曼光谱(SERS)。发现银胶直接作用于药材表面的SERS信号明显增强,肿节风茎切片SERS光谱中在637,1 176,1 309,1 476,1 612 cm^-1处都可观察到明显的拉曼特征峰。通过一阶导数拉曼光谱分析技术和对照品异嗪皮啶谱峰指认,可将获得的SERS峰位分别归属于吡喃酮环、甲氧基和酚羟基分子结构。研究结果表明,SERS技术可为肿节风和其他中草药的生产和质量监控提供一种快速、方便和直接的检测方法。     

Identification of berberine in ancient and historical textiles by surface‐enhanced Raman scattering

The highly fluorescent natural dye berberine can be easily identified in microscopic textile samples by surface‐enhanced Raman spectroscopy employing citrate‐reduced Ag colloid. The ordinary Raman (OR) and SERS spectra of berberine are presented and discussed in the light of a DFT calculation. Using FT‐Raman and FT‐SERS we could reliably compare relative intensity shifts and investigate the adsorption geometry of berberine on Ag nanoparticles. The significant enhancement in the FT‐SERS spectrum of the out‐of‐plane ring system bending deformation mode at 729 cm⁻¹ relative to a group of in‐plane vibrations at around 1500 cm⁻¹ was interpreted as evidence of a ‘flat‐on’ adsorption geometry. SERS was successfully used to identify berberine in silk fiber samples coated with colloidal Ag following a pretreatment with HCl vapor. The SERS method allowed us to detect berberine in a microscopic sample of a single silk fiber from a severely degraded and soiled 17th Century Chinese textile fragment. Copyright © 2007 John Wiley & Sons, Ltd.     

Fourier‐transform surface‐enhanced Raman spectroscopy (FT‐SERS) applied to the identification of natural dyes in textile fibers: an extractionless approach to the analysis

In the present study, an application of a silver colloid substrate in order to obtain Fourier‐transform surface‐enhanced Raman (FT‐SER) spectra of natural historical dyes is presented. In detail, we collected a spectral database from solutions of pure dyes and then we carried out extractionless both hydrolysis and non‐hydrolysis FT‐SERS analyses on wool fibers previously dyed in our laboratory and on ancient textiles. The term ‘extractionless’ refers to a method of SERS analysis applied directly on the fiber, thus avoiding the extraction of dyes from textile samples. The combination of a low‐energy source of radiation, as in the FT‐Raman technique, with SER spectroscopy can bring the important advantage of reducing the fluorescence typical of ancient samples and organic dyes. In some historical textile samples, for which SER spectra by use of visible excitation could not be obtained, the FT‐SER spectrum of an iron‐gall dye was recorded without hydrolysis, while, with an HF hydrolysis pre‐treatment on ancient fibers, madder, lac dye and brazilwood were clearly recognized. Copyright © 2014 John Wiley & Sons, Ltd.     

运用表面增强拉曼散射(SERS)和密度泛函数理论(DFT)模拟计算研究对硝基苯胺在金纳米颗粒表面吸附行为

在沉积金纳米颗粒的干燥滤纸上进行对硝基苯胺的表面增强拉曼散射(SERS)光谱研究,并与对硝基苯胺在金胶水溶液中的表面增强拉曼散射(SERS)光谱相比,分子拉曼光谱发生了很大变化。同时利用DFT理论计算对硝基苯胺在金胶颗粒上的吸附行为的拉曼光谱。DFT理论模拟计算和FI-Raman实验分析都表明这种变化源于对硝基苯胺的不同吸附方式。SERS和DFT结合研究分子的吸附是一种有效的技术。     

微波法制备银胶体及其在表面增强拉曼散射中的应用

本文提出了一种利用微波加热的原理,合成一种新型的银胶体溶液。该银胶具有高效的表面增强拉曼活性。以这种新型银胶体粒子作为活性衬底,测得的强荧光物质R6G的表面增强拉曼光谱,体现出荧光背景低,信噪比高的特点。通过两种不同方法制备的银胶体粒子的表面增强拉曼散射效果的比较,发现这种新型银胶纳米粒子通过聚集,形成更多的具有很强的提高样品表面增强拉曼散射强度作用的“热点”,从实验的角度验证了表面增强拉曼中的“热点”理论。     

Surface‐enhanced Raman spectroscopy for quantitative measurement of lactic acid at physiological concentration in human serum

Lactic acid is a simple and effective indicator for estimating physiological function. Rapid and sensitive detection of lactic acid is very useful in clinical diagnosis. However, the concentration of lactic acid in the physiological state is too low to be detected using traditional Raman spectroscopy. We applied silver colloidal nanoparticles‐mediated surface‐enhanced Raman spectroscopy (SERS) for rapid identification and quantification of lactic acid. The standard SERS spectra of lactic acid were defined and the 1395 cm⁻¹ band intensity was used for quantification from 0.3 to 2 mM (R² = 0.99). In clinical blood sample measurement, the ultrafiltration (cutoff value 5 kDa) can efficiently reduce background fluorescence to improve SERS performance. We established identical and optimal procedure by adjusting reaction time and volume ratio of serum and nanoparticles to obtain high SERS reproducibility. Finally, we showed that silver colloidal nanoparticles‐mediated SERS technique was successfully applied to detect lactic acid at physiological concentrations in the blood. Copyright © 2010 John Wiley & Sons, Ltd.     

Some aspects of SERS temporal fluctuations: analysis of the most intense spectra of hydrogenated amorphous carbon deposited on silver

Surface‐enhanced Raman scattering (SERS) spectra of hydrogenated amorphous carbon (a C:H) deposited on silver substrates have been recorded with a confocal Raman microscope. When scattered radiation is collected during a short time from an area of a few square micrometres, the subsequently measured SERS spectra often exhibit strong temporal changes (fluctuations). In this paper we present examples of spectra for which the intensity maxima of the fluctuating narrow Raman bands are significantly higher than that of the background (the background is usually dominated by two broad Raman bands centred at about 1350 and 1590 cm⁻¹). In a series of successively measured spectra, one can find spectra with noticeably different total integral intensity. This suggests that the results of averaging the spectra revealing strong and weak fluctuations may be different (at least in intensity). The influence of some electrolytes on the SERS spectral fluctuations is also analysed. Our experiments revealed that the efficiencies of quenching of the SERS spectral fluctuations by various electrolytes are significantly different. We suggest that only anions directly interacting with the metal surface quench strong SERS fluctuations, and that the large differences between chloride and perchloride solutions are caused by differences in the strength of interaction of Cl⁻ and ClO₄⁻ anions with the silver surface. Copyright © 2007 John Wiley & Sons, Ltd.